Part IV - Liability and Evidence

15 State Responsibility

Annalisa Savaresi *

15.1 Introduction

State responsibility is increasingly invoked in climate change litigation. It typically arises when an action or omission that is attributable to a State breaches an international obligation. However, as the International Court of Justice (ICJ) has noted, compliance with domestic law and compliance with international law are different questions.¹

International courts typically apply the general law of State responsibility as codified and elaborated by the International Law Commission.² Conversely, national courts tend to apply domestic rules when they consider arguments concerning a breach of an international obligation and pay limited attention to what the law of State responsibility says on these matters.³ The ICJ recognised this inconsistency when it stated that ‘what is a breach of treaty may be lawful in the municipal [domestic] law and what is unlawful in the municipal law may be wholly innocent of violation of a treaty provision’.⁴ As this chapter explains, however, the distinction between domestic and international law is sometimes blurred, especially in the dynamic field of climate change litigation.

Generally, domestic courts’ engagement with international law obligations is on the rise. This reflects a shift in the nature of international law itself, which has historically been concerned with ‘outward-looking’ State-to-State obligations to be implemented through conduct on the international plane. Now, the focus is increasingly turning towards ‘inward-looking’ obligations – whereby States are required to undertake certain conduct within their own jurisdiction, such as adopting a specific legal framework, according certain rights, or abstaining from taking particular actions.⁵ The latter type of international obligations are common in international environmental and human rights law. It is therefore not a surprise that international law obligations concerning environmental and human rights protection are, more and more, being invoked before national courts,⁶ especially in the context of climate change litigation.⁷ Domestic courts have thus inadvertently found themselves on the frontline of the enforcement of international obligations concerning climate change. There is, however, no uniform approach to the treatment of international obligations in general, and to the use of the law of State responsibility in particular, in domestic judicial practice.

This chapter expounds the fundamental tenets of the law of State responsibility, with a view to clarifying how this set of norms is used in the context of climate litigation. It starts with a succinct introduction to the law of State responsibility, illustrating its constituting elements and how they may apply to climate change. The chapter then considers how State responsibility has been framed in national judicial practice so far and what may be regarded as emerging best practice. This chapter does not consider legal redress that may be provided once responsibility for injury arising from a failure to fulfil that legal obligation has been established. The matter of damages is instead addressed in another chapter of this Handbook.⁸

15.2 The Law of State Responsibility

State responsibility typically arises when an action or omission that is attributable to a State breaches an international obligation,⁹ regardless of the origin or character of that obligation.¹⁰ As such, State responsibility requires neither fault nor damage.

Any ‘injured’ State, whose rights have been violated by said breach, may invoke State responsibility in an international dispute.¹¹ This may occur in a bilateral setting – for the breach of an obligation owed by one State to another – or in a multilateral setting – for the breach of an obligation due to multiple States, or indeed to all States.¹² The latter includes the possibility that the breach is ‘of such a character as radically to change the position of all the other States to which the obligation is owed with respect to the further performance of the obligation’.¹³ In both instances, an injured State must be specifically affected by the breach of an international obligation, for example because the wrongful act was committed against its citizens or on its territory.¹⁴ The remedies available under the law of State responsibility range from cessation of the wrongful act, to assurances of non-repetition, restitution, compensation, and satisfaction.¹⁵

In addition, any State may invoke State responsibility for the breach of obligations in the collective interest (so-called erga omnes or erga omnes partes obligations), even where it is not itself specifically affected.¹⁶ Thus, in the case of erga omnes obligations – such as, for example, the prohibition of genocide – the law of State responsibility may be invoked for wrongful acts committed against the citizens of another State and on the territory of another State.¹⁷ In these instances, however, the applicant State can only demand cessation of the internationally wrongful act and the performance of the duty to make reparation for the benefit of any injured States.¹⁸

In order to instigate a dispute for a breach of an international obligation concerning climate change, therefore, a set of conditions need to materialise:

1. 1. A State has international obligations that directly or indirectly concern climate change;

2. 2. One or more of these obligations have been breached, through an act or omission by the same State;

3. 3. The breach is attributable to said State;

4. 4. One or more States have been injured by said breach or the breached obligation is erga omnes/erga omnes partes.

The remainder of this section considers how the conditions to instigate an inter-State dispute for a breach of an international obligation concerning climate change may be fulfilled.

15.2.1 International Obligations Concerning Climate Change

As other chapters in this volume explain in further detail,¹⁹ there are several international law obligations concerning climate change. These obligations are primarily – though not exclusively – enshrined in international climate treaties, namely, the 1992 United Nations Framework Convention on Climate Change (UNFCCC), the 1997 Kyoto Protocol, and the 2015 Paris Agreement.²⁰ The numerous bodies created by these treaties have produced secondary rules that further articulate and substantiate parties’ obligations. While formally not legally binding, decisions of bodies like the Conference of the Parties (COP) to the UNFCCC provide authoritative guidance on the interpretation of climate treaties. States normally implement these decisions and regard them as part and parcel of the obligations under said treaties.²¹

Other international treaties, however, also provide obligations that are relevant to climate change.²² For example, the Multilateral Environmental Agreements (MEAs) on matters such as air quality, the protection of the ozone layer, biodiversity, and the conservation of the marine environment. Similarly, international law-making bodies other than those established under the climate treaties – like the International Civil Aviation Organisation and the International Maritime Organization – have produced international norms on specific climate related matters – such as, for example, emissions from aviation or maritime transport.²³

Similarly, climate change triggers States’ human rights obligations. It is by now widely recognised that climate change affects the enjoyment of virtually all human rights,²⁴ as well as that measures to respond to climate change can have significant human rights implications. The preamble of the Paris Agreement specifies that parties ‘should, when taking action to address climate change, respect, promote and consider their respective obligations on human rights’.²⁵ The UN Human Rights Council has adopted a series of resolutions emphasising the relevance of human rights obligations to climate change action, and the need to systemically interpret States’ obligations and corporate responsibilities in this connection, both at the national and international levels.²⁶

Finally, the body of customary international law includes obligations – such as those associated with the prohibition and prevention of transboundary harm²⁷ – which are explicitly mentioned amongst the general principles that should guide State parties to the UNFCCC as they set out to achieve the objective and implement the provisions of climate treaties.²⁸

15.2.2 Breach of an International Obligation

Establishing a breach of an international obligation requires careful examination of the content of the obligation and of the particular conditions required for it to be breached. This section provides a few examples, looking specifically at obligations enshrined in customary international law, in international climate change treaties, in other MEAs, and in human rights treaties.

15.2.2.1 Customary International Law Obligations

State obligations as established by customary international law may apply to climate change mitigation and adaptation. A State may, for instance, invoke a breach of the obligation to refrain from causing harm to the territory of another State and/or to areas beyond national jurisdiction. Under customary international law, an applicant State must prove that another State has caused transboundary harm or has breached the related obligation to prevent harm or the associated procedural duties to cooperate and to carry out an environmental impact assessment.²⁹ In relation to climate change, this requires demonstrating that the applicant State’s territory or an area beyond national jurisdiction has suffered significant harm (i.e. loss of life, loss of property, and/or environmental damage) as a result of activities producing greenhouse gas emissions carried out under the jurisdiction or control of the respondent State.

General international law, however, does not provide strict liability for transboundary harm arising from activities that fall within the exercise of a State’s sovereign rights.³⁰ An applicant State would therefore have to identify relevant due diligence obligations which have been breached by the respondent State. The fact that the respondent State has exercised reasonable diligence would be sufficient to exclude responsibility under international law, even if some significant harm has been suffered. Thus, an applicant State should provide proof that the respondent State has not put in place adequate procedures to assess and predict risks, to measure their probability and gravity, and to prevent and mitigate any harm.³¹ In international adjudication, therefore, ascertaining compliance with the obligation of due diligence to prevent, reduce, or control transboundary harm typically places a heavy burden of proof on prospective litigants to identify flaws in the discharge of due diligence obligations that are broadly worded and imprecise.³² States may, however, turn to the obligations enshrined in international environmental or human rights treaties, which substantiate what a State is expected to do in greater detail, as the next sections explain.

15.2.2.2 International Environmental Obligations

International climate treaties typically include obligations of conduct and obligations of result, which may be used to determine the contours of the general obligation to refrain from causing harm to the territory of another State and/or to areas beyond national jurisdiction. For example, Parties to the Paris Agreement must periodically prepare, communicate, and maintain plans – so-called ‘nationally determined contributions’ (NDCs) – detailing how they intend to reduce emissions and by how much, in order to contribute to holding the increase in the global average temperature to well below 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5°C.³³ NDC s are therefore a crucial resource to assess State parties’ conduct under the climate treaties. The Paris Agreement requires parties to periodically submit revised NDC s,³⁴ and failure to submit a revised NDC may be regarded as a breach of a State’s obligations of conduct under the Paris Agreement.

The substantive content of NDCs may be scrutinised in the context of parameters embedded in the Paris Agreement.³⁵ For example, the principle of ‘highest possible ambition’³⁶ may be interpreted as a due diligence standard that requires States to act proportionately in line with the risk at stake and the means at their disposal.³⁷ Scientists have repeatedly warned that the level of ambition embedded in NDC s submitted to date is insufficient to secure the achievement of the temperature goal envisioned in the Paris Agreement.³⁸ By and large, most extant NDCs do not adequately consider and mitigate the risk of harm to the territory of other States and to areas beyond national jurisdiction. NDCs that do not adequately contribute to the achievement of the temperature goal enshrined in the Paris Agreement may be regarded as a breach of a State’s obligations under that treaty.

Finally, international environmental obligations concerning the prevention of some specific forms of harm may also be invoked in the context of climate litigation. For example, the UN Convention on the Law of the Sea (UNCLOS) makes parties responsible for regulating and controlling the risk of marine pollution resulting from the activities of the private sector through an obligation of due diligence.³⁹ In fulfilling their obligations, UNCLOS parties are required to take into account ‘internationally agreed rules, standards and recommended practices and procedures’.⁴⁰ The due diligence obligations derived from UNCLOS may be read in light of obligations enshrined in climate treaties as well as decisions and guidance provided by their treaty bodies.⁴¹ Therefore, NDCs may be used as a yardstick to ascertain whether UNCLOS State parties are adequately considering and mitigating the risk of harm to the marine environment associated with climate change.

15.2.2.3 International Human Rights Obligations

Applicants in climate lawsuits increasingly invoke State responsibility for breaches of international obligations concerning the protection of human rights.⁴² This trend is part and parcel of a consolidated jurisprudential tradition, whereby a State’s human rights obligations are interpreted to encompass the duty to prevent and reduce environmental harm that interferes with the full enjoyment of human rights, providing for remedies for any remaining harm.⁴³ The obligation to protect human rights does not require States to prohibit all activities that may cause environmental harm. Instead, States have discretion to strike a balance between environmental protection and other legitimate societal interests. As both the first and the second Special Rapporteur on human rights and the environment have noted, however, this balance must not be ‘unjustifiable or unreasonable’ or result in unjustified, foreseeable infringements on human rights.⁴⁴

Over the years, judicial and quasi-judicial international human rights bodies have developed a rich practice providing remedies affording relief to victims of human rights abuses, drawing on the law of State responsibility and domestic jurisprudence.⁴⁵ Even if human rights treaties are not designed to protect the environment as such – and only some expressly guarantee a right to a safe, clean, healthy, and sustainable environment – human rights bodies have increasingly awarded indirect protection to environmental interests, insofar as they are linked to the enjoyment of human rights.⁴⁶ The unique supernational remedies provided by international human rights instruments have been increasingly used also as a means to bridge the compliance and accountability gaps that characterise environmental governance. And even when they do not have the power to award remedies, these bodies exert influence over domestic judicial practice interpreting the scope and content of human rights obligations.⁴⁷ As Section 15.3 of this chapter shows, in recent years, this practice has become apparent with regard to climate change.⁴⁸

Human rights bodies generally recommend that States strike an appropriate balance between evidential burdens of proof between the claimant and the defendant, whereby account is taken of the differences in power and capacity of the parties.⁴⁹ According to the Committee on Economic, Social and Cultural Rights, for example, ‘shifting the burden of proof may be justified where the facts and events relevant for resolving a claim lie wholly or in part within the exclusive knowledge of the corporate defendant’.⁵⁰ As Section 15.3 of this chapter shows in greater detail, this interpretation of the evidential burden of proof is yet another reason why climate applicants increasingly resort to human rights arguments.

15.2.3 The Breach is Attributable to a State

The law on State responsibility includes rules of attribution of conduct of persons or entities to a State.⁵¹ In the case of a plurality of responsible States, the general rule is that each State is separately responsible for conduct attributable to it.⁵²

Attributing breaches of obligations enshrined in climate treaties can be relatively straightforward. For example, submitting NDCs is a formalised process that clearly entails State agency. Therefore, if a State omits to submit an NDC, or submits a wholly inadequate NDC, these actions and omissions can be attributed to said State. It seems in other words unlikely that, in instances such as these, State agency may come under dispute.

Climate lawsuits frequently allege human rights violations associated with the emissions produced on the territory of the respondent States, or as a result of activities carried out on the State’s territory, which in turn are predicted to have an effect on global climate.⁵³ In both cases, the State’s responsibility arises from failure to regulate a hazardous activity within its jurisdiction or control.

While traditional interpretations of human rights treaties have often equated the scope of a State party’s jurisdiction with the State’s territory,⁵⁴ human rights bodies have progressively recognised the extraterritorial reach of a State’s human rights obligations.⁵⁵ In a groundbreaking Advisory Opinion, the Inter-American Court of Human Rights (IACtHR) has suggested that States have the obligation to prevent any significant environmental harm inside or outside their territory, produced by themselves or third parties within their jurisdiction.⁵⁶ According to the Court, when transboundary harm or damage occurs, a person is under the jurisdiction of the State from which the harm originated if there is a causal link between a conduct that occurred within the territory of that State and the negative impact on the human rights of persons outside the territory of that State.⁵⁷

15.2.4 Injured State/Erga Omnes Obligations

Under international law, a State needs to be specifically affected by a breach of an international obligation to invoke the law of State responsibility, most commonly because the wrongful act was committed against its citizens or on its territory.⁵⁸ States that are particularly vulnerable to the adverse effects of climate change are already singled out in the climate treaties as deserving special attention and support and benefit from special treatment.⁵⁹ These States could therefore claim to be injured by breaches of international obligations due to human rights violations suffered by their citizens as a result of climate change.

Alternatively, any State may invoke the responsibility of another State for a breach of erga omnes partes obligations. For example, some human rights obligations – like the prohibition of torture – are erga omnes.⁶⁰ Furthermore, some obligations arising from the Paris Agreement – such as, for example, that to submit an NDC – may be regarded as erga omnes partes.⁶¹

15.3 State of Affairs

15.3.1 International Practice

While the possibility to instigate an international dispute alleging State responsibility for a breach of an international obligation concerning climate change has been at the centre of much scholarly speculation, no such litigation has materialised so far. At the time of writing, however, three parallel initiatives concerning the request of an advisory opinion on climate change from international courts are underway.⁶² Advisory opinions ‘constitute advice’ and ‘do not legally bind either the requesting entity or any other body or State to take any specific action pursuant to the opinion’.⁶³ Even so, advisory opinions might provide crucial guidance to better define the contours of States’ obligation of due diligence to prevent, reduce, or control transboundary harm associated with climate change.

In the first initiative, the Pacific Island State of Vanuatu has launched a campaign to seek an advisory opinion from the ICJ, with a view ‘to clarify[ing] the legal obligations of all countries to prevent and redress the adverse effects of climate change’.⁶⁴ The proposed questions are:

1. (1) What are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases for present and future generations?;

2. (2) What are the legal consequences under these obligations for States which, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:

   1. (a) States, including, in particular, small island developing States, which, due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change?

   2. (b) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?⁶⁵

In March 2023, the proponents secured support for a formal request for an advisory opinion by the UN General Assembly, as required by the UN Charter.⁶⁶

In the second initiative, the Commission of Small Island States on Climate Change and International Law⁶⁷ has sought an advisory opinion from the International Tribunal on the Law of the Sea.⁶⁸ As noted earlier, while the UNCLOS does not deal with greenhouse gases specifically, these gases may be regarded as pollutants, falling within the scope of parties’ due diligence obligations to regulate and control the risk of marine pollution.⁶⁹ The questions before the court are:

What are the specific obligations of State Parties to the United Nations Convention on the Law of the Sea (the ‘UNCLOS’),

1. (a) to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas emissions into the atmosphere?

2. (b) to protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?⁷⁰

The tribunal has invited selected international organisations and stakeholders to present written statements and held hearings in September 2023.⁷¹

Finally, in January 2023, Chile and Colombia asked the IACtHR for an advisory opinion on climate change and human rights, with a view to support a fair, sustainable, and timely response to the climate emergency, taking into account the obligations arising from international human rights law.

The guidance delivered as a result of these requests for an advisory opinion would be particularly helpful in the context of climate litigation before domestic and regional courts, where arguments concerning the breach of international obligations are increasingly made.

In the meantime, some human rights-based complaints related to climate change have already been brought before international quasi-judicial (namely, the UN Human Rights Committee,⁷² the Committee on the Rights of the Child⁷³) and non-judicial human rights bodies (namely, various Special Procedures of the Human Rights Council).⁷⁴ The vast majority of these complaints remain pending or have failed to reach adjudication on the merits due to admissibility constraints.⁷⁵ Three important decisions have already been issued.

In Teitiota, one asylum seeker lodged a complaint with the UN Human Rights Committee against New Zealand. He alleged that New Zealand’s refusal to grant him asylum threatened the enjoyment of his right to life, as a result of risks associated with climate change-induced displacement. The Committee found that the applicant’s complaint did not concern ‘a hypothetical future harm, but a real predicament’ and that ‘the risk of a violation of the right to life had been sufficiently substantiated’.⁷⁶ It nevertheless rejected the complaint at the merits stage,⁷⁷ as it was not satisfied that the applicant would have been personally affected by a serious individualised risk should he be sent back to Kiribati.⁷⁸ The Committee reasoned that only in ‘extreme cases’ can it find a violation of the non-refoulement obligation stemming from the right to life based on a situation of ‘a serious and generalized risk’ in the country of origin. According to the Committee, the general situation in Kiribati did not qualify as an extreme case, as the country could, with the assistance of the international community, ‘take affirmative measures to protect and, where necessary, relocate its population’.⁷⁹ Even though the complaint was unsuccessful, the UN Human Rights Committee’s reasoning concerning State obligations vis-à-vis threats to life associated with climate change is important to determine the scope of a State’s obligations under human rights law. The Committee acknowledged that climate change constitutes ‘one of the most pressing and serious threats to the ability of present and future generations to enjoy the right to life’⁸⁰ and that the effects of climate change may expose individuals to a violation of their rights under the Covenant, ‘thereby triggering the non-refoulement obligations of sending States’.⁸¹ The Committee’s reasoning has already made strides in domestic judicial practice. In 2021, the Italian Court of Cassation cited the Committee’s decision in Teitiota, asserting that national judges should consider environmental or climate degradation that may put at risk personal dignity of asylum seekers in the country of origin.⁸²

In Sacchi et al, a group of children from multiple countries filed a complaint before the Committee on the Rights of the Child against multiple States. They lamented that the defendant States had breached their rights to life, health, culture, and best interest of the child, as a result of failure to adopt adequate measures for climate change mitigation.⁸³ Although their complaint was dismissed at the admissibility stage due to lack of exhaustion of domestic remedies, the Committee’s reasoning concerning the scope of the respondent States’ jurisdiction is particularly important. The respondent States had argued that the applicants were not within their jurisdiction. The Committee rejected this argument, applying the IACtHR’s reasoning mentioned earlier. It noted that emissions originating in the respondent States contribute to climate change and that the adverse effects thereof have implications on the enjoyment of human rights by individuals ‘both within as well as beyond the territory of the State party’.⁸⁴ The Committee noted that, due to their ability to adopt and enforce regulations on emitting activities, the respondent States had ‘effective control’ over the source of the harm.⁸⁵ The Committee established that, under the principle of common but differentiated responsibilities and respective capabilities, every State is responsible for its own share of greenhouse gas emissions, as the collective nature of the problem does not absolve individual States of their responsibility for ‘the harm that the emissions originating within its territory may cause to children, whatever their location’.⁸⁶ The Committee noted that the transboundary harm at the centre of the applicants’ complaint was foreseeable, due to the scientific evidence on climate change impacts and the fact that the respondent States had signed international treaties on climate change.⁸⁷

Finally, in Daniel Billy, Australian indigenous peoples alleged violations of the right to culture, right to privacy, family, and home, and right to life, as a result of Australia’s failure to take adequate measures to mitigate and adapt to climate change. The UN Human Rights Committee granted their complaint only with regard to Australia’s lack of timely and adequate action over climate change adaptation. The Committee found that the applicants had provided sufficient information on how they had personally been affected by the impacts of climate change.⁸⁸ It asserted that Australia had failed to comply with its positive obligation to protect the applicants’ home, their private and family life, and their collective ability to maintain a traditional way of life and to transmit their customs and culture to future generations.⁸⁹ As in Teitiota, however, the Committee did not find a violation of the right to life, as the applicants had not demonstrated a concrete and reasonably foreseeable risk that their life would be exposed to, or the effects that climate change had already had on their health. Instead, the Committee emphasised that, in the period of time in which the islands would allegedly become uninhabitable, Australia could undertake preventive measures and, if necessary, relocate the applicants.⁹⁰

15.3.2 Regional Practice

Regional human rights bodies, too, have been increasingly asked to consider complaints concerning climate change.⁹¹ At the time of writing, fourteen climate complaints have been filed before regional human rights bodies⁹² – ten with the European Court of Human Rights (ECtHR),⁹³ three with the and the Inter-American Commission on Human Rights,⁹⁴ and one with the European Committee of Social Rights.⁹⁵

These applications build on the consolidated case law of the ECtHR and IACtHR on environmental matters and typically rely on the human rights that these courts have over the years identified as relevant to the protection of environmental interests – such as the right to life, the right to respect for private and family life, home and correspondence, the rights of indigenous peoples – especially, those to culture and to communal property – and procedural rights associated with access to participation, information, justice, and remedies.⁹⁶

In the only complaint that has been adjudicated on the merits to date – Marangopoulos Foundation for Human Rights (MFHR) against Greece – the applicants lamented breaches of their right to health, as a result of the operation of lignite mining. The case therefore addressed climate change concerns only indirectly. The European Committee of Social Rights declared that Greece had not applied legislation satisfactorily and had not provided sufficiently precise information and screening of the health hazards related to lignite mining. The Committee cited the International Law Commission Articles on the Responsibility of States for Internationally Wrongful Acts,⁹⁷ which provide that, when a State is under an international obligation to take preventive action against a certain event, but fails to do so, the State remains in breach over the entire period during which the event continues. Consequently, the Committee considered that the issues raised in the complaint constituted a breach of the obligation to prevent damage arising from air pollution for as long as the pollution continued, and that the breach might even be compounded progressively, if no sufficient measures were taken to put an end to it.⁹⁸

15.3.3 Domestic Case Law

As noted earlier, international law obligations have become a common yardstick that domestic courts use to ascertain the lawfulness and adequacy of national law measures to tackle climate change and their impacts, and lack thereof. There is by now a rather long series of climate cases in which national courts rely on a combination of national and international law to order State authorities to take more ambitious action on climate change mitigation or adaptation.⁹⁹ These judgments variably rely on a blend of tort, public, or human rights law obligations, interpreted and reviewed in light of international law obligations.¹⁰⁰ Admittedly, this is a rather artificial distinction, given that in most cases the courts rely on multiple legal grounds to justify their findings. Nevertheless, some commonalities between successful climate cases concerning State responsibility do exist. These judgments recognise that State responsibility can be established for failure to adopt laws and policies that adequately deal with the climate emergency. Compliance with international law obligations is used as a yardstick to assess the adequacy of domestic climate law measures. Here we provide some examples of judgments from all over the world, combining international and domestic law arguments, which have delivered decisions favourable to climate applicants.

In Ashgar Leghari v Federation of Pakistan et al, Pakistani courts ordered the creation of a Climate Change Commission, tasked to monitor the implementation of the National Climate Change Policy, as a means to address the grievance of a farmer, who had lamented that lack of enforcement of existing national policies on climate change adaptation had breached his human rights.¹⁰¹ The court relied on Pakistan’s international environmental obligations, read in conjunction with established case law deriving the right to a healthy environment from extant constitutional rights.¹⁰²

In Salamanca Mancera v Presidencia de la República de Colombia,¹⁰³ Colombian courts ordered the government to stop deforestation in the Amazon, finding that the State had breached the human rights of the young applicants, as well as its obligations under international climate treaties.¹⁰⁴

In Commune de Grande-Synthe v France,¹⁰⁵ the French Council of State found that the French government’s failure to reduce greenhouse gas emissions violated its duty of care. The court relied on the French Civil Code’s provisions concerning tortious liability for environmental damage and construed the State’s duty on the basis of international obligations enshrined in the European Convention of Human Rights and in the Paris Agreement.

In Neubauer and others v Germany, the German Constitutional Court formulated the State’s duty to align climate laws with the best available climate science,¹⁰⁶ in light of international law obligations enshrined in the Paris Agreement.¹⁰⁷ According to the Court, the duty to protect arising from constitutional rights and the obligation to take climate action ‘possesses a special international dimension’.¹⁰⁸ The Court specifically pointed to the necessity to implement a State’s own climate measures at the national level and not to create incentives for other States to undermine international cooperation.

In re Greenpeace Southeast Asia and Others, the Commission on Human Rights of the Philippines carried out an inquiry on the impact of climate change on the human rights of the Filipino people, and on the role of the so-called Carbon Majors in this regard. The Commission asserted that States’ obligations to respect, protect, and fulfil human rights require them to adopt and implement measures to prevent human rights violations, including those carried out by non-State actors.¹⁰⁹ The Commission relied on the IACtHR’s Advisory Opinion to affirm that States have the responsibility to ensure that activities under their jurisdiction do not interfere with the enjoyment of human rights of people outside their jurisdiction.¹¹⁰ It further noted that, for the purposes of finding that a State is in violation of its human right obligations in the context of climate change, ‘it is sufficient to establish the absence of meaningful State resolve and action to address the major anthropogenic actors and factors driving global warming’.¹¹¹

The Dutch courts have, however, made the most consequential statements regarding State responsibility for climate change, in the judgments in Urgenda Foundation v the State of the Netherlands.¹¹² While Urgenda is examined in greater detail elsewhere in this Handbook,¹¹³ for the purposes of the present chapter, these judgments delivered the following key findings. First, international law obligations are relevant to determine the contours of the State’s responsibility for climate change under domestic law; and second, domestic courts may order State authorities to address a breach of an international obligation.

The Dutch courts defined the contours of the State’s responsibility under domestic law, in light of obligations enshrined in international law. Under the Dutch Constitution, provisions of international law that are ‘binding on all persons’ are directly applicable in national courts.¹¹⁴ In Urgenda, the Dutch Supreme Court found that, because there is a grave risk that dangerous climate change would endanger the lives and welfare of many people in the Netherlands, the State had a responsibility ‘to take adequate measures to reduce greenhouse gas emissions from Dutch territory’.¹¹⁵ This duty to take the ‘necessary measures’ to mitigate climate change, in accordance with the State’s specific responsibilities and capabilities, was construed on the basis of rights enshrined both in the European Convention on Human Rights – a treaty commonly regarded as having direct effect in the Netherlands – and in the UNFCCC and the Paris Agreement – which do not have direct effect.¹¹⁶ The Court also relied on the no harm principle enshrined in customary international law to find that the Dutch State must take action to prevent harm to other countries arising from climate change, even if they are only partially responsible.¹¹⁷ The Supreme Court explicitly referenced rules from the International Law Commission’s Draft Articles on State Responsibility concerning situations where there are multiple States involved in a breach of an international obligation.¹¹⁸ Since Urgenda did not claim damages and instead only asked the courts for an order to perform an obligation, the Supreme Court did not explore how multiple States should share reparation or compensation in relation to climate change. Still, the Court emphasised that the fact that other States fail to meet their responsibility is no ground for the State not to perform its obligations.¹¹⁹

The Supreme Court also found that the fact that Dutch emissions are relatively modest is no ground for non-performance. Otherwise, a State could simply avoid responsibility by pointing to the responsibility of other nations for emissions.¹²⁰ The Court suggested that no single reduction is negligible, since every reduction has a positive effect in diminishing dangerous climate change.¹²¹ As noted in other chapters of this Handbook,¹²² the Dutch judges specifically rejected the ‘drop in the ocean’ defence put forward by the government, noting that ‘Urgenda does not have the option to summon all eligible States to appear in a Dutch court’.¹²³ The Court of Appeal established that causality ‘only plays a limited role’ when the matter of the dispute is not the award of damages.¹²⁴ Instead, the Court reasoned, when damages are not at stake, ‘a real risk’ of a danger for which measures must be taken is sufficient for a complaint to be admissible.¹²⁵

15.4 Best Practice and Replicability

This chapter has considered the extent to which climate judgments rely on State responsibility. It illustrated the core elements of this notion in international law and analysed extant international, regional, and national practice. It has shown that domestic courts have established State responsibility on several occasions, relying on multiple legal grounds to justify their findings, including by reading tort, human rights, or constitutional law in light of international law. There are commonalities between successful climate cases invoking State responsibility. The applicants typically argue that the State’s climate laws or policies concerning mitigation are either not ambitious enough or not adequately implemented. Judicial and non-judicial bodies alike have rejected the ‘drop in the ocean’ arguments and recognised that State responsibility can be established, for failure to adopt laws and policies that adequately deal with climate change. Not only are these decisions replicable, but, as more and more States adopt climate legislation, litigation demanding greater alignment between international law obligations and national legislation is likely to become more common.

The Urgenda judgments are illustrative of how national courts may rely on the law of State responsibility, and specifically, on breaches of international law – including the European Convention on Human Rights, the UNFCCC, and the Paris Agreement – to order a State to take (better) measures to tackle climate change. Admittedly, making this kind of argumentation is easier in ‘monist’ States, like the Netherlands, where international law obligations are directly applicable in domestic law.¹²⁶ For example, in another monist State, Belgium, domestic courts adjudicated a case that was filed on grounds that were broadly similar to those put forward in the Urgenda lawsuits, with similar judicial outcomes.¹²⁷ However, as this chapter has already shown, national courts in dualist States have also been willing to accept arguments on State responsibility similar to those made in the Urgenda judgments.¹²⁸

At the time of writing, Daniel Billy remains the only decision of an international human rights body granting the claims of climate applicants. The decision was construed on the basis of the rights to culture and home, private and family life, and recognised human rights violations resulting from the State’s failure to undertake measures to ensure climate change adaptation. The decision has affirmed that States must take adaptation measures to comply with their human rights obligations.¹²⁹ The decision, however, has left unaddressed questions over States’ human rights obligations concerning mitigation, neither confirming nor disproving the interpretation of these obligations provided in the Urgenda judgements.¹³⁰

The judgments and decisions reviewed in this chapter have broken new ground and will continue to inform and influence future judicial practice interpreting the scope and contours of State responsibility. At least with reference to climate change, questions of compliance with domestic and international law may not be very different, after all.

16 Causation

Lisa Benjamin and Sara Seck ^*

16.1 Introduction

This chapter covers the legal test of causation and how it has appeared and been adjudicated in climate litigation. The causation test arises in climate litigation most often, but not always, in the guise of a tort-based standard which appears to pervade the approaches of many legal systems to managing climate harms. The definition of causation varies from jurisdiction to jurisdiction but will often involve some required proximity between the actions of the defendant and the harm caused to the plaintiff. Due to the nature of climate change, this proximity has in the past been difficult for plaintiffs to prove. However, as this chapter illustrates, issues of causation can also arise in other areas of law, including legal tests for standing and assessment of remedies for future harms.

The causation test has proven to be one of the major hurdles in some forms of climate litigation. This is particularly so for tort-based climate litigation, where plaintiffs must prove that the defendant’s actions caused the plaintiff harm. The traditional approach of tort law in common law countries follows the general ‘but for’ test: but for the defendant’s actions, the plaintiff would not have suffered harm. For example, in the United States (US), tortious conduct must be a factual cause of harm for liability to be imposed. Conduct is a factual cause of harm when the harm would not have occurred absent the conduct.¹ While the test varies between jurisdictions, in most jurisdictions the cause must precede the harm. The legal test for causation usually relies on a preponderance of the evidence or, in some common law jurisdictions, a 50 per cent or more probability that the breach of the duty caused the harm. In civil law jurisdictions, the test of ‘conditio sine qua non’ (or ‘without which it could not be’) does not have a similar numerical threshold but does require that the court is convinced that a causal link exists.²

There are both general and specific elements of causation. General causation relies on the establishment of a cause-and-effect relationship between the act and the harm. In other words, whether the alleged causal factor can cause the type of effect from which the plaintiff suffers. Specific causation focuses on the specific harms alleged by the plaintiffs. In other words, whether the alleged causal factors did indeed cause the particular injury alleged by the plaintiff.³ Specific causation involves a larger variety of factors, including the levels, duration, and proximity of exposure.⁴

16.1.1 Causation in the Climate Context

In the climate context, causation analysis involves highly complex and multi-tiered scientific inquiries about human influence on the climate.⁵ Scientific studies usually adopt probabilistic inquiries, which may at first glance be unrecognisable from the traditional legal understanding of tortious causation. On a closer examination, however, there are synergies between climate and legal causation – both involve an assessment of probabilities.

In the climate context, the causal chain is often more extended than in other fields of litigation. Greenhouse gases (GHGs) are mixed in the atmosphere, and it is therefore difficult if not impossible to identify the emissions of one source of GHGs from another. Climate harms result from cumulative and aggregate emissions and the reduction of carbon sinks, making climate change essentially a stock problem. Climate impacts experienced now can be a result of historical emissions; therefore, time is also a factor. Emissions produced decades ago may only now be causing concrete impacts and harms. In addition, emissions made today are likely to contribute to future harms due to the existing stock of historical emissions. The duration between emissions, and the harm those emissions caused, can be problematic in proving specific causation. In addition, it is difficult to identify a specific defendant whose emissions caused specific harm to a specific plaintiff.

Advances in both attribution science and climate science generally are closing these causal gaps. The 2021 Intergovernmental Panel on Climate Change (IPCC) report identified that each 1,000 GtCO₂ of cumulative emissions is likely to cause a 0.27°C to 0.63°C increase in global surface temperature with a best estimate of 0.45°C.⁶ This is called the ‘transient climate response to cumulative CO₂ emissions’.⁷ In other words, every tonne of CO₂ adds to the global warming effect; every emission counts. This finding can bolster broader approaches to causation in climate impact cases.

There are four main elements in the climate-related causal chain.⁸ The first is the establishment of the relationship between cumulative GHG emissions in the atmosphere to increases in global mean temperatures. The second is the establishment of the relationship between temperature increases and harmful effects. The third is the attribution of a specific weather event (usually an extreme event) to general warming trends (this is sometimes called ‘impact attribution’ or ‘event attribution’). An additional fourth element is source attribution (attribution of an actor’s or project’s contributions to global cumulative GHG emissions). Courts sometimes take different approaches to causation on this element, between liability for States as opposed to corporations.

The complex causal relationships described earlier are not always easily accommodated by the law. In Section 16.2, we will discuss how courts have grappled with these complexities. This section also provides background context to the theories of causation in tort law, the connection between causation and standing, and the nexus between causation and human rights claims and attribution science.

Section 16.3 provides an analysis of the state of affairs in climate litigation around causation in different types of cases. The first part of this section focuses on cases requesting redress for past climate harm or past actions (such as the issuance of a permit). As will be seen, some of these cases do not seek remedy for specific climate harms but rather seek to prevent ongoing and future GHG emissions. This focus on prevention is also prevalent in the policy cases discussed in the second part of Section 16.3, all of which request a cessation or reduction of emissions in order to prevent or mitigate future climate harm.

Section 16.4 then sets out what we consider to be emerging best practices in judicial approaches to causation in the climate context. Finally, Section 16.5 considers the replicability of these best practices in other jurisdictions.

16.2 Background Context

16.2.1 Causation in Tort Law

Tort law is designed to remedy human-based harms. Therefore, taking a broader conceptual approach to the role of tort law and its remedial purpose can make it a more malleable and therefore useful legal concept in climate litigation. There are existing examples of where tort law has adapted in order to provide a fair remedy in complex circumstances. This approach to tort law, and specifically causation in tort law, can also contribute to emerging best practice in climate litigation – discussed in Section 16.4.

Examples of conceptual evolution in tort law related to causation include the recognition of collective harm,⁹ where independent tortious actions of multiple defendants produce a single harm, but it is impossible to determine which actions of one or more defendants caused the harm. Another is the market share liability theory, where several defendants produce harmful products but only one caused the harm to a particular plaintiff. Under this theory, if a plaintiff cannot identify one defendant, she can claim against every manufacturer of the harmful products in proportion to its share of the market.¹⁰ Another is the commingling product theory,¹¹ where multiple independent actors combine and the result of their cumulative products is to produce a single, indivisible harm.

Many of these theories have been developed over time by courts to apply in narrow circumstances, usually where the products are fungible and the plaintiff (through no fault of her own) is unable to identify one or all of the defendants responsible for the harm. Similarly, plaintiffs in climate cases are unable to identify one responsible emitter, due to the nature of GHGs (see Section 16.1.1). Courts could, and some have, expanded or adapted existing theories to accommodate the complex causal relationships involved in climate change. Failure to do so is likely to leave many plaintiffs without remedy. This flexibility is illustrative of emerging best practice and has been adopted in some cases highlighted later.

16.2.2 Causation, Standing, and the Nature of Plaintiffs and Defendants

Causation arguments arise in other areas of climate litigation beyond torts, such as in relation to the procedural hurdle of standing. It is often necessary to prove some element of causation for the purpose of establishing standing in order to proceed to the merits of the claim. The specific parties granted standing by the court will also impact the nature of the causative inquiry undertaken by the court.

In US federal courts, for example, there are three elements to establish standing: injury, traceability, and redressability. The plaintiff must have suffered an injury in fact, which is fairly traceable to the challenged conduct of the defendant (a causation-type element) and which is likely to be redressed by a favourable judicial decision.¹² An injury in fact must be an injury that is an invasion of a legally protected interest, which is particularised, concrete, and actual or imminent.¹³ The injury must be specific to the litigant and not theoretical.

However, cases have confirmed that the injury to be proved for standing does not have to be capable of sustaining a cause of action under tort law, and so the application of causation is separate and apart in a standing analysis. Therefore, a wider variety of injuries is usually accepted by US courts in order to establish standing than might be accepted under tort law, such as aesthetic, emotional, or psychological injuries. An example from the climate litigation world is the Massachusetts v EPA case,¹⁴ where the Supreme Court held that Massachusetts had ‘special solicitude’ as a state, and a sovereign interest in the Environmental Protection Agency (EPA) exercising its authority under the Clean Air Act to regulate GHG emissions.

In another example, in Funk v Wolf,¹⁵ a court in Pennsylvania found that the youth plaintiff did have a substantial, direct, and immediate interest. Funk was a 10-year-old who sued the Pennsylvania governor and public utility for failing to develop a comprehensive plan to regulate CO₂ emissions. Funk’s interest was found to be direct if there is a causal connection between the matter complained of and the harm alleged. The court found that the interest is immediate if the causal connection is not remote or speculative. In this case, Funk’s asthma prevented him from going outside and the right to enjoy public natural resources was harmed by ongoing environmental degradation (although the court found that the relief requested by the plaintiff was not redressable).

It can be difficult for an individual plaintiff to establish that they suffered a particularised injury to herself or to her property in the context of climate change that merits remedy. This is a particularly ‘live’ issue in the human rights context, and especially so for foreign plaintiffs. In the German Neubauer case,¹⁶ the Constitutional Court granted standing to German youth complainants as well as complainants living in Nepal and Bangladesh as natural persons claiming duties of protection and violation of their fundamental rights.¹⁷ The Court found that the plaintiffs had established an individual interest to challenge the German government’s insufficient climate mitigation targets, despite the fact that many people would be similarly affected by the government’s restrictions in the future. The claimants argued that the GHG emissions reduction goals in the Federal Climate Protection Act were insufficient in light of the State’s obligations under the Paris Agreement and Germany’s constitutional human rights law. The Court observed that climate change ‘is a genuinely global phenomenon and could obviously not be stopped by the German State on its own. However, this does not render it impossible or superfluous for Germany to make its own contribution toward climate change’.¹⁸ Nevertheless, the Court ultimately rejected the claims of the complainants from Bangladesh and Nepal, citing in part the limits of German sovereignty under international law which would limit the State’s ability to implement adaptation measures.¹⁹ On the other hand, the German youth complainants were successful.

Despite these examples, hurdles relating to causation have contributed to other cases failing on the basis of standing. The early case of Kivalina v ExxonMobil²⁰ is an example of an attenuated causal chain leading to a court finding no standing on behalf of the plaintiffs. Juliana v United States²¹ is a newer iteration of the standing problem, with the court finding a lack of redressability by the judiciary and therefore a lack of standing.

Given that causation requires proof that the defendant’s conduct caused or is causing the plaintiff’s harm or future harms, the success of climate litigation in which causation is an issue may be dependent upon which plaintiffs are allowed to proceed, and consideration of causation may seep into this analysis even if not made explicit. Plaintiffs in climate actions in which causation is an issue may find their standing challenged on the basis of whether or not they are individuals or groups, including non-governmental organisations (NGOs) seeking public interest standing, and whether or not actions can be brought on behalf of future generations.

The case law is not consistent on these questions, but the result of this initial stage in proceedings has implications for what must be established in the causation analysis. For example, a common challenge in the certification of climate-related class actions is the need for a court to ensure that members of the class raise common issues that can be resolved efficiently and effectively through the class action procedure.²² In Milieudefensie et al v Royal Dutch Shell,²³ class certification led to the bundling of the claims brought by Dutch-based NGOs to the extent that they serve the interests of Dutch residents and inhabitants of the Wadden region, including future generations. However, the court held that the interests of the world’s population, both current and future generations, were not acceptable for bundling as part of these collective claims even as argued by the same Dutch-based NGOs.²⁴ The subsequent analysis, including with respect to causation, repeatedly refers back to the implications of climate change for inhabitants of the Netherlands and the Wadden region.²⁵

The nature of the defendant is also important for the causation analysis, as evident when litigation against States is compared to litigation against non-State actors, especially business enterprises. For example, claims against States may raise concerns with regard to overarching climate policy,²⁶ or alternately permit approvals issued by government decision-makers and agencies may be appealed or judicially reviewed by a court.²⁷ An agency’s consideration of a permit approval could be insufficiently narrow if it failed to take a hard look at the severity of the impacts of GHGs which would result from its approval. These could include global emissions, as well as national impacts, with courts sometimes, but not always, looking closely at the nature of the impacts on the plaintiffs themselves.²⁸ These issues have arisen in relation to agency approvals of fossil fuel-related activities in many different jurisdictions and are often intertwined with other considerations, including local social and environmental impacts as well as Indigenous rights. Alternatively, claims may be brought directly against fossil fuel enterprises and others, whether seeking remedy for harm arising from emissions, or raising concerns over the global and local impacts of the enterprise’s climate policy.²⁹

16.2.3 Causation and Human Rights

The nature of the causation analysis differs when human rights are invoked. This has been explicitly noted in the non-climate context with regard to the approach of the European Court of Human Rights (ECtHR).³⁰ Turton observes that while negligence actions in the United Kingdom (UK) require that the defendant’s conduct was either a ‘but-for cause of, or materially contributed to’ the damage suffered by the plaintiff, it is enough in a human rights claim to establish that the defendant’s conduct violated ‘the relevant right’.³¹ This reflects the approach adopted in the South Africa Groundwork Trust climate case concerning public law remedies and threats to constitutional rights: ‘In terms of section 38 of the Constitution, litigants are entitled to approach a court for relief where rights are infringed or threatened’. There can be no doubt that unsafe levels of ambient air pollution directly threaten constitutional rights.³²

The nature of human-induced climate change makes it challenging to assert that there is a direct link between GHG emissions by a particular defendant State (or company) and violations of any particular human right. However, this hurdle is not insurmountable. For example, the Dutch Supreme Court in Urgenda³³ applied the precautionary principle and drew upon ECtHR jurisprudence³⁴ to clarify that proof of causation is not required in human rights cases raising environmental hazards – including climate change – as State obligations under Articles 2 and 8 of the European Convention on Human Rights (ECHR) arise by virtue of the existence of a risk to rights.³⁵ Accordingly, even if it is uncertain that the danger will materialise, the State’s duty is ‘to take appropriate steps to counter an imminent threat’.³⁶ On the facts, given the evidence that climate change poses a real and genuine threat to the lives and welfare of Dutch citizens, and that sea level rise stands to render much of the Netherlands uninhabitable, the requirement that the State take action was held to be consistent with the precautionary principle: ‘The mere existence of a sufficiently genuine possibility that this risk will materialize means that suitable measures must be taken’.³⁷

Similarly, in Waratah Coal Pty Ltd v Youth Verdict Ltd and Ors, the Land Court of Queensland held in favour of the claimants despite an alleged ‘indirect and tenuous’ causal link between a proposed coal mine and the violation of human rights.³⁸ The Court instead accepted the claimants’ argument that there was a ‘logical and rational connection’ between the authorisation of the relevant applications and the subsequent harms caused by coal burning.³⁹ This was enough to establish a ‘sufficient causal relationship to find the act [of granting the applications] has the capacity to limit a human right’.⁴⁰ As such, the Court recommended that the applications be denied by the respective authorities.⁴¹

Human rights-based claims may also be brought against defendant corporate enterprises, drawing upon the independent responsibility of businesses to respect human rights under pillar two of the 2011 United Nations Guiding Principles on Business and Human Rights (UNGPs).⁴² The UNGPs were influential in the Milieudefensie case mentioned earlier.⁴³

16.2.4 Causation and Attribution

There is a particularly important relationship between causation and attribution, and the latter is considered in detail in the next chapter. While it is still unclear what the relationship between attribution science and legal tests of admissibility of climate models is, there is clearly an important relationship between attribution studies and the evolution of legal tests of causation.

Attribution will – and already has – been influential in establishing the causal relationship between activities, events, and harms. For example, Heede’s 2013 study has been cited in many lawsuits against carbon major corporations.⁴⁴ As outlined in Chapter 3 introducing attribution science in this Handbook, attribution studies illustrate how closely climate models have predicted extreme events and therefore how reasonably foreseeable such events have become. For example, the 2021 IPCC report lists the increased probabilities of the occurrence of extreme, one-in-fifty-year events, as temperatures increase.⁴⁵ Attribution studies can be helpful in creating a stronger causal nexus between events and harms and the emergence of best practices in causation tests.

16.3 Case Law Development – State of Affairs

This section approaches cases from a thematic as opposed to a jurisdictional lens. Here, we divide cases into those that focus on project-based emissions, on the one hand, and cases that focus on climate policy and regulation, on the other.

16.3.1 Project-based Cases

The cases covered here involve a challenge to government action, such as a permit or licence granted for a project which plaintiffs claim will increase GHG emissions or an inaccurate or incomplete environmental impact analysis. In these cases, we find courts struggling to map climate harm onto more traditional causation-based legal tests, even in the context of human rights claims. Courts seem more comfortable asking agencies to re-examine emission assumptions and requiring them to take a cumulative approach to the direct and indirect impacts of their approvals.

In some cases, however, courts have taken a broader approach to causation. Instead of requiring a finding of a causal nexus between actions and harms, they focus on establishing a reasonably foreseeable risk of harm. Some cases in this category have grappled with the indirect effect of CO₂ emissions from permit approvals, sometimes in conjunction with an assessment of local cumulative effects. Government agencies may struggle to account for indirect or scope 3 emissions from permits granted for extraction, for example. In addition, these cases may involve questions about hypothetical emissions which may occur absent judicial intervention.

Australian courts have been active contributors to the evolving jurisprudence on cases focused on project-based emissions. The 2006 decision Gray v Minister of Planning provides an early example of a successful challenge to a large coal mine under an environmental assessment process.⁴⁶ The applicant argued that GHG emissions from coal burning (scope 3) should be considered in the environmental assessment. Judge Pain agreed, holding that the GHG emissions should not be ignored despite the existence of many contributors globally and a

sufficient proximate link between the mining of a very substantial reserve of thermal coal in NSW [New South Wales], the only purpose of which is for use as fuel in power stations, and the emission of GHG which contribute to climate change/global warming, which is impacting now and likely to continue to do so on the Australian and consequently NSW environment.⁴⁷

In reaching its decision, the court identified the failure of the administrative decision-maker to ‘take the principle of intergenerational equity into account’, which was a legal requirement under the relevant legislation.⁴⁸

In a 2016 case from Kenya, Save Lamu v Republic of Kenya,⁴⁹ an NGO successfully sued for a new environmental impact assessment (EIA) process due to lack of public participation, as well as omissions from the EIA for a coal-fired power plant on climate emissions and mitigation efforts. The National Environmental Tribunal found that due to the great importance of climate change issues, the EIA was incomplete and inadequate, particularly in the face of failures of the EIA to comply with the 2016 Climate Change Act, and the impact of the emissions on surrounding communities.

In the Center for Biological Diversity v U.S. BLM,⁵⁰ a Colorado court remanded the Bureau of Land Management’s approval of a master development plan for natural gas wells and pads back to the agency on the basis that the agency’s consideration of the approval was insufficiently narrow. The agency had failed to take a hard look at the severity of the impacts of GHGs that would result from its approval and the cumulative impacts of the emissions on air and water quality. The court found that combustion emissions would be an indirect effect of the agency’s decision and the agency’s approval (which did not consider these emissions) was arbitrary and capricious in that it failed to take a hard look at the foreseeable indirect effects of that combustion. In a corollary finding, the US Court of Appeal in the 7th circuit in Zero Zone Inc v U.S. DoE (2016)⁵¹ found that the Department of Energy’s consideration of indirect benefits, such as carbon reductions and the global benefit of GHG reductions, was not arbitrary and capricious.

In the 2019 Australian decision Gloucester Resources Limited v Minister for Planning,⁵² the proponent appealed the Minister for Planning’s refusal to grant development consent for the Rocky Hill Coal Project.⁵³ In considering the impacts of climate change, the court observed that: ‘All of the direct and indirect GHG emissions of the Rocky Hill Coal Project will impact on the environment. All anthropogenic GHG emissions contribute to climate change’.⁵⁴ Chief Justice Brian Preston explicitly referred to causation, stating:

There is a causal link between the Project’s cumulative GHG emissions and climate change and its consequences. The Project’s cumulative GHG emissions will contribute to the global total of GHG concentrations in the atmosphere. The global total of GHG concentrations will affect the climate system and cause climate change impacts. The Project’s cumulative GHG emissions are therefore likely to contribute to the future changes to the climate system and the impacts of climate change. In this way, the Project is likely to have indirect impacts on the environment, including the climate system, the oceanic and terrestrial environment, and people.⁵⁵

Notably, the court referred not only to the causation analysis in previous Australian jurisprudence⁵⁶ but also to Massachusetts v EPA⁵⁷ and the decisions of the Dutch District Court⁵⁸ and Court of Appeal⁵⁹ in the Urgenda litigation.⁶⁰

In Sharma, eight Australian children brought a representative action against the Commonwealth Minister for the Environment seeking an injunction to stop the approval of the Whitehaven Vickery coal mine.⁶¹ The children argued that the Minister owed a duty to take reasonable care not to cause them personal injury when exercising her statutory power to approve or not approve the extension of an existing coal mine. The first instance court agreed, holding that a reasonable Minister ‘ought to have the children in contemplation when facilitating the emission of 100 MT of CO₂ into the atmosphere’.⁶² The court rejected the Minister’s argument that she did not have control over each point in the causal chain,⁶³ holding instead that the Minister had conflated reasonable foreseeability and control, creating a requirement that there be a ‘causal nexus between conduct and injury’ instead of a real, reasonably foreseeable risk of harm.⁶⁴

On appeal the judges of the Full Federal Court unanimously overturned the earlier decision but for different reasons.⁶⁵ All three judges were challenged to disaggregate the duty of care, causation, and damages enquiries.⁶⁶ According to Chief Justice James Allsop, disaggregating the duty of care from damage removes the duty from the ‘very essence of the cause of action’, with the plaintiffs seeking to impose the duty ‘decades before any foreseeable harm which could have any connection whatsoever to the act in question’ and ‘decades before one knows whether there will be a cause of action’.⁶⁷ The reasonable foreseeability enquiry, Chief Justice Allsop suggested, ‘has a causal element: The reasonable foreseeability is of the negligent act or omission causing or materially contributing to the harm’.⁶⁸ Justice Michael Wheelahan similarly held that the foreseeability must be of an injury ‘compensable by the law of negligence and that is capable of being caused by a careless act or omission of the tortfeasor’, not a prospect of causation ‘so remote that it is far-fetched, or fanciful’.⁶⁹ Justice Jonathan Beach, on the other hand, disagreed with the conflation of causation with reasonable foreseeability, finding the initial judge’s conclusion to be sustainable:

the preponderance of authority does not demand that a legally acceptable pathway to ultimately demonstrating causation must be used in any reasonable foreseeability analysis. Moreover, who knows what the legally acceptable factual causation test will be in eighty years when a fully formed tort is likely to arise, if at all? And indeed, who knows what the science will show in eighty years in terms of factual causation?⁷⁰

Ultimately, Justice Beach suggested that the High Court of Australia would be the appropriate court to ‘engineer new seed varieties for sustainable duties of care, modifying concepts such as “sufficient closeness and directness” and indeterminacy to address the accelerating complexity, multiple links, and cross-links of causal relations’.⁷¹ However, the decision will not be appealed.⁷²

In the New Zealand private law case of Smith v Fonterra Co-Operative Group Ltd and Ors,⁷³ a Māori leader sought a declaration that the actions of some of New Zealand’s largest GHG emitters or companies that supply products that emit GHGs⁷⁴ unlawfully caused or contributed to climate change.⁷⁵ At first instance the public nuisance claim was struck due to a lack of sufficient causal link,⁷⁶ while the negligence action was struck out as the court rejected the possibility that the ‘but for’ test could be avoided in the climate context.⁷⁷ A third novel cause of action was allowed to proceed to trial.⁷⁸ The Court of Appeal rejected Mr Smith’s appeal on public nuisance and negligence and allowed it on the novel cause of action.⁷⁹ The Court reasoned that climate change is unique in that every person is both responsible for the harm and a victim of said harm;⁸⁰ the focus on ‘net zero’ created complications as it was unrealistic to suggest all GHG emissions are tortious;⁸¹ and an action against a subset of emitters is an ineffective way to address climate change,⁸² especially where the chosen defendants alone did not make a material contribution to climate change.⁸³ With regard to the negligence claim, the Court of Appeal distinguished proximity from foreseeability and was not persuaded by the argument that a sufficiently proximate relationship existed as Smith was part of an identifiable vulnerable class of plaintiffs, Northland coastal Māori, giving rise to knowledge of actual risk.⁸⁴ Moreover, despite several alternatives to the ‘but for’ test for causation being put before the court, it held that the ‘class of possible contributors is virtually limitless’ and that the inability to name or join a substantial share of contributors was a problem that could not be overcome without fundamentally changing tort law.⁸⁵ Leave to appeal to the New Zealand Supreme Court has been granted.⁸⁶

Finally, the 2020 People v Arctic Oil⁸⁷ case in the Norwegian Supreme Court illustrates the challenge of trying to intervene at the exploration stage, combined with court reluctance to account for emissions from the combustion of oil and gas after it has been exported. While the Supreme Court held that citizens are protected from environmental and climate harms under the Norwegian Constitution, the extent of emissions from exported oil and gas arising from licences for future oil and gas exploration in the Barents Sea was too uncertain to conclude they would cause the requisite harm.⁸⁸ The plaintiffs appealed to the ECtHR in 2021, arguing that the licenses violate Article 2 (right to life) and Article 8 (right to respect for private and family life) of the ECHR.⁸⁹ An outstanding question is whether the outcome of a similar decision would be different in light of the International Energy Agency’s 1.5 report⁹⁰ published in May 2021, which makes clear that there is no room for approving development in new oil and gas fields if the world is to limit global warming within the temperature goal of 1.5°C of the Paris Agreement.

16.3.2 Challenges to Policy and Regulation

Another category of cases requests policy or regulatory action by the State, either through a petition for rulemaking to a specific government agency like the US EPA or a request to the government as a whole to reduce emissions across all sectors in the future, on the basis of human rights or other claims. As described earlier, the first major US case that dealt with causation involved the State of Massachusetts submitting a petition for rulemaking to the EPA to regulate GHG emissions under the Clean Air Act as an air pollutant.⁹¹ The EPA originally denied the petition on the basis that it had no authority under the Act to address global emissions and a causal link between GHGs and increases in global surface air temperatures was not unequivocally established. The agency also claimed that any regulation would be a ‘piecemeal approach’ to climate change that conflicted with the federal government’s general approach to the issue. The agency therefore adopted a ‘drop in the ocean’ approach.

The US Supreme Court remanded the issue back to the EPA, finding that GHGs could be regulated as an air pollutant under the Act, and also dismissed the agency’s findings on causation. Justice John Paul Stevens noted that even if the changes associated with climate change were widely shared, that did not minimise Massachusetts’ interest in the outcome of the litigation. Although the agency claimed India and China would offset US emissions, the Court found the EPA ‘overstated its case’ in that regard:

Agencies, like legislatures, do not generally resolve massive problems in one fell swoop, but instead whittle away over time, refining their approach as circumstances change and they develop a more nuanced understanding of how best to proceed … And reducing domestic auto emissions is hardly tentative … The U.S. transportation sector emits an enormous quantity of CO₂ into the atmosphere … A reduction in domestic emissions would slow the pace of global emissions increases, no matter what happens elsewhere.⁹²

The case takes an incrementalist approach to emissions and the ability of regulatory action to ameliorate climate change. It is an early case that adopts a broader approach to causation. The case of Center for Biological Diversity v NHTSA in the 9th Circuit took a similar approach.⁹³ The court looked at the percentage of global emissions from US light trucks and the transportation sector overall from scientific reports. Finding those contributions to be considerable, the court held that the National Highway Traffic Safety Administration’s failure to monetise the benefits of reducing CO₂ emissions from the US automobile fleet was arbitrary and capricious.

In a more recent case against the Dutch State, Urgenda, a Dutch NGO, successfully sought an order from the court directing the Netherlands to reduce its GHG emissions by 25 per cent relative to 1990 by 2020, although it was left up to the State to determine what specific measures it would take to comply.⁹⁴ Similar to the two previous cases, the nature of the relief sought was that the State take preventative measures in the future to combat climate change. The Dutch claimants argued with reference to the State’s human rights obligations under the ECHR, specifically Article 2 (right to life), Article 8 (right to respect for private and family life), and Article 13 (right to an effective remedy before a national authority).⁹⁵ Although Urgenda could not directly invoke these rights, it was able to rely upon Article 3.305a of the Dutch Civil Code to bring the claim on behalf of Dutch residents who are the victims.⁹⁶ Drawing on ECHR case law, the Dutch Supreme Court held that where there was a ‘real and immediate risk’ of harm under Articles 2 and 8 of the ECHR, the State’s positive obligations were triggered to prevent such harm even without identifying specific prospective victims.⁹⁷ In upholding the decision of the Court of Appeal in 2019, the Supreme Court concluded ‘Articles 2 and 8 ECHR relating to the risk of climate change should be interpreted in such a way that these provisions oblige the Contracting States to do “their part” to counter that danger’.⁹⁸ The Court rejected arguments that the State should not have to comply with its partial responsibility because other States were failing to comply, or that its emissions were so small compared to others that it would make little difference globally.⁹⁹ Instead, it drew upon the carbon budget concept: each reduction ‘has a positive effect on combating dangerous climate change’ as it leaves more room in the budget.¹⁰⁰ Similar to the US cases earlier, in Urgenda the Court adopted an incrementalist approach to amelioration of climate change – that every emission counts.

In the Canadian case of Mathur v Ontario, brought by seven young Canadian citizens against the province of Ontario, a motion to strike was refused.¹⁰¹ The Cap and Trade Cancellation Act at the heart of this case effectively reduced Ontario’s GHG reduction target as under previous legislation. The plaintiffs pointed out that, per the Paris Agreement, parties must progressively strengthen their emission targets over time – not weaken them.¹⁰² Ontario had alleged that the appellants’ assertions of harm were based on a ‘chain of speculative assumptions’, including that other provinces and countries could offset a lack of ambition in Ontario’s GHG targets, and that catastrophic climate impacts could not be avoided by Ontario increasing its targets.¹⁰³ The Court was unpersuaded by these arguments, and took a progressive approach to causation and the harm alleged.¹⁰⁴ The Court adopted the Supreme Court’s more flexible standard of causation – ‘sufficient causal connection’ – which allows the circumstances of each particular case to be taken into account. It does not require that government-impugned conduct be the only or dominant cause of prejudice but is satisfied by a reasonable inference drawn on the balance of probabilities, sensitive to the context of the particular case. This flexible text also encourages the use of expert witnesses and social science evidence,¹⁰⁵ and it takes a broader approach to causation.

Two cases modelled on Urgenda have arisen in France, one brought by an NGO and the other by a municipality. In the former case, Notre Affaires à Tous brought action against the French government, alleging that its failure to take sufficient action against climate change was a breach of its statutory duty to act under domestic and international law.¹⁰⁶ In February 2021, the Administrative Court of Paris found a causal link between the French government’s inaction in relation to GHG emissions and ecological damage even though it only comprised one part of the damage.¹⁰⁷ The Court ordered the government to disclose and justify its measures to achieve its GHG reduction targets.

Similarly, the community of Grande-Synthe and others brought action against the French government for their alleged failure to take sufficient action to reduce GHG emissions.¹⁰⁸ The claimants argued that this failure to act violated domestic and international law, including the ECHR, Paris Agreement, French Environmental Code, and the French Charter for the Environment. The Court found that this was justiciable, partly due to the fact that Grande-Synthe is a coastal town that is particularly susceptible to the adverse effects of climate change,¹⁰⁹ and held that the government’s failure to take useful measures towards their climate commitments caused harm to the claimants. In 2020, the Council-d’Etat referred the issue back to the government and required them to justify their means of meeting climate commitments (40 per cent reduction in GHG emissions based on 1990 levels by 2030). In 2021, the Council d’Etat ordered the government to ‘take all measures necessary’ by the end of March 2022 to reduce GHGs and meet their climate commitments.¹¹⁰

16.4 Emerging Best Practice in Causation

There is a significant amount of jurisprudence on causation. As established in 3.1, cases that challenge project approvals offer an important opportunity to stop fossil fuel extraction and future emissions. Courts that adopt an indirect test of reasonable foreseeability of harm offer examples of best practice (e.g. Gloucester Resources). Unfortunately, courts in other similar cases continue to struggle to move beyond direct but-for causation analysis and the view that evidence of actual damage is essential, which is a highly problematic approach given the temporal and spatial dimensions of GHG emissions and resulting harms.

As established in 3.2, prevention-focused cases in the public law arena, where plaintiffs sue to prevent or reduce future emissions are the area of jurisprudence where an incrementalist and less stringent approach to causation has found the most success, illustrating emerging best practice (e.g. Massachusetts, v EPA, Urgenda, Notre Affairs a Tous, and Grande-Synthe). Plaintiffs point to the contributions that State-based emissions make to global emissions and, in conjunction with the Paris Agreement and latest scientific reports, convince judicial bodies that future emission reductions are important and closely connected to preventing future harm. In countries with robust human rights frameworks, such as in the European Union, this broader approach to causation has found the most judicial success.

Emerging best practices in causation acknowledges that traditional tort-related tests are insufficient, and fall short when the complexity of climate change and the inability to identify a concrete nexus between actions and harms is used by the judiciary as a limitation to the finding of causation. We identify this limited approach to causation as a ‘drop in the ocean’ approach – that any reduction in emissions by the defendant (being a State or non-State actor) will have limited or no effect on the harms experienced now, or to be experienced in the future, by the plaintiff.

Emerging best practices, in our view, does not apply the ‘drop in the ocean’ approach. Instead, it considers and applies a broader, more general approach to causation on the basis of newly evolving and best-available science and attribution studies. These judicial findings predominantly rely on collective goals articulated in the Paris Agreement and dismiss arguments that emissions from one company or country are not effective in addressing global climate change. Instead, judges rely on arguments that every emission reduction counts, with reference to recent IPCC and other scientific reports, and accept that these harms can be supported by science. Indeed, the ‘drop in the ocean’ approach has been explicitly rejected in many cases.¹¹¹ In our view, as more and more of these scientific reports are published, more examples of these best practices will appear throughout climate litigation cases.

Once impacts within a country can be linked to global emissions, courts are more willing to consider national impacts as affecting and causing harm to plaintiffs. Emerging best practices draw broader causal inferences between GHG emissions, large emitters, and effects on the ground, and therefore elaborate on the traditionally narrow strictures of the cause-and-effect relationship in law. Prevention-oriented cases, including cases involving public law and government action, tend to apply a less stringent test to establish causation. These cases specifically avoid or reject the ‘drop in the ocean’ approach and therefore broaden the causal quality of the law to introduce more conceptual relationships, adding an element of fairness but also uncertainty into the law. While a broader approach to causation is welcome, it does mean that it is unclear how much or little emissions will be considered to add to the problem of climate change.

Another emerging trend is the growing litigation against corporations in the climate context, which at times employs this broader causal relationship. This is evidenced both in the human rights context for direct harms, and in the investor-related context in relation to financial losses.

An example of innovative causal relationships is highlighted in the Philippines’ Human Rights Commission’s investigation and final report.¹¹² The Commission found that a State is not absolved of its duty to protect against climate change impacts by the lack of a clear causal relationship between GHGs and climate change impacts. Further, the Commission established that not only carbon major companies but all enterprises along their respective value chains may be found responsible for human rights violations as a result of climate change impacts.

Unlike traditional litigation efforts, the Commission does not attempt to pin legal liability for damage on corporations. Rather, the investigation serves largely as an expository exercise to highlight the damaging role these entities play in the context of climate change. Using law as an expository tool in this way overcomes the causation hurdles experienced in traditional litigation against carbon major companies, and it can be equally effective in connecting the activities (and profits) of these entities with the human suffering that has been and will continue to be caused by climate change.¹¹³

The Commission’s approach does, however, raise questions over causal relationships. The investigation’s outcome is unable to trace a direct route between individual corporate emissions and concrete human rights harms. Instead, it provides a more nuanced and generalist approach, finding that corporations played a clear role in anthropogenic climate change and its attendant impacts. The Commission found that, based on the evidence, carbon major companies could be found legally and morally liable for human rights violations arising from climate change in certain circumstances. These focused on circumstances involving obstruction, deception, or fraud, where the relevant mens rea (criminal intent) may exist to hold companies accountable under not only civil but criminal laws. This is an example of using causal inferences but tying them to specific legal responsibilities.

One especially innovative aspect of the Philippines investigation is the reliance placed by the plaintiffs upon the business responsibility to respect human rights of the UN Guiding Principles in framing the responsibilities of the carbon majors.¹¹⁴ Of particular relevance to causation is Principle 13:

The responsibility to respect human rights requires that business enterprises:

1. (a) Avoid causing or contributing to adverse human rights impacts through their own activities, and address such impacts when they occur;

2. (b) Seek to prevent or mitigate adverse human rights impacts that are directly linked to their operations, products or services by their business relationships, even if they have not contributed to those impacts.

This conception of value chain responsibility, which acknowledges that business enterprises do not have full control over all aspects of their supply and value chains, provides a pragmatic framework from which to consider causation. Notably, the Commission further confirmed the responsibility of all entities within the value chain of carbon majors to remedy harms that they have caused or to which they have contributed in accordance with Principle 22 of the UNGPs.¹¹⁵

While the Philippines investigation was trailblazing for invoking the UNGPs, the 2021 Milieudefensie decision takes things a step further by clearly linking the UNGPs with the Paris Agreement targets, reinforced by reference to Shell’s practices including reporting across scopes 1–3 in accordance with the GHG Protocol. The court considered at length the independent responsibility of business to respect human rights under the UNGPs as a global standard of expected conduct of all businesses wherever they operate, which requires companies to avoid causing or contributing to human rights impacts through their own activities, and to prevent and mitigate those arising from business relationships encompassing the entire value chain.¹¹⁶

Royal Dutch Shell (RDS) is the top holding company of the Shell group, comprising over 1,000 separate companies established and operating in over 150 countries around the world.¹¹⁷ The plaintiffs sought to order RDS ‘to limit or cause to be limited the aggregate annual volume of all CO₂ emissions into the atmosphere (Scope 1, 2, and 3) due to the business operations and sold energy products of the Shell group’ by at least 45 per cent relative to 2019 levels.¹¹⁸ To do so, the plaintiffs relied upon the unwritten standard of care in the Dutch Civil Code, to be interpreted using human rights and ‘soft law’ instruments including the UNGPs, the UN Global Compact, and the Organisation for Economic Co-operation and Development (OECD) Guidelines for Multinational Enterprises.¹¹⁹

The court explored the ‘distinctive aspects of responsibility for environmental damage and imminent environmental damage’ with regard to climate change in the Netherlands and the Wadden region and how these distinctive aspects must inform the interpretation of ‘event giving rise to the damage’ under Article 7 of Rome II:¹²⁰ ‘[E]very emission of CO₂ and other [GHGs], anywhere in the world and caused in whatever manner, contributes’¹²¹ to climate harms, and these only cause damage or imminent damage in conjunction with other emissions. Despite Article 7’s reference to a single event, ‘it leaves room for situations in which multiple events giving rise to the damage in multiple countries can be identified’ and the Shell group corporate policy ‘therefore constitutes an independent cause of that damage’.¹²²

16.5 Replicability

As illustrated earlier, broader approaches to causation, found in early cases such as Massachusetts v EPA, have been adopted in an increasing number of jurisdictions. Indeed, several jurisdictions have explicitly rejected the ‘drop in the ocean’ approach in policy cases focused on prevention. Some courts have been influenced by this to adopt an indirect reasonable foreseeability of harm approach. This suggests that other countries, when deciding cases against government agencies for permitting decisions or when demanding government action, could also reject the ‘drop in the ocean’ theory and adopt a broader approach to causation. This may mean more robust decisions around emissions reductions, particularly in light of State-based commitments under the Paris Agreement and its global temperature goals as well as recent IPCC scientific reports that support the broader approach to causation. Emerging scientific and attribution reports could support generalisable principles that promote the broader approach – that the defendant’s conduct contributed significantly to the plaintiff’s harms. However, this may be more difficult in cross-jurisdictional claims involving foreign plaintiffs even where they have been granted standing.

A different question is whether cases that approach causation through a human rights lens are easily replicable in States that are both less engaged with regional human rights mechanisms and lack an enumerated human right to a clean, healthy, and sustainable environment in their Constitution (for example, Canada and the US). The 2022 United Nations General Assembly (UNGA) resolution recognising the right to a clean, healthy, and sustainable environment may create opportunities to inform climate causation with human rights in all States, especially in light of the voting record of 161 in favour with only eight abstentions.¹²³

Reliance on the business responsibility to respect human rights as an international legal expectation to inform the interpretation of tort doctrines or other causes of action may be increasingly replicable across jurisdictions, with implications for the causation analysis. Beyond their endorsement by the UN Human Rights Council is the increasing evidence of their influence in courts and international fora.¹²⁴ Indeed, the UNGPs are also explicitly recalled in the UNGA resolution on the right to a clean, healthy, and sustainable environment. An additional source of UNGPs influence, also cited in RDS and by the Philippines Commission, is the OECD Guidelines for Multinational Enterprises, which added a chapter regarding the business responsibility to respect human rights in 2011 and was updated in 2023. This responsible business conduct guidance is backed by over fifty adhering States, including many that are home States to multinational fossil fuel companies. Together with the environment chapter and interpretations on climate-related matters provided by OECD National Contact Points in adhering States, the human rights-related climate responsibilities of enterprises are becoming increasingly clear, especially for multinationals that also adhere to carbon disclosure initiatives for emissions across scopes 1–3 like the GHG Protocol.

16.6 Conclusion

Causation arguments arise in many different kinds of climate litigation and at different stages from standing to tort. Cases that challenge project approvals offer an important opportunity to stop fossil fuel extraction and future emissions, yet many courts struggle to move beyond direct but-for causation analysis despite best practices that adopts an indirect test of reasonable foreseeability of harm. An emerging concern may be attention given by courts to net-zero commitments (e.g. Smith), which muddies the waters when it comes to accepting that fossil fuel extraction necessarily leads to problematic scope 3 emissions.

Cases where plaintiffs sue to prevent or reduce future emissions stemming from government policy or regulation are clearly ripe for a broader approach to causation, and this area is where an incrementalist approach to causation has found most success. Cases such as Massachusetts v EPA, Urgenda, Notre Affairs a Tous, and Grande-Synthe all illustrate emerging best practices. Plaintiffs can point to the contributions that State-based emissions will make to global emissions and, in conjunction with the Paris Agreement and latest scientific reports, are able to convince judicial bodies that future emission reductions are important and closely connected to preventing future harm. In countries with robust human rights frameworks, such as in Europe, this broader approach to causation is finding the most judicial success. This is a key trend which we anticipate will continue. Where courts adopt a broader, best practice approach to causation, litigation can make a real difference both nationally and internationally in stemming the most catastrophic impacts of climate change.

We anticipate that human rights-based claims against corporate enterprises will increase, building on the approach to value chain causation in the UNGPs and emerging best practice cases. Disclosure-based claims are likely to be most easily successful. Plaintiffs will point to portfolio losses tied to reserve write-downs, or, in the case of utilities, infrastructure losses and/or litigation tied to damage, and the lack of disclosure of these risks by companies. Bankruptcy law is likely to be another area of law where causal relationships between climate-related risks and impacts, and bankruptcy will receive attention.¹²⁵ We also anticipate that climate litigation in the Global South, with State-owned enterprises as defendants, is likely to emerge, given the large emissions contributions these entities have made and continue to make. Causation in these instances may be easier to prove, given the large emissions and the State-sanctioned nature of corporate activities.

17 Climate Causality From Causation to Attribution

Petra Minnerop ^*

17.1 Introduction: Objectives and Context

Climate law and governance structures evolve through different instruments, in international, regional, and domestic law and policy. A significant mode of development is jurisprudential. Courts often make authoritative statements not only about the law on climate change but also about the underlying scientific evidence. At the heart of this growing field of climate jurisprudence are almost always legal concepts that were neither designed nor intended for the application in the context of a collective action problem. Therefore, judicial pronouncements on law’s core concepts reveal how the law is challenged by, and grapples with, climate change, especially where clarifying legislation is absent. Apart from filling legislative gaps and developing the law, courts also influence the societal perception of climate change, including its causes, impacts, urgency, and legal implications. Analysing these judgments structures, consolidates, and develops the law on climate change.

This chapter provides a thorough analysis of some of the most significant cases on causation and attribution in a rapidly growing field of global climate jurisprudence. To structure the analysis, I situate the legal notion of attribution within an overarching concept of climate causality that comprises general causation, specific causation, and attribution as a sequence of analytical steps. While general and specific causation are primarily concerned with identifying the factual relations between cause(s) and event(s), attribution adds a distinct normative dimension.¹

The approach in this chapter addresses the interdisciplinary challenge of applying law in the context of climate change, connects attribution in law with event attribution, and explains the inductive and deductive approaches used in scientific studies. The case law is selected from a range of different legal orders, for its contribution to advancing the concept of climate causality. To structure the vast number of relevant cases, the chapter offers a novel system based on thematic areas where jurisprudence emerges that shapes the normative context for causal explanations and attribution. Four areas of judicial engagement with climate change are identified as main sources for transferable arguments that could inform the reasoning on attribution: the determination of the scope of relevant emissions, the review of national climate targets and measures, the permissibility of emissions-intensive infrastructure projects or activities, and courts’ readiness to use and review general (environmental) law concepts to develop climate litigation, thus expanding the normative lens.

17.1.1 Objective of This Chapter

Given that so far only a limited number of cases explicitly discuss attribution directly, the approach in this chapter is to emphasise the emerging nature of the judicial treatment of attribution with regard to climate change. Courts have made authoritative statements about the reality of climate change,² they have used reports of the Intergovernmental Panel on Climate Change (IPCC) as expert evidence,³ and they have shaped the wider normative context in which causal explanations in the field of climate change are embedded.⁴ Yet to date, attributing a specific climate-related impact to a defined emitting geographical region or an individual major emitter has been a difficult task in the court room.⁵ Compensatory claims against individual emitters remain at risk of failing the legal tests for causation and attribution across jurisdictions.⁶ Only prospectively have courts found a causal link between planned major infrastructure projects and their anticipated contributions to global emissions and to further adverse climate change impacts – as discussed in the preceding chapter.⁷

Meanwhile, a thorough analysis reveals that even a dismissed case can shed light on legal criteria for causation and attribution while pointing to the need for further legal and scientific research. An example is Comer v Murphy Oil USA, Inc, where the Court dismissed the case but alluded to the defendants’ memorandum and stated that the plaintiffs would need to demonstrate the following:

1. (1) what would the strength of Hurricane Katrina have been absent global warming;

2. (2) how much of each plaintiff’s damages would have been attributable to Hurricane Katrina if it had come ashore at a lower strength; and

3. (3) how much of each plaintiff’s damages was attributable to failures by others, such as the Federal Emergency Management Agency (FEMA) and other governmental agencies, to prevent additional injury.⁸

This list of criteria merits critical evaluation. The Court’s three points may indeed not set forth a conclusive selection that fully reflects the causally relevant contribution of climate change to Hurricane Katrina. Climate change may not only have contributed to the strength of the hurricane and the resulting damages, it may also have exacerbated the failures by others, thereby amplifying existing vulnerabilities. These interdependencies between existing vulnerabilities, administrative failures, and climate change deserve attention from a scientific and from a legal point of view, to make clearer statements about causation and attribution. Exploring these factual connections should not be limited through a constricted set of criteria.

An increased focus on the intersection of science and law, where scientific research is informed by a better understanding of legal criteria for attribution, is certainly timely. Attribution-based cases represent a key trend in litigation, albeit one that is moving more slowly than originally anticipated.⁹ This may be due to the fact that the legal analysis of ‘attribution’ incorporates a normative operation: it is never purely scientific or merely counterfactual but entails the judicial determination of a factual, social, and legal reality.¹⁰ This determination will be case-specific and dependent on the relevant law. However, it can be informed by filing cases into categories derived from environmental case law beyond climate change, such as the differentiation between ‘look back’ and ‘in the moment’ cases.¹¹ The respective category defines the applicable standard for judicial intervention so that protective measures can be adopted before harm occurs, despite remaining scientific uncertainties. Therefore, and with an emphasis on the status nascendi, emerging best practices in this chapter are derived from judicial pronouncements that prune the normative context and pave the way for a rigorous and comprehensive causal analysis in future cases.

17.1.2 Climate Science and Attribution Studies as a Matter for Courts

Climate science has already become a matter for courts. Courts across a number of jurisdictions have established a causal link between increasing greenhouse gas (GHG) emissions¹² and an increasing risk of climate-related extreme events and slow-onset events.¹³ The relevant available scientific evidence is often directly derived from the reports of the IPCC, such as in Milieudefensie v Royal Dutch Shell,¹⁴ or indirectly, from national scientific advisory committees that provide independent advice and devise national carbon budget calculations based on IPCC reports.¹⁵ The Administrative Court of Berlin in German Farmers v Germany argued that there ‘is much to be said for at least an equal global per capita distribution of the remaining global CO₂ budget’.¹⁶

The physical science on climate change, and, in particular, detection and attribution studies, provides important and steadily evolving information for the causal analysis generally and for the specific criteria of legal attribution.¹⁷ Relevant studies can deliver expert evidence in court and they also more generally improve our understanding of the human contribution to extreme events,¹⁸ such as floods,¹⁹ hurricanes,²⁰ heatwaves,²¹ or slow-onset events and impacts on vulnerable ecosystems.²² The conventional approach of probabilistic event attribution uses inductive reasoning to establish a quantifiable fraction of the magnitude or probability of risk or harm that can scientifically be attributed to climate change or even localised regional emissions.²³ Studies that claim to evidence the link between a concrete climate-related impact and an individualised amount of emissions carry the potential to change the outcome of litigation.²⁴ However, only reliable, unbiased, and carefully reviewed studies can produce the legally relevant evidence through assessing observed changes in weather extremes and climate-related impacts, their attribution to causes, and their future trajectories and return periods.²⁵

The IPCC has acknowledged that case-specific studies provide evidence in addition to the ‘established fact that human-induced greenhouse gas emissions have led to an increased frequency and/or intensity of some weather and climate extremes since pre-industrial time, in particular for temperature extremes’.²⁶ The IPCC stated in its Sixth Assessment Report (AR6), Working Group I, that since the 2018 IPCC Special Report on Global Warming of 1.5°C was published, new evidence has emerged that:

[E]ven relatively small incremental increases in global warming (+0.5°C) cause statistically significant changes in extremes on the global scale and for large regions (high confidence). In particular, this is the case for temperature extremes (very likely), the intensification of heavy precipitation (high confidence) including that associated with tropical cyclones (medium confidence), and the worsening of droughts in some regions (high confidence).²⁷

The legal evaluation of these scientific insights requires judicial engagement with general and case-specific scientific evidence on climate change²⁸ and climate literacy.²⁹ The relevant scientific knowledge and the law evolve often at different time scales, and this poses challenges to the science/law intersection. A continuous, mutually informing interdisciplinary discourse is necessary. An illustrative example is Native Village of Kivalina v ExxonMobil Corp, where the link between the defendant’s emissions and the erosion of the coastal line as a result of climate change at the time of the decision was too indirect to fulfil the criteria of ‘fair traceability’ (a requirement to establish standing).³⁰ Scientists nowadays claim that it would be possible to establish a causal link between the losses claimed and the defendant’s GHG emissions.³¹

Challenges and constraints in accessing the most relevant, recent, and unbiased scientific evidence in the court of law persist.³² Any limited availability of scientific evidence in court, or the actual lack of data, cannot simply be interpreted as implying that no relevant trends exist, or that anthropogenic climate change has not contributed to the intensity and frequency of a studied event.³³ Data limitations may only indicate that either the quality or the temporal length of the case-specific data collection, or both, are not suited to provide a full and specific account for attribution.³⁴ Even then, it remains possible and necessary to analyse the factual circumstances of a case in light of the already available and steadily growing body of climate science.

Given the significant and increasing importance of climate science for legal developments, both in legislation and in litigation, Section 17.2 defines the analytical steps of climate causality and explains how attribution studies can be used for legal attribution. It then explains the potential role of normative correctives³⁵ to soften the outcome of a strict causal analysis, and points to the critical function of three, instead of just two, logical fundamentals for a coherent legal analysis. Section 17.3 identifies emerging best practices of judicial engagement with climate change that could inform legal attribution. Section 17.4 discusses the potential for replicability of these arguments and Section 17.5 concludes.

17.2 Causation and Attribution as Intertwined Legal Concepts and Attribution Studies

The differences between general and specific causation and attribution are not always clearly articulated, and the terminology varies between science (discussed in Chapter 3) and law. Furthermore, some statements about causation in law imply attribution, and there are different approaches to distinguish ‘event’ and ‘source’ attribution in scientific studies.³⁶ In human rights-based cases, a general causal link between a country’s projected GHG emissions, increasing global mean temperatures, and expected impacts of climate change that risk interfering with individual rights may be sufficient to argue that national climate targets are inadequate (see Chapter 7).³⁷ By contrast, in cases that seek to establish individual liability for a climate-related event, specific causation, and attribution of the harm or increased risk of harm, to the action or omission of the defendant must be demonstrated. It has been noted in 2018 that, for the first time, attribution science opens the door to establishing ‘the evidence of specific and quantifiable loss and damage arising out of atmospheric levels of anthropogenic GHGs that can be linked to specific regions and individuals’.³⁸

17.2.1 Attribution as a Scientific and Legal Field of Study

Event attribution as a field of scientific study is defined as ‘the process of evaluating the relative contributions of multiple causal factors to a change or event with an assignment of statistical confidence’.³⁹ A number of different analytical tools are employed, spanning climate observations, modelling, and statistical (re-)analyses.⁴⁰ These attribution studies provide the ‘human contribution assessment’ for observed changes in ecosystems,⁴¹ such as ocean heat content increase or arctic sea ice loss – cases where since 1970 anthropogenic emissions have become the main drivers for those changes.⁴² Scientists identify changes in characteristics of the climate system, such as trends and variations in single extreme events, including their frequency, intensity, and duration.⁴³

As a scientific field of study, attribution science is relatively young. One of the first attribution studies concerned the human contribution to the European heatwave of 2003.⁴⁴ The study found that it was very likely (confidence level >90%) that human influence had at least doubled the risk of a heatwave exceeding a threshold for mean summer temperatures in Europe.⁴⁵ The IPCC recognised for the first time in its Fourth Assessment Report (AR4) of 2007 the relevance of the data of formal detection and attribution studies as a further source for the understanding of the physical science basis of climate change, in addition to climate records and observational data.⁴⁶ Since then, evidence of observed changes in weather extremes such as heatwaves, heavy precipitation, droughts, and tropical cyclones, ‘and in particular their attribution to human influence’, has been significantly strengthened; most recently in AR6.⁴⁷

As introduced in Chapter 3 on Attribution Science, two main methodological approaches can be differentiated: probabilistic event attribution studies and the so-called storyline approach. Probabilistic attribution studies employ inductive reasoning and ask two main questions.⁴⁸ First, whether the likelihood or strength of an event has changed in the observational record, and second, whether this change is consistent with the anthropogenic influence as found in one or more climate models.⁴⁹ These climate models compare the world with climate change with the counterfactual world where no climate change exists, thereby assessing the fraction of the attributable risk that can be assigned (quantitatively and qualitatively) to anthropogenic climate change.⁵⁰

The so-called storyline approach is mainly deductive. Studies using this approach do not assess the change of likelihood in a specific event’s occurrence (they take that change as a given), but ask whether the impact of the particular event was affected by known changes (induced by climate change) in the climate system’s thermodynamic conditions.⁵¹ Thus, the focus rests primarily on specific qualitative changes in the studied event that can be attributed to climate change.⁵² From a legal perspective, both approaches can provide complementary evidence for causation and attribution.⁵³

A further layer is added by differentiating between event attribution and source attribution. Source attribution concerns the nexus between a certain activity, a project, or another defined source of emissions, and the additional and quantifiable amounts of emissions.⁵⁴ An example are wetland emissions and atmospheric sink changes that explain the growth of methane.⁵⁵

For the purpose of this chapter, and with a view to capture the relevant scientific findings of event attribution studies, the meaning of legal attribution is defined within the broader concept of climate causality that involves general causation and specific causation as a sequence of analytical steps. General causation means that a factor has altered the probability of the occurrence of a certain class of events in a statistically significant way.⁵⁶ This could encompass the general link between human-caused climate change that is affecting many weather and climate extremes in every region across the globe,⁵⁷ or between increasing human-caused climate change and heavy precipitation associated with tropical cyclones.⁵⁸ Specific causation describes the factual finding that a factor (e.g. increasing GHG emissions, increasing mean temperatures) has altered the specific characteristics of a concrete event (e.g. the duration, frequency, and/or intensity of a heatwave in a certain region and year) in a statistically significant way.⁵⁹ In the legal assessment, general and specific causation rely on counterfactual inquiries that seek to identify if, and to what extent, the factor was either necessary or sufficient for the studied event(s).⁶⁰ Neither general nor specific causation stipulates that the factor, i.e. the amount of emissions over a certain period of time, must be the only cause. There can be a set of factors that act as concurrent causes.⁶¹ It is a related but different question to measure and objectively quantify the contribution of each cause.

On that basis, attribution in law is understood as the final step that describes the adequate and quantifiable contribution of an individualised factor or activity to the studied event (impact or damage), in a specific normative context.⁶² It asks, for example, if the changed characteristics of a concrete event (increased outburst flood hazard of a glacial lake) have not only been caused by human-induced glacier retreat (i.e. specific causation between glacier retreat and increased risk)⁶³ but can be adequately assigned to a concrete human contribution. Attribution spans the nexus between the human activity and the concrete adverse impact. The term ‘adequate’ has its roots in the ‘theory of adequate causation’⁶⁴ and indicates that there can be causal chains that – for various reasons – cannot or no longer be linked to a particular source.⁶⁵

The normative considerations that are relevant to establish legal attribution will depend on the circumstances of each case and relevant scientific and legal determinations such as the role of natural variabilities, the distribution of risk spheres, and provisions concerning the onus of proof.⁶⁶ Absolute certainty is not required to prove either causation or attribution in law.⁶⁷

Within the normative evaluation of ‘adequacy’, the law – and courts in interpreting and applying legal criteria – can attribute climate-related impacts to human-controlled emissions and thereby (re-)allocate responsibilities, potentially beyond the strict ‘but for’ analysis albeit within the rule of law. However, these legal determinations can work in both ways: they can either interrupt or expand the causal chain, that is, exclude or include certain factors as causes.

An example of the former is the exclusion of so-called ‘cruise emissions’ from the consideration of an airport expansion in Vienna-Schwechat Airport Expansion.⁶⁸ The Austrian Constitutional Court interpreted the requirement for airline operators to comply with EU emissions monitoring and reporting schemes⁶⁹ so as to conclusively assign the responsibility to manage so-called ‘cruise emissions’ to airlines and not to airports or airport operators.⁷⁰ On that basis, the Court overturned an earlier decision of the Austrian Administrative Court.⁷¹ The Administrative Court had refused to grant permission for a third runway extension with the argument that the public interest of ‘no further significant increase in GHG emissions in Austria due to the construction and operation of the third runway’ prevailed over the interest to expand the airport’s capacity.⁷² The Constitutional Court did not deny that additional emissions would occur; however, it found that these had wrongly been included in the consideration of relevant public interests by the Administrative Court, given that the majority of predicted emissions would occur as cruise emissions – thus falling within the responsibility of airline operators.⁷³

The Constitutional Court’s reasoning in this case demonstrates the normative operation that furnishes attribution, and it illustrates how important it is to clearly distinguish between a factual consideration of a proposed project’s future emissions and assigning legal responsibility for those emissions. Specific causation captures the quantifiable emissions resulting from the expansion of the airport; these would not exist ‘but for’ this individual project. The next analytical step relates to the attribution of these additional emissions. It is indeed a legal determination to attribute cruise emissions to the airline operators. This legal attribution and the assigned responsibility that comes with it in terms of accounting and reporting, and possibly ‘off-setting’, are to be distinguished from specific causation, as the factual assessment of the amount of predicted emissions. According to the relevant Austrian law, the evaluation and balancing of the various ‘public interests’ affected by the project depend precisely on the factual consideration of the project’s emissions,⁷⁴ not on the legal attribution of these emissions.

Interestingly, the Philippines Commission on Human Rights included in its National Inquiry on Climate Change Report a section on ‘Recommendations for the Judiciary’.⁷⁵ Therein, it noted that ‘in many jurisdictions, courts evaluate evidence linking actors to climate-related losses using the stringent standards of legal causation’.⁷⁶ According to the Commission, ‘this disregards the work of climate and attribution science, and causes more climate injustices’.⁷⁷ The Commission proceeded to define event attribution as to establish ‘(i) whether the likelihood or strength of a natural event has changed in the observational record, and (ii) whether this change is consistent with the anthropogenic influence as found in one or more climate models’.⁷⁸ This statement confirms that measurable changes in the likelihood of an event’s occurrence or strength are legally relevant.⁷⁹

It should be mentioned that in exceptional circumstances, beyond the context of climate litigation, courts have acknowledged that normative considerations can also function in the opposite direction and draw factors in as factual causes. These are cases where a mechanistic causal analysis was found to be ‘in contradiction to law’s function to achieve justice and fairness’.⁸⁰ For example, in asbestos litigation, courts have attributed harm to the actions or omissions of the defendant, even when the traditional causal tests of ‘but for’ and ‘conditio sine qua non’ have failed.⁸¹

This interpretative approach stresses the fundamental role of the judiciary in the evolution and affirmation of so-called ‘normative correctives’ that form part of the legal concept of attribution.⁸² However, specific normative correctives in the context of climate change are not yet widely articulated or accepted. Therefore, the attribution of a specific climate risk, damage, or loss involves not only a variety of forensic, evidentiary, and legal questions, it fundamentally still proceeds in the shadow of a yet unresolved ethical debate of global climate equity and fairness.⁸³

17.2.2 Normative Correctives v Extended Logical Fundamentals?

As the Philippines Human Rights Commission remarked, an overly stringent application of causal tests will not easily be reconciled with the evidence produced by attribution studies.⁸⁴ Research has demonstrated that two main approaches are available to soften the outcome of a strict causal analysis in specific cases of alternative or hypothetical causation in multi-stage scenarios.⁸⁵ One option would be to apply in the context of climate change normative correctives, given that factual circumstances can make it just as difficult as in medical exposure cases to establish causation across a set of multiple factors. So far, these normative correctives in some jurisdictions have included considerations of fairness, distributive justice,⁸⁶ and the allocation of risk spheres between the claimant and the defendant.⁸⁷ Similarly, courts have used the ‘material contribution to risk’ test in situations where the plaintiff was unable to establish the exact contribution of a particular tortfeasor.⁸⁸ Applying these correctives has changed the outcome of the analysis in situations of alternative, hypothetical, or concurrent causation.⁸⁹

This type of an outcome-correcting approach is, therefore, neither foreign to the law nor has it been widely rejected as conflicting with a positivist approach to the law. For some specific case categories, legal provisions across a number of jurisdictions even set aside the strict rule of the ‘but for’ test.⁹⁰ For example, if a tort has been committed jointly, each tortfeasor will be liable for the full damage if it cannot be established who exactly caused the injury or damage.⁹¹ Meanwhile, normative correctives have had a lesser bearing on climate jurisprudence and the causal analysis in relation to complex climate-related extreme events that are often characterised through combined contributions of natural and human-induced factors.⁹²

An alternative option to reflect the scientific evidence of attribution studies through attribution in law is therefore to extend the logical fundamentals upon which the legal analysis of the ‘but for’ test rests.⁹³ This can be achieved by using three instead of the usual two logical fundamentals to reflect the contributory nature of concurrent causes in a set of conditions.⁹⁴ A coherent causal analysis in these multi-factor causation scenarios over a range of factors can be based on necessity, sufficiency, and, in addition, sustenance.⁹⁵ Sustenance accounts for the capacity of a factor to produce and maintain the event, even if the factor is only one among others in a set of conditions, provided its relative contribution can be objectively measured.⁹⁶ The case-specific causal analysis on sustenance will be influenced by our general understanding of the physical science basis of climate change and the evidence for the human contribution to certain types of extreme events. This general causal knowledge is captured by the novel concept of the distinctive causal field that encompasses certain types of events with common characteristics (i.e. heatwaves in a specific geographical region).⁹⁷ The distinctive causal field forms the backdrop for the assessment of the case-specific evidence, for example, concerning the occurrence of a concrete heatwave in the specific geographical region.

Recent scientific research buttresses the validity if not the necessity of the distinctive causal field for assessing scientific evidence, in arguing that attribution studies often contain far more information, ‘about other hazards of the same type, than is currently utilised’.⁹⁸

The case against the German energy provider, Lliuya v RWE, currently pending in the Higher Court of Appeal in Hamm, Germany, could be one of the first cases to illustrate how emissions could qualify as a cause for an increased flood risk on the basis of sustenance and within the context of scientific evidence on glacier melting. Two scientific studies (one using probabilistic event attribution (inductive) and one using the storyline (deductive) approach) assessed the increased outburst flood hazard from Lake Palcacocha in the context of human-induced glacier retreat.⁹⁹ At the time of writing, the legal attribution of this flood risk to a so-called ‘carbon major’, the largest German energy provider RWE, is being considered at the evidentiary stage.¹⁰⁰ This means that the Court was convinced that the case is conclusively argued from a legal point of view.¹⁰¹

17.3 Emerging Best Practice on Climate Causality in Global Climate Jurisprudence

Climate change has undoubtedly moved from the future to the present.¹⁰² The IPCC AR6, WG III Report underlines that the continuation of policies implemented by the end of 2020 – without further strengthening – will lead GHG emissions to continue to rise beyond 2025 and to a median global warming of around 3.2°C by 2100.¹⁰³ All government institutions, including courts, play a critical role in strengthening policies that incentivise emissions reductions, and emerging best practices of global climate jurisprudence can support States’ ambition.

While there has been a sharp increase in climate cases and strategic litigation in more recent years, climate jurisprudence is not a new phenomenon. One of the earliest cases to mention carbon dioxide (CO₂) emissions as a causal factor for environmental degradation is the 1998 Minnesota Court of Appeal’s opinion in re Quantification of Environmental Costs.¹⁰⁴ New litigation strategies are informed and shaped by the outcome of previous ‘waves’ of cases.¹⁰⁵

A whole new field of global climate jurisprudence has emerged since then where boundaries between jurisdictions and traditional lines of differentiation along the public/private law divide have become less suitable to systematise case categories and to derive knowledge from judicial engagement with climate law and science. Private law norms are applied in cases against States, and, equally, private actors’ duties are reconciled with States’ duties that flow from the Paris Agreement’s long-term goals.¹⁰⁶ Some cases are directly concerned with climate causality whereas others advance the normative framework in which causal explanations and attribution could evolve in the future. Therefore, the following devises an analytical structure based on four reference areas where judicial engagement with the climate challenge start to produce transferable arguments across jurisdictions. First, the determination of the scope of relevant emissions; second, the review of national climate measures and their effect on the global climate; third, the planning of emissions-intensive infrastructure projects or activities; and fourth, the use of general environmental law concepts to develop climate law.

17.3.1 The Determination of the Scope of Relevant Emissions

A critical starting point is to establish which emissions, and over which periods of time, should be included in the judicial consideration. In Urgenda, the Supreme Court of the Netherlands confirmed that all emissions are causal for further climate change, thereby opposing the ‘drop in the ocean’ argument of the government.¹⁰⁷ The logic of a limited global carbon budget that demands full consideration of all GHG emissions has also been confirmed by the New South Wales Land and Environment Court in Gray v The Minister for Planning¹⁰⁸ and in Gloucester.¹⁰⁹

In a similar vein, the Supreme Court of Norway stated in Nature and Youth Norway and Greenpeace Nordic v The State that GHG emissions from combustion of oil and gas (so-called downstream or scope 3 emissions) from exploration of the Barents Sea could interfere with the right to a healthy environment under Article 112 of the Norwegian Constitution.¹¹⁰ However, the final conclusion of the Supreme Court was based on the premise that the State could nevertheless formulate its climate policy in the light of the ‘division of responsibilities’ enshrined in international agreements.¹¹¹ This reference to international agreements led the Supreme Court to conclude that emissions from combustion would fall within the remit of the respective State using the oil and gas,¹¹² a position that risks conflating factual causation with the allocation of responsibilities for emissions accounting. The normative and/or legal attribution of these emissions, including the allocation of accounting obligations and potential off-setting responsibilities of the ‘end-user’, should be reserved for the final step in the analysis as explained in Section 17.2.

The Court of Session (Scotland) equally confirmed that excluding emissions from fossil fuel consumption from consideration as ‘direct or indirect significant effects of the relevant project’ would not render the environmental impact assessment (EIA) unlawful.¹¹³ According to the Court, these emissions stemmed from the ‘use of a finished product’.¹¹⁴

Conversely, a specific case in point that illustrates a comprehensive analysis of climate causality – including attribution – is the judgment of the Rechtbank Den Haag (District Court) in Milieudefensie v Royal Dutch Shell, where the Court explicitly included scope 1, 2, and 3 emissions in its causal analysis and ordered Royal Dutch Shell (both directly and via its legal entities which form the Shell group) ‘to limit or cause to be limited, the aggregate annual volume of all CO₂ emissions into the atmosphere (scope 1, 2 and 3 emissions) due to the business operations and sold energy-carrying products of the Shell group to such an extent that this volume will have reduced by at least net 45% at end 2030, relative to 2019 levels’.¹¹⁵ In reaching this decision, the District Court not only stated that there was a causal link between GHG emissions and dangerous climate change¹¹⁶ but also established a further causal link between the limitation of fossil fuel production and global emissions reductions. The Court found that there is a ‘direct, linear link between man-made greenhouse gas emissions, in part caused by the burning of fossil fuels, and global warming’.¹¹⁷ Thus, limiting the production of fossil fuels would result in reduction of emissions, as ‘research shows that there is a causal relationship between production limitation and emission reduction’ and ‘studies using elasticities from the economics literature have shown that for oil, each barrel left undeveloped in one region will lead to 0.2 to 0.6 barrels not consumed globally over the longer term’.¹¹⁸

The Court’s reasoning rejects the conventional ‘carbon leakage’ argument that the demand for fossil fuel will remain constant regardless of any changes in the supply chain. The decision stands in sharp contrast to the view held by the Court of Session in Greenpeace Ltd v the Advocate General, where the material effect on climate change of discontinued oil exploitation in the North Sea was seen as ‘difficult to argue’.¹¹⁹ In addition, Milieudefensie demonstrates that private actors’ duties are no longer fully separate from States’ duties: rather, the company’s emissions reductions duties are legally intertwined with the State’s commitment to the Paris Agreement and its temperature thresholds that define the global and each State’s carbon budget (see Chapter 9).

Accordingly, three important insights resonate from the judgment in Milieudefensie and define the Court’s position on attribution. The first concerns the Court’s emphasis on a scientifically supported and internationally endorsed consensus that each company must work towards achieving net zero emissions by 2050.¹²⁰ The second insight relates to the recognition of a direct and linear link between Royal Dutch Shell’s GHG emissions, dangerous levels of global warming, and the imminent environmental damage in the Netherlands.¹²¹ Finally, the Court confirmed the plaintiffs’ argument that all CO₂ emissions attributable to the Shell group had to be reduced.¹²² This means that the localised, imminent environmental damage is attributable to the individualised emissions of the Shell group.

17.3.2 Reviewing National Climate Targets and Measures

Cases against governments often concern insufficient national climate targets for mitigation, but lawsuits challenging States’ adaptation measures are also rising.¹²³ Furthermore, and as deadlines for sectoral climate targets approach, new administrative case law begins to emerge that is concerned with adequate response measures if targets are not met.¹²⁴ So far, cases against governments have often relied on a general causal link between the challenged national climate targets, further climate change in the absence of enhanced targets, and an interference with fundamental rights.¹²⁵ The focus rests on whether or not the impugned action or inaction is capable of depriving individual rights,¹²⁶ with the aim of compelling governments to increase ambition levels.¹²⁷ These decisions are covered in more detail in Chapters 7, 9, and 16. The following only draws on some of the relevant case law where climate targets were challenged to point out where the reasoning could also inform the analysis on attribution.

The premise for the review of national climate measures is that the Paris Agreement’s long-term temperature goal can be translated into corresponding global and national carbon budgets and modelled pathways, as in Milieudefensie.¹²⁸ Climate targets and corresponding measures can then be reviewed in light of domestic administrative and constitutional frameworks.¹²⁹ The scrutiny of national targets is most effective in cases where national climate targets are enshrined in law, as seen in Urgenda¹³⁰ and Thomson,¹³¹ and where domestic law includes interim and sectoral targets as in Neubauer¹³² and Deutsche Umwelthilfe.¹³³ Acknowledging the causal link between targets, corresponding national emissions, and their effect on the global carbon budget has indeed been critical for the intervention of courts that in turn increased the level of ambition of the defendant State. These decisions indirectly acknowledge that governments’ targets and corresponding implementing policies constitute factors to which further climate change and related impacts can be attributed. This nexus is reflected in Friends of the Earth Ltd and others v Secretary of State for Business Energy and Industrial Strategy, where the High Court of England and Wales overturned a decision of the Secretary of State as it failed to address how the shortfall towards the national target would be addressed under statutory requirements, and for failure to provide a quantitative explanation to Parliament as required by law.¹³⁴

Courts have an important function when adjudicating on matters such as the role of the Paris Agreement and its implications for national decision-making processes.¹³⁵ For example, the Court of Appeal of England and Wales concluded in R. (on the application of Plan B Earth Ltd.) v Secretary of State for Transport that the Secretary of State had wrongly omitted climate change considerations and due regard for the Paris Agreement in his decision-making on the expansion of Heathrow Airport.¹³⁶ The decision was overturned on appeal, with the UK Supreme Court remarking that ‘the Paris Agreement itself is not Government Policy’.¹³⁷

A similar pattern emerges in other jurisdictions, where the lower courts afford the Paris Agreement and nationally determined contributions (NDCs) a legal valence that is not confirmed in next instance. For example, the Municipal Court in Klimatická žaloba v Government of the Czech Republic decided that the government was legally bound under Article 4(2) of the Paris Agreement, and also under the State’s NDC, to adopt mitigation measures aimed at achieving the objective of its NDCs.¹³⁸ The Court acknowledged a direct link between the State’s climate target, the adequacy of measures, and the impact on the global climate.¹³⁹ Moreover, the Court applied the rules on treaty interpretation enshrined in Article 31, paragraphs 1 and 2(a), of the Vienna Convention on the Law of Treaties,¹⁴⁰ which are recognised as customary international law.¹⁴¹ However, on 20 February 2023, the Supreme Administrative Court overturned the decision in Klimatická žaloba v the Government of the Czech Republic, based on the collective nature of the EU Member States obligations to reduce GHG emissions by 55 per cent by 2030, and referred the case back to the Municipal Court.¹⁴²

Arguments concerning ineffective mitigation measures and non-compliance with governments’ own targets were also tested based on private law in two cases brought against the French government in the Paris Administrative Court and the Conseil d’Etat. These cases illustrate that ecological damage can be attributed to emissions that exceed the State’s target.

The Paris Administrative Court applied a specific tort law provision of the French Civil Code¹⁴³ that prescribes that every person is responsible to provide reparation for ecological damage.¹⁴⁴ The Court thereby affirmed that exceeding the national emissions limits will lead to ecological damage; in other words, the damage is attributable to the State’s excess emissions. In a second decision, the Court then decided that the ‘Prime Minister and the competent Ministers are ordered to take all useful measures to repair the ecological damage and prevent it worsening for the share of greenhouse gas emissions not made good compared to the first carbon budget’.¹⁴⁵ In a similar vein, the Conseil d’Etat in Grande-Synthe¹⁴⁶ found that the French government was under an obligation to take additional measures by 31 March 2022 to meet the target of reducing GHG emissions by 40 per cent compared to 1990, by 2030.¹⁴⁷

It should be noted that the argument that an event is attributable to climate change may serve as a defence for the Respondent. In Burgess v Ontario Minister of Natural Resources and Forestry, both parties to the dispute argued that the damage was attributable to climate change.¹⁴⁸ After the flooding in Houston, Texas, caused by Hurricane Harvey,¹⁴⁹ owners of properties upstream of the Addicks and Barker Dams brought suits against the United States. They alleged an uncompensated taking under the Fifth Amendment.¹⁵⁰ The government argued that it was not responsible for the harm that resulted from the flooding because the damage was attributable to Hurricane Harvey as an ‘Act of God’.¹⁵¹ The Court of Federal Claims joined all cases and then split them into two sub-dockets, one for the Upstream cases and one for the Downstream cases.¹⁵² For the Upstream cases, the Court determined that the United States was liable to thirteen property owners under the Fifth Amendment of the United States Constitution for the taking of a non-categorical, permanent flowage easement on their properties.¹⁵³ These easements were the result of government-induced flooding during Hurricane Harvey and produced by the government’s construction, maintenance, and operation of the Addicks and Barker Dams.¹⁵⁴ For the Downstream cases, the Court granted the government’s motion to dismiss and denied appellant motion for summary judgment.¹⁵⁵ On appeal, the United States Court of Appeals for the Federal Circuit remanded the case back to the Court of Federal Claims to consider, inter alia, whether Appellants have established causation when considering the impact of the government actions that address the relevant risk.¹⁵⁶

17.3.3 Permissibility of Emissions-Intensive Projects or Activities

Cases concerning the permissibility of emission-intensive projects and activities regularly involve private actors. Litigation against corporations, especially against so-called ‘carbon majors’,¹⁵⁷ is on the rise and contiguous strategies are constantly refined.¹⁵⁸ Cases are often initiated by non-governmental organisations to halt emissions-intensive infrastructure projects or activities. In some instances, lawsuits have also been initiated by local or State governments: for example, several States have filed suits in the United States, seeking to hold oil and gas companies liable for climate change-related harms.¹⁵⁹ A couple of States have also tried to challenge federal measures such as quantifying estimates for the social costs of GHG emissions.¹⁶⁰

A key case for causation and attribution that is still pending in second instance before the Higher Regional Court in Hamm (Court of Appeal, ‘Oberlandesgericht’) at the time of writing is Lliuya v RWE, as mentioned earlier.¹⁶¹ The case is based on German nuisance law (section 1004 Civil Code) and concerns climate adaptation measures in response to flood risks. The claimant, a Peruvian farmer from the Andes region, requests a pro-rata contribution of the energy company for protection measures against flood outburst of the glacial Lake Palcacocha, thus a contribution to adaptation costs. The claimant’s calculation, which is open for the Court’s own determination, is rooted in the global percentage of historic emissions contributed by RWE, amounting to 0.47 per cent according to a study of carbon-major corporations.¹⁶² In the first instance, the Regional Court in Essen (‘Landgericht’) rejected a causal link between the contributions of RWE to global climate change, due to the many contributions and contributors to climate change.¹⁶³ A mechanistic application of the ‘conditio sine qua non’ (equivalent to ‘but for’) formula prevented the Court from engaging more closely with scientific evidence that seeks to attribute quantifiable amounts of emissions to specific major emitters. By contrast, the Higher Regional Court stated that the case was conclusively argued (meaning the legal argument per se is valid and the case will depend on providing pertinent evidence) and allowed it to proceed to trial. Now at the evidentiary stage, claimants must prove that there is a serious threat of an avalanche that could lead to flooding, and they must demonstrate how this would affect the property of the claimant.¹⁶⁴

Cases to compel further regulatory action or to review authorities’ approval for emissions-intensive infrastructure projects have been brought across jurisdictions. These include situations where authorities below the level of national government unlawfully refused to take regulatory action,¹⁶⁵ limited public participation, and/or insufficiently considered climate change impacts when granting permissions.¹⁶⁶ The latter category impliedly connects emissions attribution (e.g. the anticipated future emissions) and event attribution (the contribution of the project to further climate-related impacts). For example, in Earthlife Johannesburg v Minister of Environmental Affairs, the High Court of South Africa held that an assessment of climate change impacts in the environmental authorisation process will ‘best be accomplished by means of a professionally researched climate change impact report’.¹⁶⁷ This approach was confirmed in Sustaining the Wild Coast NPC v Minister of Mineral Resources.¹⁶⁸ In Save Lamu v National Environmental Management Authority, the National Environment Tribunal of Kenya set aside the EIA licence, because the climate impacts of what would have been the first coal fired power plant in Kenya had not been fully evaluated given that comprehensive access to information had not been possible.¹⁶⁹

The decision in Gloucester Resources Limited v Minister for Planning provides a causal analysis that includes an explicit statement on attribution.¹⁷⁰ The Court stressed the causal link between the proposed coal mine, climate change, and further impacts, stating that: ‘[A]ll of the direct and indirect GHG emissions of the Rocky Hill Coal Project will impact on the environment’.¹⁷¹ The additional emissions would be directly attributable to the project. Consequently, a measurable impact of the project on the environment would be attributable to the project and the emissions generated by it.¹⁷²

In Citizens for a Healthy Community v U.S. Bureau of Land Management, the Court held that the agency had failed to comply with the National Environmental Policy Act by not taking a hard look at the reasonably foreseeable indirect impacts of authorising oil and gas developments.¹⁷³ In Sierra Club v Federal Energy Regulatory Commission, the US Court of Appeal for the District of Columbia Circuit found that the Federal Energy Regulatory Commission should have considered the impacts of the project’s downstream carbon emissions and climate effects, or explained why such considerations were not relevant for the project.¹⁷⁴ All of these decisions strengthen the proposition that, from a legal point of view, measurable climate impacts could be attributed to a concrete project and its respective emissions.

A more direct attempt to attribute quantified emissions amounts to a certain activity was made in the Indonesian case Ministry of Environment and Forestry v PT Asia Palem Lestari, in which the Ministry challenged a private company for the illegal burning of peatland.¹⁷⁵ The government argued that the clearing of peatland for a palm oil plantation released 2,700 tonnes of carbon into the atmosphere and that the activities led to a loss of carbon sinks equal to 945 tonnes of carbon.¹⁷⁶ The District Court of North Jakarta dismissed the case because the Ministry had failed to include other landowners as concerned parties.¹⁷⁷ Meanwhile, the Supreme Court of Indonesia decided in a tort-based lawsuit in Minister of Environment v PT Selatnasik Indokwarsa and PT Simpang Pesak Indokwarsa that a quantifiable amount of emissions was attributable to illegal mining activities and awarded the Indonesian Ministry of Environment restoration costs and compensation for GHG emissions.¹⁷⁸

17.3.4 Expanding the Normative Lens

Instantiations of emerging best practices that could change the analysis of causality often result from re-assessing legal concepts. For example, the Constitutional Court in Neubauer re-conceptualised the meaning of ‘interference’ with a fundamental right and developed the ‘advanced interference like effect’.¹⁷⁹ Other courts draw from precedent outside the climate context to adjust the threshold for review. An example is Hauraki Coromandel Climate Action Inc v Thames-Coromandel District Council.¹⁸⁰ The Court opined that judicial review in the context of climate change deserves ‘heightened scrutiny’, as ‘decisions about climate change by public decision-makers is similar to that for fundamental human rights’.¹⁸¹ A key example in that respect is Mathur v Ontario, where seven young claimants made an application in ‘solidarity with millions of youth in Ontario and around to world’, to the Superior Court of Justice of Ontario (Canada), seeking, inter alia, a declaration that Ontario’s climate target to reduce GHG emissions by 30 per cent below 2005 levels by 2030 violated their rights and that of future generations.¹⁸² They asserted that Ontario had to establish a science-based target consistent with Ontario’s share of the minimum level of GHG reductions to limit global warming to below 1.5°C above pre-industrial temperatures, or, in the alternative, well below 2°C.¹⁸³

The Canadian Court first rejected the government’s motion to dismiss the application,¹⁸⁴ stating that many of the claims were capable of scientific proof,¹⁸⁵ and that the applicants should be afforded the opportunity to present their full evidence.¹⁸⁶ In its decision on admissibility, the Court also elaborated on the standard of proof for causation, based on the jurisprudence of the Supreme Court of Canada on the more flexible ‘sufficient causal connection’ standard.¹⁸⁷

In its decision on the merits, the Superior Court of Ontario made several important statements about causality.¹⁸⁸ First, it held that the government’s target as the impugned action did not need to be the dominant or the only cause for the prejudice suffered by the claimants.¹⁸⁹ The Court explained that ‘while Ontario’s contribution to global warming may be numerically small, it is real, measurable and not speculative’.¹⁹⁰ Second, the Court relied on evidence stemming from event attribution science: it acknowledged that the applications had established on a balance of probabilities that the State action ‘contributes to an increase in the risk of death or in the risks faced by the Applicants with respect to the security of the person’.¹⁹¹ Third, the Court found that by setting a climate target below the ‘scientific consensus’ of what would be required to align with 1.5°C, Ontario was ‘contributing to an increase in the risk of death and in the risks faced by the Applicants and others with respect to the security of the person’.¹⁹² Fourth, the Court acknowledged that the ‘causal connection standard’ was sensitive to the context of the particular case, explaining that a very high causal standard would serve to hinder solving global problems.¹⁹³

The Court thus rejected the government’s argument that to meet the causal connection standard, the applicants had to prove ‘beyond a reasonable doubt’ or ‘even on the balance of probabilities’ that the harm will occur. Nevertheless, the Court dismissed the case given that the rights under section 7 of the Charter had to be interpreted as a restriction on the State’s ability to deprive of the rights and did not (yet) include positive obligations.¹⁹⁴ A further argument concerning intergenerational equity was equally rejected, based on the inability of the Court to determine a generational cohort as an analogous ground under section 15(1) of the Charter.¹⁹⁵ This decision is on appeal at the time of writing.

Courts have of course expressed different views on the possibility to adjust thresholds for judicial review. The Supreme Court of Norway in Greenpeace Nordic found that wherever the Storting (Norwegian Parliament) had considered a matter, the threshold for review must be very high.¹⁹⁶ In a similar vein, the concepts of heightened judicial scrutiny, or variable intensity review, were rejected in Students for Climate Solutions Inc v Minister of Energy and Resources where the Court explained that ‘what varies is the nature and extent of the legal controls over discretions, not the intensity with which the Court undertakes its tasks’.¹⁹⁷

In some cases, courts have turned to legal developments that are external to the growing body of climate law. Scholars have pointed out that in China, cases concerning air pollution begin to serve as a gateway for climate change litigation.¹⁹⁸ Courts have applied the ‘burden shifting’ doctrine under the Chinese Tort Liability Law (TLL) 2009, which operates on a legal presumption of causation and shifts the burden to prove the absence of a causal relation in environmental tort disputes to the defendant.¹⁹⁹

Another approach for assessing causation and attribution stems from the introduction of case categories, as in R (on the application of Richards) v Environment Agency, a case concerning unsafe levels of hydrogen sulphide from a landfill site.²⁰⁰ The case was overturned on appeal.²⁰¹ However, it is interesting to note that the High Court for England and Wales had reasoned that, in some situations, courts should acknowledge a presumed causal chain in line with scientific knowledge, at the point where intervention was still possible and harm could be avoided. Although this case is concerned with air pollution and not climate change directly, it is nevertheless instructive as the Court made several impactful statements about causation and attribution, derived from European Court of Human Rights’ jurisprudence that had also been previously endorsed by the UK Supreme Court.²⁰²

The Court distinguished two main categories, the so-called ‘look back’ and the ‘in the moment’ cases. The Court held that the inexorable logic of these human rights cases, especially the ‘in the moment cases’, is that ‘public authorities – and courts – must “step up” at the time when it is still possible to prevent that the foreseeable damage will materialise’.²⁰³ In other words, in situations where the causal chain has not yet fully materialised, the duty of ‘stepping up’ entails that authorities must act before a damage occurs and despite remaining uncertainties. This approach aligns with the precautionary principle.²⁰⁴

17.4 Replicability

Replicability of any of the approaches and analytical arguments related to climate causality will depend on factual circumstances and several tangible and intangible factors. Tangible factors comprise the similarity between jurisdictions (e.g. common law, civil law) and the often-nuanced approach of domestic legal frameworks towards the applicability of international treaty law (variations of monism/dualism). Intangible factors include how courts engage with scientific evidence, foreign case law, and normative considerations pertaining to case categories and thresholds for establishing causation and attribution. Furthermore, the perception of the urgency of the threat of climate change as a societal challenge, global emergency, and/or national crisis inevitably influences the balancing of interests and frames the decision-making.²⁰⁵ While climate change continues to be viewed globally ‘as the gravest threat to humanity’, there are divergent senses of urgency and country-specific priorities across jurisdictions.²⁰⁶

Engaging with expert evidence is critical to any consideration of climate causality and for the transfer of judicial arguments. Domestic courts using international law generally,²⁰⁷ and the Paris Agreement in particular,²⁰⁸ have already contributed to an inter-jurisdictional judicial discourse on climate change that gradually corroborates judicial reasoning on legal concepts.²⁰⁹ Some courts have shown a tendency to adopt a comparative law approach by referencing other courts to address opposing views of their own executive branches or public authorities, especially when confronted with the task of safeguarding fundamental rights, or in ensuring compliance with administrative rules.²¹⁰

A court that endorses the reasoning on climate causality in its own jurisprudence validates and strengthens a legal position. Applying domestic law to a global challenge can thus unfold a harmonising effect for legal concepts such as causation and attribution. The following pathways exist to replicate any of the structural arguments:

• Engaging with scientific evidence, including attribution studies, and with social sciences research.

• Including all GHG emissions into the scope of judicial scrutiny, whether reviewing national climate targets or emissions-intensive infrastructure projects and activities.

• Clearly distinguishing between general causation, specific causation, and attribution.

• Engaging with the findings of other courts in a comparative legal approach.

• Drawing from normative developments outside the climate change context to ensure coherent approaches in environmental jurisprudence.

17.5 Conclusion

This chapter speaks to the lawyer (or judicial officer) and to the climate scientists in its attempt to explain causation and attribution in law and science, and to systematise the global case law that shapes the normative context for climate causality. Three main points resonate from the analysis. First, the chapter has filled a gap in the literature by defining general causation, specific causation, and attribution as distinct but overlapping components of climate causality, and it has explained the various approaches used by scientists in attribution studies. This instils much needed conceptual clarity in a complex area of law, including the law/science intersection. Second, it has advanced the idea of a global, inter-jurisdictional judicial discourse on climate change, by structuring the case law through four key areas of judicial engagement with climate change (the determination of the scope of relevant emissions, the review of national climate targets and measures, the permissibility of emission intensive projects or activities, and courts’ willingness to use and review general (environmental) law concepts to develop climate litigation). From these four areas, transferable arguments on climate causality already emerge which could tighten the normative context in future cases on attribution. As has been discussed, it is necessary to clearly distinguish between the factual considerations that define general and specific causation, and the normative assessment that furnishes attribution. Legal attribution involves a range of normative considerations that determine ‘adequacy’ in the causal chain. These normative considerations can exclude or include anthropogenic emissions as causal factors.

Third, the chapter provides a foundation for further interdisciplinary research on attribution. The legal concept of attribution is well suited to trace the relevant scientific evidence, and its benefit for litigation will not only depend on science-informed law but also on law-informed scientific research. Crucially, attribution in law seeks to assign the legal responsibility for a concrete impact or damage to a specific human action or omission; it requires a qualification and a quantification of the human contribution. It is not sufficient to scientifically attribute an increased risk or a harm to human-induced climate change without further specifying the contribution of the ‘human factor’. Research on the possible expansion of logical fundamentals of the causal analysis,²¹¹ and the introduction of the ‘distinctive causal field’,²¹² have further elaborated the logical operation that the law could use to trace attribution science.²¹³ So far, emerging best practice on attribution is scarce, and allowing a case to proceed to the evidentiary stage as in Lliuya v RWE is a significant step that signals judicial engagement with this attribution science. The growing body of case law where courts already engage with climate science and social sciences, national and international law, and with the arguments derived from the reasoning of other courts can be described as global climate jurisprudence. This global climate jurisprudence comprises pathways for the replicability of arguments. It may even serve as the basis for emerging normative parameters that carry the fairness discourse on climate change forward, within and beyond climate causality.

18 Remedies

Juan Auz and Marcela Zúñiga ^*

18.1 Introduction

The right to a remedy is based on the idea that whoever commits a wrongful act must repair the damage caused.¹ The standard that reparation is expected to achieve is full restitution, that is, that the affected party is restored to the status quo before harm. In the intricate tapestry of climate litigation, the concept of a legal remedy stands as a pivotal culmination point in the process, offering a beacon of resolution and redress for the parties involved. At its core, a legal remedy represents the means through which the rights of individuals or entities are enforced or the violation of said rights is prevented or redressed.

As climate change impacts intensify globally, the quest for adequate remedies in climate litigation has become paramount, serving as the tangible bridge between abstract legal principles and real-world outcomes. These remedies can be broadly categorised into different types based on their nature and objective.² Reparation is one remedy to restore the injured party to the position they would have been in had the violation not occurred. This might include restitution or the restoration of specific property or rights.³ On the other hand, injunctive relief is forward-looking and aims to prevent further harm or violation.⁴ Like injunctive relief, a writ of mandamus is unique due to its origins as an extraordinary writ or remedy and its distinct legal guidelines. This writ obliges a public official to perform a non-discretionary ministerial duty.⁵ To obtain a writ of mandamus, the petitioner must prove that a governmental agency has breached an unambiguous legal obligation and lacks any other sufficient means to achieve the desired outcome.⁶ These are particularly relevant in climate cases where ongoing activities may contribute to environmental degradation. Compensation, another critical remedy, focuses on providing monetary relief to the injured party for loss and damage.⁷ This becomes especially pertinent in climate litigation cases where environmental damages might have led to economic losses for communities or regions.

One of the most comprehensive and earliest exercises to consolidate the practice of remedies in international law, which to a significant extent reflects the practice at the national level, comes from the International Law Commission (ILC), which documented since the late 1970s State practice relating to the international responsibility of States.⁸ The 2001 final report recognised that reparation could take three forms: restitution, compensation, and satisfaction. In parallel, international human rights law, specifically the work of rapporteur Theo Van Boden,⁹ added rehabilitation and guarantees of non-repetition to the list. Consequently, the right to a remedy implies a wide range of modalities, the determination of which will depend on the specific type of violation, that is, on the primary norm that establishes the content of the obligation transgressed.

This chapter aims to show the status and debates concerning remedies in climate change litigation.¹⁰ To this end, the chapter will describe the general framework of the right to a remedy, briefly explaining its evolution and content. It will then analyse how courts and tribunals have interpreted the right to a remedy. Finally, five examples of emerging best practices will be presented, along with tools that judges can use to replicate reparations in climate change litigation.

18.2 Background to Legal Remedies

The right to a remedy in most national systems is based on the idea that whoever commits a wrongful act should repair the harm caused.¹¹ Remedies are woven into the fabric of various legal systems, each presenting its nuanced approach to redress and relief. In tort law, remedies primarily focus on compensating the aggrieved party for harm due to another’s wrongful act. For instance, under the common law principle, the English tort system emphasises compensatory remedies, often monetary, to place the injured party in a position they would have been without the tortious act.¹² Similarly, in the US, the Restatement (Second) of Torts provides for damages to be awarded for harm resulting from negligence, strict liability, or intentional wrongs.¹³ On the other hand, constitutional remedies offer redress against violations of fundamental rights enshrined in national constitutions. In India, Article 32 of the Constitution provides the right to constitutional remedies, allowing individuals to approach the Supreme Court directly if their fundamental rights are infringed.¹⁴

Diving into administrative law, remedies are typically geared towards ensuring that administrative agencies and bodies operate within their legal bounds and prescribed mandates. In the European Union, for instance, the Treaty on the Functioning of the European Union under Article 263 provides for annulment, enabling parties to challenge the legality of an act of the institutions. Similarly, Australia’s Administrative Decisions (Judicial Review) Act 1977 sets out grounds for reviewing administrative decisions, emphasising grounds like procedural fairness and jurisdictional error. Through these distinct yet interconnected avenues of tort, constitutional, and administrative law, remedies in comparative law manifest as the bedrock of effective justice, safeguarding rights and ensuring accountability across diverse global legal landscapes.

Since the remedies approach varies considerably from jurisdiction to jurisdiction, this section will focus on discussing remedial practice in public international law, chiefly because the essential traits of remedies lie in its consolidated doctrine, especially in international human rights law. Studying crucial remedial features in international law could also contribute to a general understanding and potential application of their logic and architecture at the national level. The essence of remedies, both nationally and internationally, seeks to prevent or repair harm, which, mutatis mutandi, is the final objective of any climate litigation case, irrespective of the jurisdiction and field of law. Therefore, the essential nature of remedies, which is to right a wrong, is an optimal legal notion for comparative purposes and analytical extrapolation, for example, from the international to the national and vice versa.

Public international law expressly includes the principle of full reparation in the Factory at Chorzów judgment of the Permanent Court of Justice in 1928 by establishing: ‘The essential principle enshrined in the actual concept of a wrongful act is that reparation must, to the fullest extent possible, wipe out all the consequences of the unlawful act and re-establish the situation, which in all probability would have existed if the act had not been committed.’¹⁵ Therefore, under public international law, the principle of full reparation constitutes the basic structure of the obligation of reparation.¹⁶ This was recognised in the ‘Draft Articles on Responsibility of States for Internationally Wrongful Acts’ (Draft Articles), elaborated by the ILC.¹⁷ The Draft Articles establish the general framework of the obligation to make reparation; it considers it as a new ‘legal relationship’ (secondary obligation) that arises after the commission of a wrongful act, that is, the breach of a primary duty contained in a source of international law (treaty or international custom). Thus, Article 32.1 provides that ‘the responsible State is obliged to make full reparation for the injury caused by the internationally wrongful act’. The international obligation to make reparation is also customary law. Thus, it can be invoked even without the ratification of a treaty expressly containing it.¹⁸

For the ILC, and in line with the Factory at Chorzów case, the objective of full reparation is to eliminate all the consequences of the wrongful act and to re-establish the situation that, in all probability, would have existed if the act had not been committed.¹⁹ The result expected after acting against a State for the breach of an international obligation is the substantive aspect of reparation.²⁰ According to the Draft Articles, integral reparation may consist of three measures, which may be applied individually or jointly: restitution, compensation, and satisfaction. Adopting the measure will depend on the damage caused, which may be both pecuniary and non-pecuniary. Consequently, the Draft Articles make the principle of full reparation applicable to non-pecuniary damage.

Restitution consists of the restoration as far as possible of the situation before the commission of the international wrong.²¹ It may take the form of a material return (territory, person, or property) or the revocation of a legal act (for example, the amendment of a constitutional provision, the revision of an administrative act, or the requirement to adopt a rule).²² However, it admits exceptions: it must not be materially impossible and must not entail a burden wholly disproportionate to the cost that the responsible State would incur.²³

Restitution is often inadequate, or insufficient to guarantee full reparation. Therefore, compensation emerges as a second form of redress for the harm caused. Its function is to fill possible gaps to achieve full reparation and to compensate for damage susceptible to financial assessment. As a rule, it is granted by a sum of money.²⁴

Finally, satisfaction is the distinctive form of reparation granted to the extent that the damage cannot be remedied by restitution or compensation. It is often symbolic, reflecting the need for mechanisms in cases where the damage is of such magnitude that it must involve other actions. However, the measure adopted must not be disproportionate to the injury and must not be humiliating for the responsible State.²⁵

Both the principle of integral reparation and the categories established in the Draft Articles have been incorporated in the jurisprudence of the international human rights courts as lex specialis in reparation.²⁶ The lex specialis character is supported by Article 33 of the Draft Articles, which recognises that the obligation of reparation may arise between States and may also be invoked by a person or entity other than a State.²⁷ Therefore, the primary rule determines how and to what extent individuals are entitled to activate international jurisdiction to obtain reparation from the State.

The extent to which the principle of integral reparation can or should be incorporated into international human rights law is debatable. The critical point of the debate revolves around cases in which restitution to the previous situation is unfeasible. In this regard, criticism points to the principle of integral reparation as a ‘double-edged sword’ since the promise of a comprehensive remedy under international standards can never be fulfilled, no matter how inclusive the justice or administrative reparation process may be.²⁸ Roht-Arriaza calls this the ‘basic paradox at the heart of reparation’, the trade-off between restoration to the status quo ante and recognition that such status could not be implemented.²⁹ However, the Inter-American Court of Human Rights (IACtHR) has established that the principle of integral reparation is intended to guide the Court’s decisions to identify a measure of reparation that can come as close as possible to that ideal.³⁰ Therefore, in those cases where restitution is impossible, the consequences of the damage caused must be repaired through measures recognised by law.

The reparation measures set out in the Draft Articles have been adapted to the context and the type of human rights violations heard and resolved by the competent court. The process has included other measures such as rehabilitation, investigation, and punishment of those responsible and guarantees of non-repetition. Although this last category is considered another secondary obligation for the Draft Articles, the IACtHR³¹ and United Nations Basic Principles and Guidelines on the Right to a Remedy and Reparation for Victims of Gross Violations of International Human Rights Law and Serious Violations of IHL (‘Basic Principles’)³² have recognised it as a form of reparation.

In wrapping up this section, the international legal sources previously cited epitomise the quintessential principle that any breach of an obligation necessitates reparation in an appropriate form. It echoes a time-honoured doctrine mirrored in national litigation globally, where reparation serves as the cornerstone for addressing wrongs and ensuring justice. This principle’s resonance across international and domestic terrains underscores the universal commitment to rectify, restore, and renew the legal and moral balance disrupted by breaches, further highlighting the indelible role of reparations in the quest for justice. The application or transplantation of these assumptions to climate change raises fundamental challenges given the particularities of the type of damage, the actors involved, and the diversity of victims: Does the law adopt the categories sufficient to obtain a remedy for climate change? How do we interpret the remedies of public international law in line with the principles of climate change? What concrete actions should States and the international community take to guarantee the right to a remedy for climate change? Legal arguments, plaintiffs, defendants, petitions, and judgments vary significantly from case to case, as shown in the remainder of this chapter. However, what they all have in common is their remedial demands: plaintiffs ask courts to require mainly States, but increasingly also corporate actors, to create or strengthen policies/laws aimed at protecting the climate – via combating deforestation, for instance – or to suspend or reform projects that might harm the climate system.³³

18.3 State of Affairs

For this chapter, remedies or climate remedies are defined as outcomes in climate cases that favour the party seeking a climate-aligned objective, including measures to mitigate, adapt to, and compensate for climate-related impacts.³⁴ According to the latest report on global trends in climate litigation (2023) of the Grantham Research Institute, ‘around 55% of the 549 cases in which either an interim or final decision has so far been rendered have had outcomes that are favourable to climate action’.³⁵ Arguably, the approximately 300 climate litigation cases that have resulted in climate-positive decisions could be deemed cases that have generated climate remedies. Climate remedies take many legal forms, ranging from injunctive relief to writ of mandamus, quashing of administrative permits, and compensation awards.³⁶ These remedies aim to establish non-repetition, prevent further harm, and repair the damage incurred vis-à-vis whole-of-government climate policies, corporate behaviour, and identified polluting projects.³⁷ Courts and tribunals have interpreted remedies in climate litigation quite plurally depending on a manifold of factors, including the remedial aspirations of applicants, the jurisdiction of the court, the court’s approach and mandate to reparations, and the field of law.³⁸

The Netherlands is where two of the most highly cited and studied climate litigation cases have occurred.³⁹ Both of these cases have resulted in climate remedies. The first case is Urgenda Foundation v State of the Netherlands, in which the plaintiffs contested the government’s insufficient efforts to address climate change. Specifically, they criticised the Dutch government for lacking ambition in its domestic climate change strategy, which aimed to decrease greenhouse gas (GHG) emissions by 17 per cent. The plaintiffs achieved a favourable outcome: The Court ruled that the government’s failure to achieve a minimum 25 per cent reduction in greenhouse gas emissions by the end of 2020 would breach Articles 2 and 8 of the European Convention on Human Rights (ECHR) and Article 21 of the Dutch Constitution.⁴⁰ As a result, the Court ordered the State to achieve more significant emissions reductions, thus exemplifying a climate remedy of guarantee of non-repetition and cessation through injunctive relief. A noteworthy aspect of the judgment that delineates the scope of the remedy is the Supreme Court’s assertion that if ‘the government is obliged to do something, it may be ordered to do so by the courts, as anyone may be, at the request of the entitled party’.⁴¹ Although the Court averred that this power to obligate the government to ‘do something’ is a fundamental rule of constitutional democracy, the judicial remedial obligation in this case did not include an order to take specific legislative measures. As such, the State could choose the measures to comply with the judgment.⁴² Following Urgenda, other Urgenda-style cases emerged in Belgium,⁴³ France,⁴⁴ Canada,⁴⁵ the Czech Republic,⁴⁶ Germany,⁴⁷ Poland,⁴⁸ Ireland,⁴⁹ Italy,⁵⁰ South Korea,⁵¹ the United Kingdom,⁵² and the US.⁵³

The other well-known Dutch climate case is Milieudefensie et al v Royal Dutch Shell, in which the plaintiffs contended that Shell’s role in causing climate change constituted a breach of their responsibility according to Dutch law and obligations related to human rights.⁵⁴ They pursued an order from the Court that would require Shell to lower its CO₂ emissions by 45 per cent by 2030, relative to the levels seen in 2010. Furthermore, the claimants sought a complete elimination of emissions by the year 2050, aligning with the objectives of the Paris Agreement. The plaintiffs, although successful, did not get the precise remedy sought. As a matter of remedial award, the Court ordered Shell, directly and via its subsidiaries, to limit or cause to be limited the emissions related to its group’s activities (scope 1 emissions), its business relationships (scope 2 emissions), and the sold products (scope 3 emissions) by at least 45 per cent at the end of 2030, relative to 2019 levels.⁵⁵ This overarching remedy is likely the most ambitious in corporate climate litigation because it entails fundamentally rethinking the energy corporation and its place in producing and potentially diminishing the climate crisis.⁵⁶ A similar case filed in France is worth mentioning. The plaintiff, the French NGO Notre Affaire à Tous, sought (unsuccessfully due to inadmissibility) to order the French oil major Total to undertake action to reduce the CO₂ emissions attached to its operations.⁵⁷ These legal actions pursue climate remedies that can guarantee non-repetition and cessation through injunctive relief.

Examples of Urgenda-like remedies, that is, judicial awards that tackle systemic issues that fundamentally influence GHG emissions, also exist in the Global South. One of the most well-known cases is Future Generations v Ministry of the Environment and Others (Demanda Generaciones Futuras v Minambiente), where twenty-five young claimants from different parts of Colombia lodged a tutela (constitutional injunction) before the Supreme Court demanding human rights protection from climate change exacerbated by the Amazon’s deforestation.⁵⁸ In April 2018, the Supreme Court favoured the plaintiffs and ordered the State to comply with a comprehensive remedy list that involves creating and implementing inter-institutional conservation policies. The Court ordered the President of Colombia and relevant ministerial agencies to liaise with the plaintiffs, affected communities, and interested populations to formulate an anti-deforestation action plan. It also ordered the construction of an ‘Intergenerational Pact for the Life of the Colombian Amazon’ to reduce deforestation and GHG emissions with multi-level implementation strategies.

Climate remedies designed to address economy-wide or structural frameworks are emerging in climate litigation. However, it is expected to encounter several remedies targeting a precise policy or project that intensifies climate change. For instance, plaintiffs in the ‘Climate Fund’ case in Brazil alleged that the government’s decision to render the National Fund on Climate Change, which ensures the implementation of mitigation and adaptation action, was unconstitutional. The Federal Supreme Court agreed, finding the federal government breached its obligation to fully allocate the Fund’s resources for 2019. It ordered the State defendant to abstain from omitting its responsibility and prohibiting the resources’ undue retention.⁵⁹ Similarly, in Ecuador, young plaintiffs claimed that gas flaring is unlawful because it is a polluting practice that contributes to climate change and negatively impacts their constitutional rights. A provincial appeals court accepted the plaintiffs’ arguments and ordered the State to eliminate the gas flaring towers in the plaintiffs’ vicinity within eighteen months and to abolish such practice entirely by 2030.⁶⁰

Awarding climate remedies is not only the prerogative of national courts. In the international realm, judicial and quasi-judicial bodies are also starting to delineate remedies in the context of climate change. For now, there is only one case in which an international human rights body has handed down a decision awarding a climate-related remedy. In Billy et al v Australia, eight indigenous authors from the Torres Strait Islands filed a complaint before the UN Human Rights Committee.⁶¹ The authors claimed that Australia had violated their right to life by not taking sufficient climate mitigation and adaptation measures;⁶² their right to enjoy their culture and traditional way of life due to their interdependence with their islands’ ecological balance, which is being compromised by climate change, thus generating displacement and irreparable cultural harm;⁶³ and their right to privacy, family, and home life due to ongoing and prospective forced abandonment of their homes.⁶⁴

Furthermore, the authors asserted that – by failing to adopt adequate climate action – Australia is making the climate inhospitable for future generations, thereby affecting the specific rights of minors as enshrined in Article 24(1) of the International Covenant on Civil and Political Rights.⁶⁵ The UN Human Rights Committee found that Australia was in breach of all of the rights invoked by the authors except for the right to life and the rights of minors. As a result, the Committee ordered Australia to provide adequate compensation, conduct consultations for needs assessments, continue implementing and monitoring adequate measures to secure islanders’ existence and adopt non-repetition measures.⁶⁶ In line with its past practice, the UN Human Rights Committee refrained from specifying the precise amount of compensation or detailing non-repetition measures, thus leaving the State a degree of discretion.⁶⁷ The Committee did, however, remind Australia of its duty under the Optional Protocol to ensure an effective remedy when a violation has occurred and expressed its wishes to receive from the State party, within 180 days, information about the measures taken to give effect to the Committee’s Views.⁶⁸

Finally, it is essential to mention General Comment No 26 of the Committee on the Rights of the Child on children’s rights and the environment, with particular attention to climate change, which includes a section on effective remedies.⁶⁹ To ensure effective remedies, the General Comment recognises that States must include restitution, adequate compensation, satisfaction, rehabilitation, and guarantees of non-repetition, both for the environment and the children concerned, as well as access to medical and psychological assistance. It also indicates that States should consider the vulnerability of children affected by environmental degradation, particularly in the case of irreversible damage that may last a lifetime. To this end, the Committee recommends the creation of innovative forms of reparation, such as intergenerational committees, to develop and implement rapid reparation measures.⁷⁰

The cases described in this section are salient instances of remedial approaches encompassing injunctive relief, project permit denials, and legislative reforms, all within the remit of the courts’ mandates to award them. Some of them already incorporate emerging best practices, namely adopting a remedial design that merges adaptation and compensation orders in one single judgment while compelling the defendant to provide a reasonable level of specificity in the mandated new legal or policy act. In the next section, these emerging best practices will be further detailed and illustrated through other remedies from comparative case law.

18.4 Emerging Best Practice

Emerging best practices in the judicial ambit of awarding climate remedies could be divided into five elements. The overarching principle – which we identify as the first element of emerging best practice, following Principles 10 and 13 of the Rio Declaration – concerns the importance of providing an effective redress and remedy in environmental matters.⁷¹ The second element relates to the issuing of holistic orders. A holistic approach to remedies means that orders can encompass a diverse range of climate-related measures, for instance an order to reduce GHG emissions alongside a mandate to implement adaptation-related policies and design participatory processes for redressing loss and damage. The third element of emerging best practice is holding the State or private actor to at least the minimum standard of care recognised in law and/or science where awarding more holistic or far-reaching remedies is unfeasible. To help identify the standard of care for mitigation measures – and reflecting the fourth element of emerging best practice – courts can use the concept of ‘fair shares’ of a global carbon budget to determine the exact remedial order. This manoeuvre allows judges to use the most updated methodologies to ascertain the defendants’ level of responsibility for their contribution to climate change and designate appropriate redress options. And finally, the fifth element of emerging best practice relates to compliance-based orders. These orders are characterised by specificity and straightforwardness, whereby the remedial order specifies what the defendant must do to provide redress, thereby enabling effective compliance follow-up.

18.4.1 Providing Effective Redress and Remedy

The Rio Declaration on Environment and Development is a conspicuous authoritative source of law in virtually every jurisdiction.⁷² Principle 10 of the Rio Declaration develops the general framework of procedural environmental justice, including access to justice. A core tenet of access to justice is providing effective redress and remedy where an obligation is breached, which is now emerging best practice in comparative climate litigation. Several courts have elaborated on the importance of this principle of emerging best practice.

In Urgenda⁷³ the Dutch Supreme Court acknowledged that ‘decision-making on the reduction of greenhouse gas emissions is a power of the government and parliament’ and that they have a significant degree of discretion in this respect.⁷⁴ Nevertheless, the Supreme Court recognised that the judiciary has a role in determining whether the government has remained within the limits of the law by which it is bound. The Court emphasised that legal protection against the government is a vital aspect of a system governed by the rule of law:

In the Dutch system of government, the decision-making on greenhouse gas emissions belongs to the government and parliament. They have a large degree of discretion to make the political considerations that are necessary in this regard. It is up to the courts to decide whether, in taking their decisions, the government and parliament have remained within the limits of the law by which they are bound. Those limits ensue from the ECHR, among other things. The Dutch Constitution requires the Dutch courts to apply the provisions of this convention, and they must do so in accordance with the ECtHR’s interpretation of these provisions. This mandate to the courts to offer legal protection, even against the government, is an essential component of a democratic state under the rule of law.⁷⁵

As noted earlier, the Supreme Court ordered the government to increase its climate mitigation efforts and achieve a reduction of at least 25 per cent by 2020 compared to 1990 levels.⁷⁶

In Notre Affaire à Tous,⁷⁷ the Administrative Court of Paris recognised the need to afford the government considerable discretion in implementing a court order related to GHG emission targets. Nonetheless, it explicitly stated that this allowance does not preclude the judiciary from mandating the government to implement more robust climate mitigation measures. These measures are intended to prevent exacerbation of climate impacts and align with the legislative targets established by the government. Consequently, the Court mandated the French government to intensify its endeavours to decrease GHG emissions following the legislative framework:

In the circumstances of this case, it is appropriate to order the Prime Minister and the competent ministers to take all the necessary sectoral measures to compensate for the damage up to the uncompensated share of greenhouse gas emissions under the first carbon budget […]. it is appropriate, as has been said, to order the enactment of such measures within a sufficiently short period of time in order to prevent any worsening of that damage. In the context of the present case, the specific measures to make reparation for the damage may take various forms and consequently express choices which are within the Government’s discretion.⁷⁸

Similarly, in Neubauer,⁷⁹ the German Constitutional Court highlighted that:

It is not, in principle, for the courts to translate the open wording of Art 20a GG into quantifiable global warming limits and corresponding emission amounts or reduction targets. At the same time, however, Art 20a GG may not be drained of substance as an obligation to take climate action. In this respect too, it remains for the Federal Constitutional Court to review whether the boundaries of Art 20a GG are respected ([…]). There is nothing to indicate that Art 20a GG – as a singular exception among the provisions of the Basic Law – is beyond the scope of judicial review with regard to how its regulatory content is Interpreted and applied.⁸⁰

Additionally, the Court emphasised the significance of upholding constitutional boundaries within environmental protection, specifically in the context of climate action. The Court asserted that judicial examination enables consideration of long-term interests, particularly those of future generations, safeguarding them from short-term interests influenced by election cycles:

The Constitution sets limits here on the leeway enjoyed in the political decision-making process to determine whether environmental protection measures should be taken or not. In Art 20a GG, environmental protection is elevated to a matter of constitutional significance because the democratic political process is organised along more short-term lines based on election cycles, placing it at a structural risk of being less responsive to tackling the ecological issues that need to be pursued over the long term. It is also because future generations ‒ those who will be most affected ‒ naturally have no voice of their own in shaping the current political agenda. In view of these institutional conditions, Art 20a GG imposes substantive constraints on democratic decision-making ([…]). This binding of the political process as envisaged by Art 20a GG would be in danger of being lost if the material content of Art 20a GG were fully determined by the day-to-day political process with its more short-term approach and its orientation towards directly expressible interests.⁸¹

Finally, in the landmark ruling of Held v Montana,⁸² a trial court decided in favour of sixteen youth plaintiffs, declaring that a provision in the Montana Environmental Policy Act (MEPA) – which barred the consideration of greenhouse gas emissions and related climate impacts in environmental assessments – unconstitutional.⁸³ Following a seven-day trial, the Court acknowledged that climate change significantly threatened public health. The plaintiffs showcased various damages they suffered due to the state’s neglect of environmental concerns. The court confirmed that the plaintiffs were entitled to a ‘clean and healthful environment’, encompassing climate. It emphasised that Montana’s activities in the fossil fuel sector contributed substantially to global warming, seriously harming the state’s youth. As a remedy, the Court declared its judgment would influence the State’s conduct by invalidating statutes prohibiting analysis and remedies based on GHG emissions and climate impacts.⁸⁴ By refusing to analyse GHG emissions and their corresponding impacts on the climate or being consistent with the Montana Constitution, the court declared the MEPA unconstitutional and permanently enjoined because it removes the only preventative, equitable relief available to the public.⁸⁵

18.4.2 A Holistic Approach to Remedies

It is emerging best practice that the court adopt a holistic approach to remedies where possible.

An example is the Nepalese case of Shrestha v Office of the Prime Minister et al. On 23 August 2017, Padam Bahadur Shrestha filed a legal action before the Supreme Court of Nepal to compel the government to establish new legislation concerning climate change through a writ of mandamus or other appropriate directive to enact such a law.⁸⁶ The basis of the petition was that the existing Environmental Protection Act of 1997 needed to be revised to address climate change and that the Climate Change Policy 2011 had not been implemented. Consequently, due to climate change, Nepalese people and ecosystems have endured significant adverse impacts. The Court ordered the government, as a form of remedy, to introduce a new climate change law covering several critical areas of climate action. These included strategies to both mitigate and adapt to the impacts of climate change, the promotion of low-carbon technologies and a reduction in the consumption of fossil fuels, and the establishment of scientific and legal tools to offer compensation for individuals affected by pollution and environmental deterioration.⁸⁷ The Court instructed the government to draft and implement the new climate law by issuing a writ of mandamus. This action was deemed essential to uphold Nepal’s commitments as outlined in the Paris Agreement and to fulfil obligations stated in the Constitution.

In Leghari v Pakistan, a law student and farmer from Rahim Yar Khan District in South Punjab, Pakistan, faced water shortages and temperature fluctuations on his family’s 500-acre sugarcane plantation due to climate change.⁸⁸ To prompt action from relevant departments and ministries, he initiated a lawsuit against the Federation of Pakistan for not implementing the 2012 National Climate Change Policy and its Framework. He contended that climate change directly affected Pakistan, necessitating immediate government intervention for adaptation to erratic weather patterns. Leghari claimed that the government’s inaction on climate change violated his constitutional rights, specifically the right to life (Article 9) and the protection of human dignity (Article 14). Following the petition, the Lahore High Court ordered the establishment of a Climate Change Commission to expedite measures combating the effects of climate change in Pakistan. Additionally, the Court specified deadlines for implementing actions ranging from urgent to long-term, maintaining oversight through its continuing mandamus authority to ensure the progression of these efforts. The holistic approach of this remedial order lies in the fact that the High Court of Lahore was tasked with overseeing the implementation of the entirety of the National Climate Change Policy and its Framework for Implementation. Also reflecting best practice was the Court’s follow-up proceedings in 2018 to assess compliance with its initial order, whereby the Court constituted a ‘standing committee’ to create an ongoing link between the Court and the executive.⁸⁹

In the Josefina Huffington Archbold v Colombia case, the plaintiff, a citizen from the islands of Providencia and Santa Catalina in Colombia, filed a constitutional injunction against the State for human rights violations. The case concerned the planning and executing of the action plan to aid the islands following Hurricane Iota in November 2020, which destroyed 98 per cent of the islands’ infrastructure.⁹⁰ The Constitutional Court deemed that the State did not deploy a diligent response plan, which is why it ordered, as a remedy, all the relevant ministries to mobilise resources and personnel to the islands. The Court continued to stress that the respondent State had to implement concrete measures to systematically alleviate the humanitarian emergency and rebuild the infrastructure to adequately provide all essential services guaranteed in the Constitution as fundamental rights. Additionally, the Court ordered the government to implement a participatory plan that considers local culture and languages to rebuild the islands in a way that strengthens resilience to future climate change impacts.⁹¹ In its reasoning for designing this remedy, the Court asserted that the comprehensive reconstruction process must integrate Colombia’s climate adaptation obligations and human rights. The case is, therefore, an illustration of how apex courts are awarding remedies in a holistic fashion, whereby orders of adaptation to climate impacts in extreme weather disasters cannot be deployed without including human rights in a contextualised way.

18.4.3 A Minimum Standard

If the court considers that it cannot issue a holistic remedy – whether because of the way the claim is framed or for other legal or procedural reasons – it is emerging best practice for the court to assess the minimum standard of conduct that the State or private actor must meet to discharge any relevant legal obligations.

A landmark judgment from the Brussels Court of Appeal in Klimaatzaak⁹² exemplifies this. In contrast to the judgment in the first instance (limited to declaratory relief), the Court of Appeal issued an injunctive order requiring the governments to increase their reduction targets to at least 55 per cent of 1990 levels.⁹³ Notably, the Court asserted that utilising its injunctive power against public authorities does not necessarily violate the principle of separation of powers if the judge issues an order consistent with the ‘minimum requirements laid down by norms of international law’ or in the absence of such norms, the ‘minimum requirements’ ‘on the basis of data on which there is scientific and political consensus’.⁹⁴

Regarding the reduction order, the Court noted:

Imposing such a reduction in order to prevent global warming does not, as the Brussels-Capital Region has argued, deprive the public authority of the choice of measures to adopt in order to achieve the objective of limiting global warming, nor does it ‘petrify’ public action, as the Walloon Region maintains (its conclusions on page 84), since it is indisputable (and moreover not seriously contested) that this is an absolutely essential measure (even if not necessarily sufficient) to achieve it, that the Court limits itself to defining a minimum threshold of reduction to be achieved in several years’ time, below which there is fault or negligence (a threshold which the respondents in the main proceedings are therefore free to raise), and that there is a wide range of concrete measures available to these authorities to enable them to achieve this objective (as illustrated by the extensive discussion of measures already taken in the respondents’ submissions in the main proceedings).⁹⁵

The rationale for this judgment is grounded in the violation of human rights (specifically, Articles 2⁹⁶ and 8⁹⁷ of the ECHR) and civil liability principles (Articles 1382 and 1383 of the Civil Code). In its conclusions, the Court of Appeal confirmed that granting an injunction to reduce emissions was the ‘best, if not the only’ way to correct the shortcomings on the part of the State under the ECHR (which contains the right to an effective remedy under Article 13)⁹⁸ and the extracontractual liability provisions of the Civil Code.⁹⁹ It explained:¹⁰⁰

In view of the shortcomings noted in the past and which continue to this day, which can only be corrected by reductions to be planned for the future, in view of the threat posed to the right to life, private life and family life of the appellants, natural persons, by ongoing global warming, in view of the urgency of the measures to be taken during the present decade, in view of the importance of maintaining, at international level, the mutual trust of the States parties to the UNFCCC in the fact that each State will effectively contribute to the global fight against global warming, in view of the absence of any concrete sanction to date for failure to meet the European objectives, it is justified, both in terms of the violation of articles 2 and 8 of the ECHR and of articles 1382 and 1383 of the former Civil Code, to issue an express injunction to the Belgian State, the Brussels-Capital Region and the Flemish Region to take, in consultation with the Walloon Region, the appropriate measures to ensure that Belgium achieves by 2030 the target of a 55% reduction in GHG emissions from its territory compared with 1990.

In so doing, the Brussels Court of Appeal adopted an approach similar to that of the Supreme Court in Urgenda. The Supreme Court, in that case, focused on the ‘absolute minimum’ required by the State to discharge its obligations under the ECHR¹⁰¹ – while leaving it to the government to determine the specific programme, law, or mechanism to reduce GHG emissions by that amount.

18.4.4 Drawing on a Global Carbon Budget

Another element of emerging best practice in climate litigation to date concerns using a global carbon budget to determine the appropriate remedy. This is often linked to determining the ‘minimum standard’ discussed earlier and to the ‘fair shares’ concept.¹⁰²

The most pertinent case in this respect is the famous German constitutional case of Neubauer et al v Germany. This case started with a cohort of young individuals from Germany filing a legal challenge against the Federal Climate Protection Act in the Federal Constitutional Court. They contended that the Act’s objective of decreasing GHG emissions by 55 per cent by 2030 compared to 1990 levels was inadequate.¹⁰³ The plaintiffs claimed that this insufficiency consequently violated their human rights as safeguarded by Germany’s Constitution. The Court ruled in the plaintiffs’ favour. Given the risk of irreversible climate change manifested in the Climate Protection Act, the Constitutional Court based its rationale on the carbon budget estimates of the Intergovernmental Panel on Climate Change (IPCC) to limit warming to 1.75°C. In light of the technical insights from the IPCC and the German Advisory Council on the Environment, the Court ordered the legislature to set clear and specific provisions for reduction targets from 2031 onwards by the end of 2022 based on the size of the remaining global CO₂ budget under the Paris Agreement’s temperature limits of well below 2°C and, if possible, to 1.5°C.¹⁰⁴ This injunctive relief is an example of a remedy designed to avoid overshooting a global carbon budget. The order also demands a significant level of specificity that the legislature must comply with in making the new climate legislation.

The Court based its decision on the principle of proportionality to underscore the need to manage the required emissions reductions for achieving climate neutrality equitably and proactively, ensuring that the curtailment of freedoms remains reasonable despite climate challenges. Specifically, it points out that the protective mandate of Article 20a of the German Basic Law emphasises preserving the natural foundations of life for both present and future generations, advocating for environmental stewardship that avoids imposing radical restraint on future generations.¹⁰⁵ Additionally, it underscores the importance of judiciously consuming the remaining CO₂ budget to buy critical time, enabling necessary transformations that alleviate freedom losses. The Court emphasises the significance of forward-looking legislation that respects fundamental rights.¹⁰⁶

Another illustrative example of this practice of relying on a carbon budget to establish an appropriate remedy is the Gloucester Resources Limited v Minister of Planning in Australia. The mining company Gloucester Resources Limited filed a legal action against the Minister of Planning, contesting the rejection of the company’s proposal to build an open-pit coal mine known as the Rocky Hill Coal Project in New South Wales. This project aimed to extract 21 million tons of coal over sixteen years.¹⁰⁷ The Land and Environment Court of New South Wales upheld the Minister’s denial of Gloucester Resources’ application, finding that the size of the mining project would be a significant source of GHG emissions. Therefore, the project’s refusal could contribute to remaining within the global carbon budget and achieving the long-term temperature goal under the Paris Agreement.¹⁰⁸

The Brussels Court of Appeal in VZW Klimaatzaak v Kingdom of Belgium et al also drew on the carbon budget concept to determine the appropriate remedial order in that case. The Court of Appeal assessed whether – in particular under tort law – it would be appropriate to seek an injunctive relief to prevent ‘damage (so-called dangerous global warming and excessive damage to the residual carbon budget) [that] has not yet occurred’.¹⁰⁹ The Court affirmed that ‘in the current state of positive law, an action to prevent future damage is admissible when the fault has already been committed, and the damage is sufficiently serious’.¹¹⁰ To reach its remedial order, the Court relied upon climate science reports that introduce the notion of carbon budgets to determine what economy-wide GHG emission reduction goals would allow Belgium to contribute to keeping the 1.5°C long-term temperature limit within reach considering a residual global carbon budget of 400 GtCO₂, as noted by the IPCC’s AR6.¹¹¹ On this basis, the Court determined that a reduction of 55 per cent in GHG emissions by 2030 (compared with 1990 levels) was the minimum required to discharge its legal obligations.¹¹²

18.4.5 Compliance-oriented Remedies

The final trend of emerging best practice concerning remedies in climate litigation is the inclusion of orders that provide for a specific and unambiguous behavioural route for the defendant and include follow-up action by the Court to facilitate compliance. This type of remedy clearly articulates why specific laws or policies are unlawful or unconstitutional and what the respondent needs to do to rectify their impacts.

For instance, in the Friends of the Irish Environment v Ireland case, applicants filed an appeal in the Supreme Court, arguing that the Irish government’s approval of the National Mitigation Plan in 2017 violated national climate law, the Constitution, and human rights obligations.¹¹³ The Supreme Court issued a judgment quashing the National Mitigation Plan for falling short of the specificity required to provide transparency and comply with the provisions in domestic climate legislation.¹¹⁴ In its decision, the Court elaborated on what minimum standards a new plan should contain, including a sufficient level of specificity so that anyone could judge whether the plan is realistic and reasonable.¹¹⁵ In the Court’s view, a compliant plan should cover the entire period remaining to 2050 and be sufficiently specific.¹¹⁶

It is also possible to see this emerging best practice in the French decisions in the cases of Grande Synthe (which concerned the State’s compliance with its future emissions reduction targets) and L’Affaire du Siecle (which concerned the government’s failure to comply with its past carbon budgets). In the latter case, the Administrative Court of Paris ordered the government to take immediate and concrete actions to comply with its carbon budgets – ultimately ordering the government to offset the amount that it exceeded its carbon budgets.¹¹⁷

These cases and their resulting remedies constitute emerging best practices because judges use their prerogatives in awarding remedies in a way that tends to catalyse a more efficient outcome for a just decarbonised society when the legal rationale favours the pro-climate claimant. Designing and ordering remedies is highly contingent upon the rationale the judge elaborates on and the mandate a court or tribunal was given by law. However, in some instances, judges have a significant level of leeway to decide the best way to guarantee that the source of harm does not repeatedly manifest, thereby having structural effects. These instances in which judges in different jurisdictions can act convergently towards awarding impactful remedies are determined by certain factors that will be elaborated on in the next section.

18.5 Replicability

This section delves into three specific legal opportunity structures that aim to replicate remedial measures for effective climate action across various legal jurisdictions. Legal opportunity structures refer to the institutional aspects and features of the legal system that can either facilitate or hinder the ability of applicants to leverage the law for change.¹¹⁸ These structures may include the accessibility of courts, the judiciary’s predisposition towards specific claims, and the presence of supportive legal precedents. This section frames and discusses three legal opportunity structures that can be replicable across jurisdictions and have already been used in climate litigation.

Firstly, each court or tribunal operates based on a unique mandate, as defined by the legal framework that established it. This foundation gives structure to the court’s operations and empowers judges with the authority to provide remedies or reparations. This ensures that decisions align with the jurisdiction’s rules and regulations. Secondly, there is the ‘Duty to Cooperate’. Using this principle, judges can, independently or upon a plaintiff’s request, create mechanisms for cooperation between jurisdictions. Such measures can result in wide-ranging remedies, from emission reductions to compensation for damage caused by climate change, even if such damage is outside their direct jurisdiction. Lastly, the universally accepted scientific consensus on climate change, mainly as presented in the IPCC reports, offers a solid foundation for climate-related judgments. By drawing on these reports, courts can ensure the accuracy and relevance of their judgments. These three legal opportunity structures might prompt replicability and thus make it more feasible for judges worldwide to implement the emerging best practices described in the previous section with the added value of contextual sensibility. For example, a remedy in a low-emitting, highly vulnerable country might not look like one in a high-emitting, more climate-resilient one. Additionally, the likelihood of compliance with the remedial order in a judgment should also be factored into its design, and some of these legal opportunities could help address potential non-compliance.

Constitutional and supreme courts globally hold mandates derived from foundational legal texts, granting them the authority to order remedies in varied cases. In Ireland, the power of the Supreme Court to provide remedies emanates from the Constitution of Ireland. Articles 34.3.2° and 34.3.3° of the Irish Constitution entrust the Supreme Court and the High Court with the authority to adjudicate constitutional matters. It could be argued that the Irish Constitution legitimised and premised the mandate that led to the Supreme Court’s judgment in Friends of the Irish Environment v Ireland. Similarly, the Constitution of South Africa, under Chapter 8 on Courts and Administration of Justice, endows its High Courts with a broad mandate to decide a constitutional matter within its power by declaring that any law or conduct that is inconsistent with the Constitution is invalid to the extent of its inconsistency; and ordering a limitation to its retrospective effect. The power granted by the Constitution was invoked in EarthLife Africa Johannesburg v Minister of Environmental Affairs et al.¹¹⁹ India’s Constitution, through Article 32, authorises its Supreme Court to issue writs for enforcing fundamental rights. Through this, the Court devised a ‘continuing mandamus’, assuring consistent judicial monitoring. This approach was utilised in the Vellore Citizens Welfare Forum vs Union of India and Ors case to address industrial pollution.¹²⁰ Embedded in legal frameworks, these mandates underscore the pivotal role of constitutional and supreme courts in addressing rights violations, safeguarding the rule of law, and ensuring justice by ordering appropriate remedies.

Given that the practice of adjudication is moving to regional and international courts and tribunals, the courts’ mandates to award remedies in these instances mirror the phenomenon at the domestic level. The United Nations General Assembly (UNGA) Resolution on ‘Basic Principles and Guidelines on the Right to a Remedy and Reparation for Victims of Gross Violations of International Human Rights Law and Serious Violations of International Humanitarian Law’ sets out the remedies available to international human rights courts and tribunals.¹²¹ These include restitution, compensation, rehabilitation, satisfaction, and guarantees of non-repetition. These forms of remedy are present in the treaties that created these adjudicative bodies. Article 13 of the ECHR guarantees the right to effective redress. Article 41 authorises the European Court of Human Rights (ECtHR) to award and afford just satisfaction to the injured party when domestic legislation allows only partial reparation.¹²²

In the Inter-American Human Rights System, Articles 51 and 63 of the American Convention on Human Rights establish how the Inter-American Commission on Human Rights (IACHR) and the IACtHR shall proceed to grant remedies, respectively. Article 51 states that the IACHR is mandated to transmit a report to the State defendant with pertinent recommendations and a deadline to take remedial measures, after which it shall decide whether they were complied with.¹²³ Article 63(1) recognises that the IACtHR shall grant victims appropriate remedies, including fair compensation.¹²⁴

Similarly, Article 27(1) of the Protocol to the African Charter on Human and Peoples’ Rights Establishing an African Court on Human and Peoples’ Rights states that the Court shall issue specific instructions to correct the violation, including the payment of fair compensation.¹²⁵ Several United Nations human rights treaty bodies, arguably weaker in authority than regional mechanisms,¹²⁶ have jurisdiction to receive individual and inter-State complaints. These are sometimes included in optional clauses within the treaty but are often contained in a separate protocol.¹²⁷ Despite no treaty bodies having explicit legal competence to order compensation or other remedies, they occasionally incorporate calls to give restitution, pay compensation, or afford other remedies through their observations on periodic State reports, in general comments, and their views on communications.¹²⁸ Concretely, the basis between different jurisdictions’ mandate to award similar remedies could support the replicability of the emerging best practice identified earlier. For instance, something that the IACtHR might order in a climate case could be, to a certain extent, replicated by the African Court of Human Rights because both mandates have similar scope regarding remedy measures.

Moving on to the second legal opportunity, discussing the international duty to cooperate as a remedy is noteworthy. For remedies awarded in Global South jurisdictions, it could be essential to put the remedy in the context of global climate change. Since many countries in the Global South might face constraints in complying with a remedy that requires structural whole-of-economy decarbonisation measures, adopting a remedy sensitive to this reality might be appropriate and replicable. The main structural obstacle to compliance by developing countries with a potential climate-related remedy is the lack of expertise and resources – both financial and technical – serving as the primary rationale for an approach that integrates a duty to cooperate. In other words, courts could anticipate a potential non-compliance scenario due to systemic barriers and thus resort to interpretive techniques to design context-specific remedies. More concretely, courts could establish obligations requiring States to do their best to cooperate with other States or multilateral institutions to protect the rights of their citizens from climate-related harm.¹²⁹ Ultimately, the formulation of a remedy that integrates a duty to cooperate internationally indirectly addresses the climate justice question by requiring the defendant State to perform its best when it comes to finding international assistance and cooperation, particularly with those States that pollute the most or with financial institutions that might provide appropriate funding. Article 1(1) and (3) of the United Nations Charter¹³⁰ and Article 2(1) of the International Covenant on Economic, Social and Cultural Rights (ICESCR) offer essential doctrinal direction for replication. The ICESCR, more specifically, lays out the duty of States ‘to take steps … through international assistance and co-operation, especially economic and technical, … with the view to achieving progressively the full realisation of … rights’.¹³¹ In connection with this, the ICESCR’s treaty body specified in its General Comment No 3 that international cooperation is an obligation of all States,¹³² an approach that resonates with Article 4 of the United Nations Framework Convention on Climate Change (UNFCCC) and Article 12 of the Paris Agreement.¹³³

The IACtHR’s 2021 case of Julien Grisonas v Argentina highlights international cooperation for human rights redress, exemplified by the establishment of an inter-State group to investigate Operation Condor violations.¹³⁴ The case involves an Argentine couple’s disappearance during the dictatorship and the transfer of their children to Uruguay and Chile. Though Argentina was deemed responsible, the IACtHR emphasised regional collaboration against impunity based on the collective guarantee mechanism obligating States to cooperate. Similarly, the case of Vélez Loor v Panama (2020–2022) underscored shared responsibility amidst the pandemic’s migration challenges, advocating synergy among States, international bodies, and civil society.¹³⁵ As a corollary, the Guiding Principles on Shared Responsibility (2019) offer a framework for collaborative efforts between States and organisations, including climate change cases.¹³⁶ In Neubauer v Germany, the Constitutional Court emphatically reminded the government that due to the genuinely global dimension of climate change, the State must respond to it through international cooperation.¹³⁷ These precedents and principles underscore the importance of international cooperation in addressing complex and cross-border human rights issues, which could be replicable across jurisdictions and integrated into the remedial award.

The last opportunity for replicability of impactful remedial design is using the IPCC reports. In particular, courts can draw upon the reports’ findings to craft orders that require defendants to undertake specific actions to mitigate GHG emissions. By referring to the reports’ projections and scientific assessments,¹³⁸ courts can establish the necessity of emission reduction measures and their corresponding timelines, as in Klimaatzaak, Neubauer, and Urgenda. This alignment of remedies with authoritative scientific consensus enhances the credibility of such orders and lends legitimacy to the court’s intervention. Moreover, incorporating the IPCC reports in crafting injunctive relief ensures that the remedies are not arbitrary but firmly rooted in expert assessment, reinforcing the acceptability of such orders among various stakeholders. This is also the case for remedies relating to adaptation since the IPCC has also published specific reports on that matter, even with a greater level of granularity from a regional perspective.¹³⁹ Courts can leverage this information to design adaptive measures that address specific risks affected parties face. Furthermore, the scientific assessments provided by the reports can aid courts in determining the causal link between specific actions and the resultant damages. This attribution is crucial in assessing liability and quantifying the losses suffered. By relying on the meticulous analysis of the IPCC, courts can arrive at a more accurate estimation of the damages incurred by affected parties, ensuring that the compensation awarded is commensurate with the harm endured. The scientific underpinning of these compensation orders enhances their legitimacy and promotes consistency and fairness in awarding reparations.

18.6 Conclusion

Throughout legal history, the right to a remedy has been transformed and shaped by national laws, public international law, and evolving concepts of justice. While most States initially defined repair as pecuniary compensation, the scope has broadened under international law to include integral reparation encompassing restitution, compensation, and satisfaction. This principle, rooted in the Factory at Chorzów judgment and codified in the Draft Articles, has been adapted by human rights courts, signifying a lex specialis in reparation but manifesting in domestic reparation orders. The principle of full reparation demands that remedies not only address the harm incurred but also strive to restore the status quo ante, ensuring that the consequences of wrongful acts are comprehensively addressed. The diverse range of remedies – from injunctive relief and compensation to more novel approaches like obligations of conduct – illustrates the legal system’s adaptability in seeking to mitigate the impacts of climate change and prevent further harm.

The confluence of legal principles and climate imperatives marks the evolving landscape of climate remedies. Climate remedies, exemplified by over 300 climate-positive decisions globally, strive to mitigate, adapt, and compensate for climate impacts.

Looking ahead, some emerging practices signal a cautious optimism for the role of climate change litigation in shaping novel global environmental policy approaches regarding loss and damage. For instance, the Administrative Court of Paris in Notre Affaire a Tous v France found that France’s inaction had caused ecological damage and awarded compensation for moral prejudice. Also recently, the Zug Cantonal Court, in the case against Holcim, ruled that the plaintiffs from Indonesia are entitled to legal aid.

Incorporating climate remedies into legal discourse necessitates reconciling traditional principles with the complexities of climate change. While the principle of integral reparation serves as a guiding light, its application faces obstacles in cases of non-compliance. Despite this inherent paradox, courts, such as the IACtHR, advocate for creative measures to approximate comprehensive remedies. This approach underscores the essence of reparation as both symbolic and substantial, thus paving the way for innovative climate remedies.

As courts and jurisdictions grapple with climate remedies, the journey ahead requires reconciling legal doctrines with the urgencies of climate crises. The emerging best practices, rooted in holistic, detailed, and scientifically informed remedies, exemplify the adaptable nature of law. Translating these practices across jurisdictions underscores the role of legal structures, mandates, and global scientific consensus in advancing climate action.

In the words of the Philippines Human Rights Commission immortalised in Greenpeace Southeast Asia and Others,¹⁴⁰ courts should:

embrace their power to influence and inspire government action. […] Thus, without favoring any particular party or going beyond their authority, courts should strive to inform, determine, explain and uphold, through their decisions, the rights and obligations of parties concerning particular climate laws, policies and issues. … courts should clarify the factual and legal bases that were found wanting or insufficient to provide guidance not only to the parties but also to future actions. It should be emphasized that even when courts do not rule in favor of the claimants, they still contribute to meaningful climate response through their elucidation of the law and the rights and obligations of the parties. Judicial contribution to the development of the law and jurisprudence on various climate issues is indispensable to the success of the global climate action.¹⁴¹

In conclusion, the evolution of climate remedies encapsulates the fusion of legal traditions, international obligations, and climate urgency. The journey toward comprehensive climate redress navigates the intricate path of balancing legal principles with transformative climate imperatives. The emerging trends in climate remedies unveil the potential of law as a catalyst for climate action, envisioning a future where reparative justice stands as a cornerstone of climate resilience.

19 Recent Landmark Decisions Advancing Climate Litigation and State Obligations

Margaretha Wewerinke-Singh and Joe Udell ^*

19.1 Introduction

The field of climate litigation is evolving at a breakneck pace, presenting a distinct challenge for a project like this Handbook. While compiling it, we witnessed the emergence of numerous landmark decisions that threatened to outpace our analysis. Thanks to the diligent efforts of our contributors, we managed to integrate many of these developments into the relevant chapters. Still, two groundbreaking decisions were handed down after we had submitted the full manuscript of this book for publication: the Advisory Opinion of the International Tribunal for the Law of the Sea (ITLOS) on climate change and marine protection,¹ delivered on 21 May 2024, and the judgment of the European Court of Human Rights (ECtHR) in Verein KlimaSeniorinnen Schweiz and Others v Switzerland, issued on 9 April 2024.² These decisions mark a significant advancement in global climate jurisprudence, reinforcing and expanding upon many of the themes explored throughout this Handbook.

This chapter aims to analyse these late-breaking developments, situating them within the broader context of climate litigation and exploring their implications for future cases. After contextualising these cases and highlighting their key findings, we will draw connections to relevant analysis identified in other chapters, providing an up-to-date perspective on the rapidly evolving field of climate litigation. This analysis will demonstrate how these decisions both reflect and advance emerging best practice in climate jurisprudence, potentially opening new avenues for legal intervention in the global fight for climate justice. We conclude by considering the implications for key issues in climate litigation, and how these rulings have the potential to drive more ambitious and equitable climate action through legal channels.

19.2 ITLOS Advisory Opinion: Clarifying State Obligations under UNCLOS

On 21 May 2024, ITLOS delivered a unanimous Advisory Opinion in response to questions submitted by the Commission of Small Island States on Climate Change and International Law (COSIS). This Opinion represents a significant development in international law as it pertains to climate change, clarifying States’ obligations under the United Nations Convention on the Law of the Sea (UNCLOS) in relation to climate change.

19.2.1 Background and Context

The Commission, representing some of the world’s most climate-vulnerable nations, posed two legal questions to the Tribunal:

What are the specific obligations of State Parties to the United Nations Convention on the Law of the Sea (‘UNCLOS’), including under Part XII:

1. (a) to prevent, reduce and control pollution of the marine environment in relation to the deleterious effects that result or are likely to result from climate change, including through ocean warming and sea level rise, and ocean acidification, which are caused by anthropogenic greenhouse gas emissions into the atmosphere?

2. (b) to protect and preserve the marine environment in relation to climate change impacts, including ocean warming and sea level rise, and ocean acidification?³

19.2.2 Key Findings

The Tribunal’s Opinion demonstrates a commitment to interpreting UNCLOS dynamically in light of current scientific knowledge. By recognising greenhouse gas (GHG) emissions as a form of marine pollution and setting out a range of specific climate-related obligations of States arising from UNCLOS, ITLOS has confirmed that UNCLOS provides a legal basis for compelling more ambitious and equitable climate action.⁴

The Opinion also illuminates the distinct role UNCLOS plays in the overall international legal framework applicable to climate change, including its relationship with the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement. It emphasises that climate measures taken under UNCLOS should be determined objectively, taking into account the best available science and relevant international rules and standards.

This section highlights the key findings of the Tribunal by topic.

19.2.2.1 Jurisdiction

ITLOS unanimously decided it had jurisdiction to give the Advisory Opinion, affirming its role in interpreting UNCLOS in connection with the climate crisis. This determination, however, was not a foregone conclusion, as there was some initial scholarly speculation that procedural obstacles would be a deterrent.⁵

One concern was whether the COSIS Agreement properly confers advisory jurisdiction to the Tribunal pursuant to Article 21 of the ITLOS Statute and Article 138 of the Rules of ITLOS.⁶ In its analysis, ITLOS first considered Article 21, which dictates that its jurisdiction ‘comprises all disputes and all applications submitted to it in accordance with this Convention and all matters specifically provided for in any other agreement which confers jurisdiction on the Tribunal’.⁷ To that end, the COSIS Agreement explicitly states that it is ‘authorized to request advisory opinions from the International Tribunal for the Law of the Sea (ITLOS) on any legal question within the scope of the 1982 United Nations Convention on the Law of the Sea, consistent with Article 21 of the ITLOS Statute and Article 138 of its Rules’.⁸ The Tribunal accordingly explained that the authorisation enabling the Commission to request advisory opinions ‘confers jurisdiction on the Tribunal’ under Article 21.⁹

The Tribunal then turned to the conditions that needed to be satisfied under Article 138; notably that:

(a) there is an international agreement related to the purposes of the Convention which specifically provides for the submission to the Tribunal of a request for an advisory opinion; (b) the request has been transmitted to the Tribunal by a body authorized by or in accordance with the agreement; and (c) the request submitted to the Tribunal concerns a legal question.¹⁰

After analysing the COSIS Agreement, the request for an Advisory Opinion submission process, and the legal nature of that request, the Tribunal concluded that it had jurisdiction to deliver the Advisory Opinion.¹¹

19.2.2.2 Anthropogenic GHG Emissions as Marine Pollution

In a crucial finding, the Tribunal determined that anthropogenic GHG emissions constitute pollution of the marine environment within the meaning of UNCLOS Article 1(1)(4), which defines marine pollution as the ‘introduction by man, directly or indirectly, of substances’ into the marine environment that is ‘likely to result in such deleterious effects as harm to living resources and marine life, hazards to human health’.¹² The Tribunal’s finding on this point is unambiguous: rather than suggesting that GHG emissions may or could amount to marine pollution, the Tribunal found that they do so: ‘[T]he Tribunal concludes that anthropogenic GHG emissions into the atmosphere constitute pollution of the marine environment within the meaning of article 1, paragraph 1, subparagraph 4, of the Convention.’¹³ This interpretation confirms the broad scope of marine pollution under UNCLOS, with the effect of directly linking climate change to the Convention’s regulatory framework. Part of this framework are the obligations flowing from Articles 192, 193, and 194(1)–(2) of the UNCLOS, which are widely recognised as codified rules of customary international law, such as the duty to protect and preserve the marine environment, the principle of State sovereignty over natural resources, and the ‘no harm’ principle, which prohibits activities within a State’s jurisdiction from causing environmental harm to other States. Additionally, the framework includes provisions like Articles 207, 211, and 212, which impose obligations related to pollution from land-based sources, vessels, and the atmosphere.

The Opinion emphasises the obligation of States to exercise due diligence in fulfilling their obligations, with the standard of care required being ‘stringent’ given the high risks of serious and irreversible harm to the marine environment from GHG emissions.¹⁴ This aligns with the precautionary approach, which the Tribunal considers implicit in the very notion of marine pollution under UNCLOS.¹⁵

19.2.2.3 Specific Obligations of States

The Opinion outlines a range of specific obligations for States under UNCLOS.¹⁶ These include the following:

• – Taking all necessary measures to prevent, reduce, and control marine pollution from anthropogenic GHG emissions (Article 194(1));¹⁷

• – Ensuring that activities under their jurisdiction do not cause harm by pollution to other States and their environment (Article 194(2));¹⁸

• – Adopting laws and regulations to prevent, reduce, and control marine pollution from GHG emissions from various sources (Articles 207, 211, 212);¹⁹

• – Enforcing these laws and regulations (Articles 213, 217, 222);²⁰

• – Cooperating in formulating international rules and standards to address marine pollution from GHG emissions (Article 197);²¹ and

• – Conducting environmental impact assessments for activities that may cause substantial pollution or significant harm to the marine environment through GHG emissions (Article 206).²²

19.2.2.4 Role of the Paris Agreement

The Opinion makes it clear that the UNFCCC, the Kyoto Protocol, and the Paris Agreement in no way preclude the application of other rules of international law, nor do they substitute the content of such other rules. It states: ‘The Tribunal also does not consider that the Paris Agreement modifies or limits the obligation under the Convention. In the Tribunal’s view, the Paris Agreement is not lex specialis to the Convention and thus, in the present context, lex specialis derogat legi generali has no place in the interpretation of the Convention.’²³ The Tribunal’s interpretation positions UNCLOS obligations as directly applicable to climate change issues, rather than serving merely as tools to interpret the Paris Agreement. Instead, ITLOS refers to the Paris Agreement in its interpretation of relevant provisions of UNCLOS, while at the same time recognising the independent legal nature of both instruments.²⁴ This approach firmly establishes that States’ climate change obligations under UNCLOS are in no way substituted or diluted by the existence of climate change treaties.²⁵

19.3 KlimaSeniorinnen v Switzerland: A Breakthrough in European Human Rights Law

The ECtHR Grand Chamber judgment in KlimaSeniorinnen, delivered on 9 April 2024, marks a watershed moment in climate litigation.²⁶ The decision represents the first time that the Court has ruled on the application of the European Convention on Human Rights (ECHR) with respect to climate change.²⁷ Notably, the ECtHR not only recognised that climate change implicates various rights protected under the ECHR, it also identified specific positive obligations for States to protect those rights by combating climate change. Moreover, it clarified its standing criteria for associations engaged in climate protection.

The Court announced the KlimaSeniorinnen judgment on the same day as two other climate change cases: Duarte Agostinho v Portugal and 32 other States,²⁸ and Carême v France.²⁹ Duarte Agostinho, which was brought by six Portuguese youth applicants, was found to be inadmissible because jurisdiction was lacking for all respondents save Portugal; and because the applicants had not first exhausted domestic remedies before national courts in Portugal.³⁰ Carême was inadmissible due to a lack of victim status since the applicant – the former mayor of the Grande-Synthe municipality – no longer lived in the affected region of France, having moved to Brussels.³¹

19.3.1 Case Background

After exhausting domestic remedies, where Swiss courts dismissed their claims primarily on standing grounds, the KlimaSeniorinnen association, representing over 2,000 elderly women and four individual applicants, turned to the ECtHR. They alleged that worsening climate impacts – notably heatwaves – were increasingly affecting their health.³² The applicants claimed that Switzerland’s insufficient action on climate change violated their rights under Articles 2 (right to life) and 8 (right to respect for private and family life) of the ECHR. Moreover, they argued that the dismissal of their case in the domestic courts violated their right to a fair trial (Article 6(1)) and right to an effective remedy (Article 13) under the ECHR.

19.3.2 Key Findings

The Court’s reasoning represents a significant contribution to judicial practice on climate change under the ECHR. In particular, the judgment contains several groundbreaking elements with respect to the role of the Paris Agreement; the positive obligations that States have to address climate change under Article 8 ECHR; the standard of review; Switzerland’s violation of Articles 8 and 6(1) ECHR; State responsibility; the rejection of the ‘drop in the ocean’ argument; and the standing of the KlimaSeniorinnen association. The following section highlights and summarises the key findings with respect to each of these issues.

19.3.2.1 Role of the Paris Agreement

KlimaSeniorinnen – along with relevant parts of the Court’s reasoning in Duarte Agostinho and Carême – unequivocally establishes that human rights law is applicable to climate change.³³ The Court also makes it crystal-clear that neither the UNFCCC nor its subsidiary treaties, the Kyoto Protocol and the Paris Agreement, replace or substitute States’ human rights obligations.³⁴ Rather, the Court points at the imperative of an integrated approach whereby States’ commitments under international climate change law coupled with the best available science serve to create a ‘floor’ for States’ obligations under the ECHR:

In line with the international commitments undertaken by the member States, most notably under the UNFCCC and the Paris Agreement, and the cogent scientific evidence provided, in particular, by the IPCC [Intergovernmental Panel on Climate Change] (see paragraphs 104–120 above), the Contracting States need to put in place the necessary regulations and measures aimed at preventing an increase in GHG concentrations in the Earth’s atmosphere and a rise in global average temperature beyond levels capable of producing serious and irreversible adverse effects on human rights, notably the right to private and family life and home under Article 8 of the Convention.³⁵

19.3.2.2 Positive Obligations

The judgment confirms that the ECHR imposes positive obligations on States to take effective measures to mitigate climate change.³⁶ These obligations flow directly from the causal relationship between climate change and the enjoyment of ECHR rights.³⁷ According to the Court, Article 8 ECHR provides ‘a right for individuals to enjoy effective protection by the State authorities from serious adverse effects on their life, health, well-being and quality of life arising from the harmful effects and risks caused by climate change’.³⁸ Each State’s ‘obligation under Article 8 is to do its part to ensure such protection’ and its ‘primary duty is to adopt, and to effectively apply in practice, regulations and measures capable of mitigating the existing and potentially irreversible, future effects of climate change’.³⁹

The Court then laid out a set of specific standards that it would evaluate in climate cases to determine if domestic authorities ‘have had due regard to the need to’:

1. (a) adopt general measures specifying a target timeline for achieving carbon neutrality and the overall remaining carbon budget for the same time frame, or another equivalent method of quantification of future GHG emissions, in line with the overarching goal for national and/or global climate-change mitigation commitments;

2. (b) set out intermediate GHG emissions reduction targets and pathways (by sector or⁴⁰ other relevant methodologies) that are deemed capable, in principle, of meeting the overall national GHG reduction goals within the relevant time frames undertaken in national policies;

3. (c) provide evidence showing whether they have duly complied, or are in the process of complying, with the relevant GHG reduction targets (see sub-paragraphs (a)(b) above);

4. (d) keep the relevant GHG reduction targets updated with due diligence, and based on the best available evidence; and

5. (e) act in good time and in an appropriate and consistent manner when devising and implementing the relevant legislation and measures.⁴¹

The Court arrived at these obligations by adapting its general principles guiding the interpretation of Article 8 ECHR to the specific context of climate change. In Article 8 environmental disputes prior to KlimaSeniorinnen, the Court’s case law established that States have a duty to, inter alia, put in place an adequate legislative framework that will ‘provide effective protection of human health and life’.⁴² These environmental cases refer to situations where ‘there is a nexus between a source of harm and those affected by the harm’, and the requisite mitigation measures are easily identifiable.⁴³

However, the Court found that the key characteristics of climate change are ‘significantly different’ from the circumstances surrounding other environmental cases, thus complicating the adjudication of such disputes.⁴⁴ These features include the multitude of sources that cause GHG emissions; the fact that carbon dioxide is not toxic per se at ordinary concentration levels; the transboundary nature of emissions; and the complex and unpredictable causal chain of events that eventually results in harm to human life.⁴⁵ The Court accordingly asserted that it must adapt the general parameters of positive obligations under Article 8 to effectively address ‘the special nature of the phenomenon’ of climate change’.⁴⁶ In so doing, it ensured that the ECHR, as a treaty protecting human rights, continues to be interpreted such that it is ‘practical and effective, not theoretical and illusory’.⁴⁷

19.3.2.3 Level of Judicial Scrutiny

A central aspect of the Court’s modification of Article 8 ECHR principles was the level of judicial scrutiny it established for disputes in the climate context. When determining if an Article 8 violation has occurred, the ECtHR noted that it will look at whether the respondent State remained within its margin of appreciation.⁴⁸

In KlimaSeniorinnen, the Court established two different margins of appreciation for States.⁴⁹ To do so, it first established a distinction between (1) States’ commitments to addressing climate change; and (2) the manner in which they carry out their climate actions. While acknowledging that States have a wide margin of appreciation in choosing the means to achieve their climate objectives, the Court explained that States have a reduced margin of appreciation with respect to their climate commitments.⁵⁰ This heightened scrutiny is attributed to the ‘nature and gravity of the threat and the general consensus as to the stakes involved in ensuring the overarching goal of effective climate protection’.⁵¹ The Court thus found that States’ discretion in policy choices is confined by an objective requirement to address climate change ‘in good time, in an appropriate and consistent manner’ and base their approach on the best available scientific evidence.⁵²

19.3.2.4 Violation of Article 8

The Court found a violation of Article 8 ECHR based on an analysis of Switzerland’s climate policies under a reduced margin of appreciation.⁵³ Ultimately, Switzerland’s 2011 CO2 Act, 2022 Climate Act, and lack of a quantified carbon budget fell short of meeting the positive obligations described in the previous section. The ECtHR evaluated Switzerland’s ineffective compliance with its Article 8 obligations as follows:

[T]here were some critical lacunae in the Swiss authorities’ process of putting in place the relevant domestic regulatory framework, including a failure by them to quantify, through a carbon budget or otherwise, national GHG emissions limitations. Furthermore, the Court has noted that, as recognised by the relevant authorities, the State had previously failed to meet its past GHG emission reduction targets. By failing to act in good time and in an appropriate and consistent manner regarding the devising, development and implementation of the relevant legislative and administrative framework, the respondent State exceeded its margin of appreciation and failed to comply with its positive obligations in the present context.⁵⁴

In highlighting Switzerland’s ‘critical lacunae’ in its regulatory framework, the Court clearly established that States must have a national carbon budget (or an equivalent) set in light of the global carbon budget to comply with its relevant duty of care.

19.3.2.5 Violation of Article 6(1)

The ECtHR also found a violation of the right of access to a court under Article 6(1) ECHR, concluding that the Swiss courts had failed to engage seriously with the merits of the applicants’ claims regarding the effective implementation of mitigation measures under existing domestic law.⁵⁵ The Court was ‘not persuaded’ by the Swiss courts’ assertion that there was still time to address the most severe climate impacts because the existing scientific evidence ‘suggest[ed] that there was a pressing need to ensure the legal protection of human rights’.⁵⁶ This shortcoming was made clearer by the fact that, according to the ECtHR, domestic courts have a ‘key role’ to play in ensuring effective protection of Convention rights in the climate context, signalling that restrictions on access to justice in environmental matters will be subject to close scrutiny.⁵⁷ Accordingly, Switzerland’s domestic courts did not take the proper action to ensure that the human rights enshrined in the ECHR were being observed.⁵⁸

19.3.2.6 State Responsibility

The KlimaSeniorinnen judgment expressly recognises the application of the general law of State responsibility to climate change to anthropogenic emissions of greenhouse gases from a State. The ECtHR noted that:

[W]hile climate change is undoubtedly a global phenomenon which should be addressed at the global level by the community of States, the global climate regime established under the UNFCCC rests on the principle of common but differentiated responsibilities and respective capabilities [CBRD-RC] of States (Article 3 § 1). This principle has been reaffirmed in the Paris Agreement (Article 2 § 2) and endorsed in the Glasgow Climate Pact (cited above, paragraph 18) as well as in the Sharm el-Sheikh Implementation Plan (cited above, paragraph 12). It follows, therefore, that each State has its own share of responsibilities to take measures to tackle climate change and that the taking of those measures is determined by the State’s own capabilities rather than by any specific action (or omission) of any other State (see Duarte Agostinho and Others, cited above, §§ 202–03). The Court considers that a respondent State should not evade its responsibility by pointing to the responsibility of other States, whether Contracting Parties to the Convention or not […]

This position is consistent with the Court’s approach in cases involving a concurrent responsibility of States for alleged breaches of Convention rights, where each State can be held accountable for its share of the responsibility for the breach in question (see, albeit in other contexts, M.S.S. v Belgium and Greece, cited above, §§ 264 and 367, and Razvozzhayev v Russia and Ukraine and Udaltsov v Russia, nos. 75734/12 and 2 others, §§ 160–61 and 179–81, 19 November 2019). It is also consistent with the principles of international law relating to the plurality of responsible States, according to which the responsibility of each State is determined individually, on the basis of its own conduct and by reference to its own international obligations (see International Law Commission, Draft Articles on Responsibility of States for Internationally Wrongful Acts, with commentaries, Commentary on Article 47, paragraphs 6 and 8). Similarly, the alleged infringement of rights under the Convention through harm arising from GHG emissions globally and the acts and omissions on the part of multiple States in combating the adverse effects of climate change may engage the responsibility of each Contracting Party.⁵⁹

19.3.2.7 Standing

While denying standing to the individual applicants due to actio popularis concerns, the Court granted standing to the KlimaSeniorinnen association, significantly lowering the threshold for associational standing in climate cases.⁶⁰ This decision marks a notable development in the ECtHR’s standing jurisprudence as associations are generally ‘not in a position to rely on health considerations to allege a violation of Article 8’.⁶¹

However, the Court explained that associations have an important role to play in modern societies faced with challenges like climate change, which require complex administrative decision-making processes. In this context, ‘recourse to collective bodies such as associations is one of the accessible means, sometimes the only means, available to [citizens] whereby they can defend their particular interests effectively’.⁶² As such, the Court revealed a broadened standing test for Article 8 climate disputes, which requires that an association is:

1. (a) lawfully established in the jurisdiction concerned or have standing to act there;

2. (b) able to demonstrate that it pursues a dedicated purpose in accordance with its statutory objectives in the defence of the human rights of its members or other affected individuals within the jurisdiction concerned, whether limited to or including collective action for the protection of those rights against the threats arising from climate change; and

3. (c) able to demonstrate that it can be regarded as genuinely qualified and representative to act on behalf of members or other affected individuals within the jurisdiction who are subject to specific threats or adverse effects of climate change on their lives, health or well-being as protected under the Convention.⁶³

Furthermore, when analysing these criteria, the ECtHR stated that it would look to the following factors: the purpose of the association; whether it is of a non-profit character; the nature and extent of its activities; its membership and representativeness; its principles and transparency of governance; and whether granting standing to the organisation would be in the interest of the proper administration of justice.⁶⁴ With respect to KlimaSeniorinnen’s standing, the Court recognised that, as a result of its membership basis, representativeness, and purpose, the association ‘represents a vehicle of collective recourse aimed at defending the rights and interests of individuals against the threats of climate change in the respondent State’.⁶⁵

19.4 Distilling Emerging Best Practice from the Two Decisions

The ITLOS Advisory Opinion and the KlimaSeniorinnen judgment, while emerging from different legal regimes, display notable similarities in their approach to climate change. Together, they contribute significantly to the consolidation of key aspects of the emerging best practices examined throughout this Handbook. This section will identify and connect notable examples of those approaches with the discussions in previous chapters.

19.4.1 Recognition of Urgency

Both decisions acknowledge the pressing nature of climate change and the need for immediate and effective action. This approach represents emerging best practice, reflecting the critical state of the climate crisis as described in Chapters 2 and 3.

For instance, the ITLOS Advisory Opinion relies on IPCC findings to explain that climate impacts due to past and future emissions are ‘irreversible for centuries to millennia, especially changes in the ocean, ice sheets and global sea level’.⁶⁶ The Tribunal also stressed that ‘climate change represents an existential threat and raises human rights concerns’.⁶⁷ Establishing this sense of urgency sets the stage for the novel duties for States outlined later in the decision.

Likewise, KlimaSeniorinnen details and explicitly refers to both the ‘climate emergency’⁶⁸ and the ‘climate crisis’.⁶⁹ Resolving this crisis, according to the Court, demands a ‘comprehensive and complex set of transformative policies involving legislative, regulatory, fiscal, financial and administrative measures as well as both public and private investment’,⁷⁰ with ‘critical issues aris[ing] from failures to act, or inadequate action’ at the State level.⁷¹

These judicial approaches – coupled particularly with the positive climate obligations that States have under UNCLOS and the ECHR – advance emerging best practice in that both decisions properly identify the alarming state of the climate crisis, then explain how States have a legal duty to address this critical situation.

19.4.2 Reliance on the Best Available Science

The ITLOS Advisory Opinion and KlimaSeniorinnen both rely on the best available scientific evidence, particularly reports from the IPCC. In so doing, ITLOS and the ECtHR further emerging best practice by grounding the facts of their respective cases in the most recent scientific consensus on climate change. This reliance on scientific consensus and best available evidence reinforces the importance of robust climate science in litigation, as explored in Chapters 2 and 3, and further identified as emerging best practice throughout the Handbook.

The ITLOS Advisory Opinion maintains that best available science plays a ‘crucial role’ in determining the content of the necessary measures that States must take to prevent, reduce, and control marine pollution.⁷² These findings, according to the Tribunal, are ‘key to understanding the causes, effects and dynamics of such pollution and thus to providing the effective response’.⁷³ Moreover, as due diligence is a variable concept, States must be aware of new scientific developments as they formulate their climate actions.⁷⁴

The Tribunal’s finding that anthropogenic GHG emissions amount to marine pollution was explicitly informed by this best available science. Amongst other things, ITLOS noted: ‘Being itself a component of climate change, ocean warming, according to the IPCC findings made with high confidence, “accounted for 91% of the heating in the climate system” (WGI 2021 Report, p. 11).’⁷⁵ The Tribunal also relied on IPCC reports to establish the content of States’ obligations to address climate change under UNCLOS. In doing so, it made clear that 1.5°C – as opposed to well below 2°C – is the relevant temperature goal of the Paris Agreement:

Such measures [to prevent, reduce and control marine pollution] should be determined objectively, taking into account, inter alia, the best available science and relevant international rules and standards contained in climate change treaties such as the UNFCCC and the Paris Agreement, in particular the global temperature goal of limiting the temperature increase to 1.5°C above pre-industrial levels and the timeline for emission pathways to achieve that goal.⁷⁶

Importantly, ITLOS stressed that the need for alignment with the 1.5°C temperature goal ‘applies equally’ to the obligations to take necessary measures to prevent transboundary GHG pollution under Article 194, paragraph 2.⁷⁷

KlimaSeniorinnen similarly dictates that States align their GHG reduction targets with the best available evidence and update these targets as insights evolve.⁷⁸ To that end, the ECtHR highlighted IPCC reports such as the Special Report on Global Warming of 1.5°C, as well as the Sixth Assessment Report.⁷⁹ The Court expressly added that those reports were not ‘challenged or called into doubt by the respondent or intervening States’.⁸⁰ The findings of the IPCC thereby proved to be essential in terms of establishing the undisputed facts of the case – all of which underscore the magnitude of the current state of the climate crisis:

[T]hat there are sufficiently reliable indications that anthropogenic climate change exists, that it poses a serious current and future threat to the enjoyment of human rights guaranteed under the Convention, that States are aware of it and capable of taking measures to effectively address it, that the relevant risks are projected to be lower if the rise in temperature is limited to 1.5°C above pre-industrial levels and if action is taken urgently, and that current global mitigation efforts are not sufficient to meet the latter target.⁸¹

The Court’s approach here not only further cements the key role of best available science in climate litigation, it also illustrates how that evidence can effectively establish the reference point – specifically the Paris Agreement’s temperature limit of 1.5°C, as opposed to 2°C – that climate action is measured against.

19.4.3 Standing

The ECtHR’s flexible approach to this issue opens new possibilities for collective action in climate litigation. Despite the Court’s more restrictive stance for individuals, its willingness to adapt and broaden its standing criteria for associations in the context of climate change embodies the emerging best practice emphasised in Chapter 5, which highlighted the importance of easing standing burdens in climate litigation.⁸² Accordingly, associations engaged in climate change issues will likely be empowered to represent their membership on rights-based grounds in domestic courts. As the ECtHR’s standing rules are different from those of domestic courts, should domestic courts not find KlimaSeniorinnen’s jurisprudence to be persuasive, associations denied standing at the national level will conceivably have a promising chance for the ECtHR to hear their claims on the merits.

19.4.4 Admissibility

ITLOS and the ECtHR promoted the emerging best practice identified in Chapter 5 by exercising their legal powers to oversee the respective proceedings in a manner consistent with the climate crisis. ITLOS, for instance, invoked its discretion to render its Advisory Opinion by stressing that climate change ‘is recognized internationally as a common concern of humankind’ while also noting ‘the deleterious effects climate change has on the marine environment and the devastating consequences it has and will continue to have on small island States, considered to be among the most vulnerable’.⁸³ Likewise, the ECtHR notably fast-tracked KlimaSeniorinnen, along with Duarte Agostinho and Carême, to the Grand Chamber, thus furthering the notion that climate change requires admissibility to be assessed in a timely manner. The Court’s willingness to admit climate claims brought forward by associations also represents a transparent effort to balance actio popularis concerns with the effective protection of human rights under the ECHR.

19.4.5 Separation of Powers

Both decisions assert a robust role for the judiciary in addressing climate change, while respecting the principle of separation of powers. The ECtHR, in particular, advanced the emerging best practice discussed in Chapter 6 by encouraging more assertive judicial engagement with climate issues at the national and regional levels. On one hand, the Court emphasised the ‘key role which domestic courts have played and will play in climate-change litigation’.⁸⁴ This sentiment will be critical in the near future as domestic courts will most assuredly receive submissions from plaintiffs seeking to hold States accountable for their positive Article 8 obligations. With respect to exercising its own judicial authority, the Court importantly stressed that, despite the deference it extends to the policy-setting authority of States, scrutinising potential ECHR violations falls well within its authority as a matter of law.⁸⁵

19.4.6 Human Rights

Although these rulings both acknowledge the connection between climate change and human rights, KlimaSeniorinnen provides a particularly powerful new tool for climate litigants and advances the rights-based approaches discussed in Chapter 7. The ECtHR incorporated all three forms of emerging best practice identified in that chapter into its decision: recognising the impacts that climate change is having and will continue to have on human rights; recognising that States must adopt and implement a wide range of climate actions to protect human rights; and referring to norms of international environmental law and best available science to interpret States’ human rights obligations in the climate context. On this point, ITLOS aligned with the first emerging best practice, albeit much less explicitly than the ECtHR, by acknowledging that ‘climate change represents an existential threat and raises human rights concerns’.⁸⁶ Given the ECtHR’s respected stature as a regional court focused on safeguarding human rights, as well as plaintiffs’ frequent invocation of Article 8 ECHR in European climate litigation, the Court’s approach in KlimaSeniorinnen will most likely have a significant positive impact on a range of rights-based cases.⁸⁷

19.4.7 Extraterritoriality

Both decisions highlight the global nature of climate change and the need to address it through national efforts and international cooperation, with due regard to extraterritorial impacts of actions under scrutiny. This recognition echoes the emerging best practice discussed in Chapter 8. The ITLOS Advisory Opinion’s emphasis on preventing transboundary pollution under Article 194(2) UNCLOS, which may require States to act with an even more stringent standard of due diligence than under Article 194(1),⁸⁸ is a particularly potent contribution to this emerging best practice.

The ECtHR, in contrast, may at first glance seem to have offered little in terms of guidance on climate change and extraterritoriality, other than stating in Duarte Agostinho that climate change does not warrant a special approach to jurisdiction.⁸⁹ However, in KlimaSeniorinnen the Court did take a globally oriented approach in its brief discussion on trade-related emissions. According to the Court, it would be ‘difficult, if not impossible, to discuss Switzerland’s responsibility for the effects of its GHG emissions’ on human rights ‘without taking into account the emissions generated through the import of goods and their consumption’, otherwise known as ‘embedded emissions’.⁹⁰ It acknowledged that embedded emissions ‘contain an extraterritorial aspect’⁹¹ and confirmed that this aspect fell within the scope of the case. While the Court did not examine the impact of these emissions in detail, its pronouncements provide important guidance to domestic courts and signal that the Court’s door is open to future cases addressing this dimension.⁹²

19.4.8 Duty of Care

Both decisions articulate specific positive obligations for States to adopt and implement a number of comprehensive measures to address climate change. To distil these obligations from relevant treaty texts, ITLOS and the ECtHR draw on a range of sources – most notably the UNFCCC and the Paris Agreement, but also principles of international environmental law and best available science. This line of judicial reasoning reflects emerging best practices discussed in Chapter 9, which demonstrates how judicial bodies can interpret treaties in a way that safeguards their effectiveness in a world existentially threatened by climate change.

19.4.9 International Atmospheric Trust

Although neither the ITLOS Advisory Opinion nor KlimaSeniorinnen directly engage with the application of the public trust doctrine in climate litigation, both decisions contain jurisprudence that could further international atmospheric trust cases. For example, the broad emphasis that ITLOS and the ECtHR place on intergenerational equity resonates with the emerging best practice described in Chapter 10. As the sovereign’s traditional duty is to protect trust resources for the benefit of current and future generations, the positive intergenerational equity jurisprudence in the ITLOS Advisory Opinion and KlimaSeniorinnen could strengthen the application of the public trust doctrine to non-traditional resources, such as the atmosphere. The ECtHR’s exploration of the role of domestic courts is notable in this context, given the synergies between the public trust doctrine and the protection of human rights,⁹³ as well as the fact that international atmospheric trust disputes have historically been adjudicated at the national level. This emphasis on domestic courts as key protectors of human rights could thereby encourage more judicial engagement with international atmospheric trust litigation.

19.4.10 Rights of Nature

While neither ruling expressly examines the rights of nature, the Tribunal’s consideration of the effects of climate change on the marine environment has an ecocentric quality that echoes the emerging best practice in Chapter 12. Most notably, the Tribunal frames its entire legal analysis within extensive IPCC findings on the myriad ways that climate change alters the ocean and the species that inhabit it.⁹⁴ When discussing States’ obligations under UNCLOS, the Tribunal reiterates that ‘climate change and ocean acidification affect virtually all forms of marine life, including fish and corals that build structures providing the habitat for large numbers of species’.⁹⁵ Such language furthers the belief that nature has intrinsic value and is deserving of protection independent of its worth to humans. The Tribunal’s finding that States have an obligation to conduct environmental impact assessments for activities that may harm the marine environment through GHG emissions seems aligned with this recognition.

19.4.11 International Law

Both ITLOS and the ECtHR built upon the emerging best practices described in Chapter 12 by relying on international climate change law to define the content of States’ obligations under UNCLOS and the ECHR, most notably the commitments made as Parties to the Paris Agreement. Moreover, principles of international environmental law, including the principles of due diligence, CBDR-RC, no-harm, prevention, and precaution, also substantively inform the scope of States’ respective duties. As a representative example, KlimaSeniorinnen requires States to keep their emissions reduction targets updated with due diligence,⁹⁶ while the ITLOS Advisory Opinion maintains that States have a stringent due diligence obligation to safeguard the marine environment from pollution⁹⁷ – which, as noted earlier, can be even more stringent in the context of preventing transboundary pollution.⁹⁸

19.4.12 Common but Differentiated Responsibilities and Respective Capabilities

The principle of CBDR-RC, much like the principle of due diligence described earlier, had an essential role in outlining States’ obligations pursuant to the respective treaties. In so doing, both decisions furthered the emerging best practice discussion in Chapter 13. In the ITLOS Advisory Opinion, the Tribunal explained that CBDR-RC requires both developed and developing States to make mitigation efforts to safeguard the marine environment from pollution, even if the measures taken vary by country.⁹⁹ This approach echoes the notion that, although developed nations must take the lead in terms of climate action, developing countries cannot focus strictly on climate adaptation. At the same time, it reinforces developed countries’ obligations to provide finance, technology transfer, and capacity building to enable ambitious climate action in developing countries.

Similarly, the ECtHR invoked and relied on the principle of CBDR-RC in finding that Switzerland had failed to comply with its obligations under Article 8. Whereas the requirement that States must quantify their overall remaining carbon budget for the time period until they reach carbon neutrality may appear to be largely procedural,¹⁰⁰ it is clear from the Court’s application of the obligation to Switzerland that it is not. Rather, it flows from the Court’s reasoning on this point that a State’s climate measures can only align with its duty to adopt and implement regulations capable of mitigating harmful climate impacts¹⁰¹ if they are based on the overarching long-term temperature goal of 1.5°C as well as that State’s fair share of the remaining global carbon budget. This conclusion is primarily supported by five points.

First, the Court maintained that the ECHR should be interpreted in harmony with the UNFCCC and the Paris Agreement,¹⁰² and it explicitly highlighted the central importance of CBDR-RC.¹⁰³ In this regard, the Court noted that each State ‘has its own share of responsibilities to take measures to tackle climate change and that the taking of those measures is determined by the State’s own capabilities rather than by any specific action (or omission) of any other State’.¹⁰⁴

Second, as explained earlier, States have a reduced margin of appreciation with respect to their climate commitments.¹⁰⁵ It follows then that States have limited discretion when it comes to the quantification of their climate targets and national carbon budgets in relation to the global 1.5°C temperature limit referenced by the Court, and that they are subject to strict judicial scrutiny for their conformity with the Convention.¹⁰⁶

Third, the Court explicitly rejected Switzerland’s efforts to justify its lack of a national carbon budget by positing that there is no established methodology to do so. To that end, the Court referenced the Neubauer decision, which similarly ‘rejected the argument that it was impossible to determine the national carbon budget, pointing to, inter alia, the principle of common but differentiated responsibilities under the UNFCCC and the Paris Agreement’.¹⁰⁷ The Court explained that ‘[t]his principle requires the States to act on the basis of equity and in accordance with their own respective capabilities’.¹⁰⁸ In other words, the Court held that States can determine their national carbon budget and that their methodology for doing so must be based on the principle of CBDR-RC. It also formulated equity as a guiding principle for such a determination. This is an explicit confirmation of the requirement that States determine their national carbon budget on the basis of a fair share determination, taking account of CBDR-RC, and grounded in principles of equity. Importantly, the Court tacitly acknowledged that an equal per capita emissions approach falls short of what is required under the principle of CBDR-RC, as it does not adequately account for States’ differing historical responsibilities and capabilities.¹⁰⁹ This underscores that methodologies used to determine national carbon budgets need to capture these different dimensions of CBDR-RC.

Fourth, the Court rejected Switzerland’s claim that its national climate policy – based on internal assessments and its nationally determined contributions – was similar in approach to establishing a national carbon budget.¹¹⁰ In doing so, it relied on the estimated remaining Swiss carbon budget to stay within 1.5°C, which was informed by evidence from the KlimaSeniorinnen association.¹¹¹ Based on this information, the Court noted that under its current climate strategy, Switzerland ‘allowed for more GHG emissions than even an “equal per capita emissions” quantification approach would entitle it to use’.¹¹² It is important to underscore that the Court did not suggest that meeting an equal per capita emissions standard would amount to compliance with its obligations; rather, it highlighted that Switzerland was exceeding even this insufficient standard, thereby evidencing a breach. The Court’s reference reaffirms that the equal per capita approach sets a baseline that is too low and does not fully reflect the higher standard required under CBDR-RC.

Fifth, the Court built on the earlier point and asserted that it ‘has difficulty accepting that the State could be regarded as complying effectively with its regulatory obligation under Article 8’ without ‘any domestic measure attempting to quantify the respondent State’s remaining carbon budget’.¹¹³

These points thereby infer that a State’s climate measures can only align with its duty to adopt and implement regulations capable of mitigating harmful climate impacts¹¹⁴ if they are based on the overarching long-term temperature goal of 1.5°C as well as that State’s fair share of the remaining global carbon budget. An equal per capita approach is insufficient in this context, as it fails to account for the differentiated responsibilities and capabilities of States, particularly those with greater historical emissions and higher capacities to reduce emissions.

19.4.13 Intergenerational Equity

Both ITLOS and the ECtHR promote the emerging best practice discussed in Chapter 14 by incorporating aspects of intergenerational equity into their decisions, thus bolstering the normative development of this international environmental law principle. For instance, the Advisory Opinion’s emphasis on protecting the ocean as an inherently valuable part of the environment – as opposed to a mere sink that absorbs emissions – requires States to introduce more ambitious climate policies that must, in turn, protect future generations. In the same vein, KlimaSeniorinnen frames States’ positive climate obligations under Article 8 ECHR around the need to ‘avoid a disproportionate burden on future generations’,¹¹⁵ thereby encouraging a fair distribution of climate obligations over time.

19.4.14 State Responsibility

Both decisions embody emerging best practice by explicitly rejecting the ‘drop in the ocean’ argument. This approach highlights that each State is required to do its own part to the best of its abilities to reduce greenhouse gas emissions, and especially resonates with the discussion in Chapter 15. ITLOS, for instance, specifically rejected the argument that climate change can only be regulated through ‘joint action’ and concluded instead that:

While the importance of joint actions in regulating marine pollution from anthropogenic GHG emissions is undisputed, it does not follow that the obligation under article 194, paragraph 1, of the Convention is discharged exclusively through participation in the global efforts to address the problems of climate change. States are required to take all necessary measures, including individual actions as appropriate.¹¹⁶

Similarly, in KlimaSeniorinnen, Switzerland had posited that climate change is a global phenomenon and that its GHG emissions, on their own, were not significant enough to represent an Article 8 ECHR violation.¹¹⁷ The Court pointed out that domestic courts have rejected this argument numerous times¹¹⁸ and further asserted that State responsibility is engaged when domestic authorities fail to take reasonable actions that could have mitigated the relevant harm:

Lastly, as regards the ‘drop in the ocean’ argument implicit in the Government’s submissions – namely, the capacity of individual States to affect global climate change – it should be noted that in the context of a State’s positive obligations under the Convention, the Court has consistently held that it need not be determined with certainty that matters would have turned out differently if the authorities had acted otherwise. The relevant test does not require it to be shown that ‘but for’ the failing or omission of the authorities the harm would not have occurred. Rather, what is important, and sufficient to engage the responsibility of the State, is that reasonable measures which the domestic authorities failed to take could have had a real prospect of altering the outcome or mitigating the harm […] In the context of climate change, this principle should also be understood in the light of Article 3 § 3 of the UNFCCC according to which States should take measures to anticipate, prevent or minimise the causes of climate change and mitigate its adverse effects.¹¹⁹

Thus, whether in the context of the marine environment or with respect to human rights, emerging best practice affirms that no State can escape its responsibility by pointing at a lack of action on the part of other States or to an alleged immateriality of its own contribution to global greenhouse gas emissions.

19.4.15 Causation

The Advisory Opinion and KlimaSeniorinnen further the emerging best practices outlined in Chapter 16 by taking a more flexible approach to causation that adapts to the complexities of the climate crisis. ITLOS, for example, acknowledged that causation in the transboundary context can be difficult to establish, but that reality did not prevent the Tribunal from determining that States still have an obligation to prevent transboundary pollution under Article 194(2) UNCLOS.¹²⁰

The ECtHR similarly observed that causation in climate change cases is challenging because, unlike in classic environmental disputes, the harm originates from a global problem, instead of a single source.¹²¹ Despite this complexity, the Court rejected Switzerland’s drop in the ocean argument as well as the strict ‘but for’ causation test, noting that ‘it need not be determined with certainty that matters would have turned out differently if the authorities had acted otherwise’; rather, what matters is whether authorities failed to take reasonable action that had ‘a real prospect of altering the outcome or mitigating the harm’.¹²²

With respect to attribution, the ECtHR highlighted the ‘critical lacunae’ in Switzerland’s climate policies, then explained that the actions implemented this decade would ‘have impacts now and for thousands of years’.¹²³ This approach aligns with the emerging best practice identified in Chapter 17 by expressly linking global climate impacts to failures in State climate policies.

19.4.16 Remedies

As Chapter 18 explained, providing an effective climate remedy is an essential part of addressing the harm caused by climate-related impacts. KlimaSeniorinnen’s declaratory judgment illustrates this approach (noting that advisory opinions do not order remedies). While the ECtHR stopped short of mandating more ambitious remedies, such as awarding just satisfaction or ordering general measures to prevent similar violations in the future, KlimaSeniorinnen’s declaratory relief should nevertheless promote systemic change that will fundamentally influence climate law and policy across Europe. Declaratory relief, moreover, falls in line with the Court’s standard approach to ECHR violations, its subsidiary role as a regional body, and the deference it traditionally grants to States to address breaches of the Convention.¹²⁴ In this regard, the outcome mirrors domestic approaches to remedies in other notable rights-based cases against governments, such as VZW Klimaatzaak v Kingdom of Belgium and Others,¹²⁵ where courts likewise drew a line in the sand while leaving details about implementation to be resolved by the other branches of government.

19.5 Implications for Key Issues in Climate Litigation

These landmark decisions have significant implications for climate litigation, from bolstering the ability of plaintiffs to hold States accountable for climate action to offering authoritative jurisprudence to courts in rights-based cases. This section examines the potential of the ITLOS Advisory Opinion and KlimaSeniorinnen to further accelerate and expand the field of climate litigation.

The ITLOS Advisory Opinion significantly strengthens the legal basis for climate action under UNCLOS. By clarifying States’ specific obligations related to GHG emissions and marine protection, it provides a robust framework for assessing State compliance and establishing State responsibility where compliance has been lacking.

The Opinion’s emphasis on due diligence, the precautionary principle, and the use of best available science potentially opens new avenues for legal challenges against States that fail to take adequate measures to reduce GHG emissions or protect the marine environment from climate impacts. Plaintiffs in those disputes will particularly benefit from the normative developments furthered by ITLOS, including States’ stringent due diligence obligations and the 1.5°C global temperature goal. As climate change litigation progressively evolves, the Opinion will also help inform courts’ judgments across jurisdictions, especially in disputes that invoke arguments related to marine pollution and associated activities. Furthermore, the Tribunal’s broad interpretation of marine pollution to include GHG emissions could influence other areas of international environmental law, potentially leading to more comprehensive legal approaches to addressing climate change globally.

KlimaSeniorinnen also stands to shift the climate litigation landscape significantly. As the ECtHR’s first climate change ruling, it will have immediate impact across Council of Europe Member States. Countries that do not adhere to their legal duty to put in place comprehensive climate policies will accordingly be liable for not safeguarding human rights. To that end, the new standing criteria for associations, as well as the ECtHR’s emphasis on the key role of domestic courts in climate litigation, should further unlock access to justice in climate disputes. Courts outside Europe, moreover, are likely to look to the KlimaSeniorinnen judgment for guidance as they adjudicate human rights claims. This persuasive impact will only grow as rights-based climate litigation continues to expand across the globe.

Although KlimaSeniorinnen left several topics open to interpretation, those questions will likely not remain unanswered for long. For instance, it remains to be seen precisely how the ECtHR will interpret its new standing criteria in the climate context for organisations more generally focused on human rights and/or environmental issues. Relatedly, more Article 8 jurisprudence would be helpful to ascertain the scope and content of States’ required regulatory framework. With six such cases pending before the ECtHR at the time of writing, the Court’s climate case law is just beginning.¹²⁶ The outcomes of those disputes will likely shed crucial light on the obligations established under KlimaSeniorinnen, which will benefit public authorities and stakeholders alike. Beyond those disputes, the ECtHR’s caseload will depend in part on the extent to which domestic courts provide access to justice in their respective jurisdictions and examine governments’ climate actions under the ECHR.

Finally, it is important to note here that a handful of cases discussed in this Handbook remain pending on appeal at the time of this writing and/or were overturned by courts of appeals or apex courts during the publication process. These include the landmark Milieudefensie and Others v Royal Dutch Shell,¹²⁷ which is pending in the Hague Court of Appeal following the district court ruling in favour of the plaintiffs, and Klimatická žaloba ČR v Czech Republic,¹²⁸ which was overturned by the Supreme Administrative Court of the Czech Republic and will be appealed by the plaintiffs.¹²⁹ Although the respective outcomes of these appeals remain uncertain at the time of writing, they illustrate that the timing of KlimaSeniorinnen comes at a pivotal juncture for the field of climate litigation.

19.6 Conclusion

The international decisions discussed in this chapter mark historic advancements in climate litigation. The ITLOS Advisory Opinion provides a robust framework for addressing climate change under UNCLOS and related customary international law, while the KlimaSeniorinnen judgment significantly advances human rights law as it pertains to the climate crisis. However, as this chapter has shown, both decisions also reflect and consolidate emerging best practices on a range of issues of broader relevance, including many of the issues discussed in this Handbook. Together, they represent a significant step forward in judicial engagement with climate change that could embolden judges around the world.

20 Conclusion The Future of Climate Litigation

Margaretha Wewerinke-Singh and Sarah Mead ^*

The preceding chapters have offered an extensive exploration of the rapidly evolving landscape of climate change litigation. The analysis across themes and issues shows how litigation has become a pivotal strategy for climate action, addressing the sluggish pace of policy development and minimal ambition of climate commitments within the legislative and executive branches of government. The Handbook as a whole also shows the snowball effect of climate litigation, with judicial dialogue spurring innovation in litigation strategies and judicial reasoning. Often drawing on landmark decisions in cases such as State of the Netherlands v Urgenda Foundation,¹ Milieudefensie v Shell,² Neubauer et al v Germany,³ Leghari v Pakistan,⁴ and Billy et al v Australia,⁵ an ever-growing number of rulings from judicial and quasi-judicial bodies around the world now underscores the potency of litigation in driving more ambitious and equitable climate policy and action. This trend has reached new heights with the groundbreaking decisions discussed in Chapter 19: the European Court of Human Rights (ECtHR) judgement in Verein KlimaSeniorinnen Schweiz and Others v Switzerland⁶ and the Advisory Opinion of the International Tribunal for the Law of the Sea (ITLOS) on climate change and marine protection.⁷

Through meticulous analysis of the emerging case law, each of the chapters has illustrated how climate lawsuits have cumulatively broken new legal ground and contributed to the evolution of legal systems worldwide, underscoring the resilience and adaptability of these systems in the face of climate change. Courts around the world have shown a particularly high degree of ingenuity through innovative applications of human rights and constitutional provisions, tort law, and principles such as public trust, as well as in grappling with questions of procedure and evidence.⁸ They have generally done so with an eye to how other courts have approached similar questions. The Urgenda decision, for example, has served as guidance for courts not just in other European jurisdictions⁹ but also further afield¹⁰ and at the international level.¹¹ The ECtHR decision in KlimaSeniorinnen further underscores the potential of strategic climate litigation to recalibrate institutional and policy responses to the climate crisis, with a distinct role for international bodies. Similarly, the ITLOS Advisory Opinion clarifies states’ obligations under the law of the sea in relation to climate change and, in doing so, advances many of the themes explored throughout this Handbook.

As Eckes, Nedevska, and Setzer show in their chapter, climate litigation has also pushed conceptual boundaries on justiciability. Courts around the world are increasingly assuming a more proactive role in safeguarding rights in the face of insufficient government action on climate change. These developments reveal the versatility of litigation as a strategy to break political inertia and ensure climate justice. The ECtHR and ITLOS decisions further reinforce this trend, with both judicial bodies demonstrating a willingness to engage with complex climate issues and enhance accountability for climate change and its consequences.

However, the transformative potential of climate litigation is far from being fully realised. With climate impacts exacerbating while legal landscapes evolve, new frontiers for strategic litigation are emerging. Realising the full potential of litigation as a catalyst for climate action will require persistent innovation in legal strategies coupled with collaboration across jurisdictions, social movements, scientific disciplines, and legal practitioners worldwide. This Handbook offers insights and perspectives to inform these continued efforts to further develop climate litigation as a force for climate justice.

20.1 Emerging Frontiers in Climate Litigation

20.1.1 Loss and Damage Litigation

One rapidly developing frontier is litigation focused on addressing climate change-induced loss and damage. Loss and damage encompasses the adverse impacts of climate change that occur despite mitigation and adaptation efforts.¹² These impacts span economic and non-economic losses, from loss of income and property damage to loss of cultural heritage, indigenous knowledge, biodiversity, and ecosystem services.¹³ A growing body of scholarship and practice highlights the human rights dimensions of these losses and damages, underscoring the need for global responses capable of preventing and minimising interferences with rights and redressing violations. Currently, the financial burden of addressing loss and damage lies almost exclusively with those affected.¹⁴ This inequity compounds existing vulnerabilities, perpetuating a cycle of poverty and susceptibility to climate impacts.¹⁵

The imperative of addressing loss and damage has gained increasing recognition, reflected most prominently in the inclusion of a standalone provision on loss and damage in the Paris Agreement, namely Article 8 (untitled).¹⁶ At the same time, however, progress towards a coordinated global response to address loss and damage remains minimal. While the 27th Conference of the Parties to the UNFCCC (COP27) held in 2022 culminated in an in-principle agreement to establish a new Loss and Damage Finance Facility,¹⁷ critical questions about the precise arrangements of this new fund remain unanswered. Moreover, the exclusion of liability and compensation from the scope of the Paris Agreement’s Article 8 arguably render this provision, as Broberg puts it, ‘without bite’, thus necessitating resort to ‘domestic as well as international legal regimes’ to rectify this shortfall.¹⁸

Against this backdrop, litigation is emerging as a pathway to enhance action and support for climate-vulnerable countries and communities grappling with compensable damages and/or irreversible climate impacts. As most cases focused on loss and damage are still pending, the potential of this type of litigation has not been fully revealed in this Handbook. However, it is clear from the broader body of climate caselaw that litigation – both domestically and internationally – does hold promise as a strategy for confronting loss and damage. For example, Mead and Doelle’s chapter suggests that potential cases could seek reparations for climate-related loss and damage based on primary rules such as the polluter pays principle, with Savaresi’s chapter setting out how such claims would be underpinned by secondary rules of state responsibility. Invoking human rights frameworks could also bolster claims for redress and compensation, as demonstrated by Wewerinke-Singh and Maxwell in their chapter on human rights.

For loss and damage litigation to deliver climate justice, the underpinning legal principles and remedies must integrate considerations of ethics, fairness, and equity.¹⁹ Liability and compensation frameworks emerging from litigation should reflect differential levels of responsibility for climate change so that the burden of addressing it is not inadvertently shifted to those who contributed only minimally to its causes. Overall, intelligently designed loss and damage litigation could significantly advance climate justice and provide legal pathways for those experiencing losses and damages to seek redress.

20.1.2 Litigation against Private Polluters

Strategic litigation against major corporate greenhouse gas emitters is another promising frontier, with the Milieudefensie v Shell ruling of the Hague District Court as a pioneering example of emerging best practice. Cases in this emerging frontier seek to hold private entities directly accountable for their significant contributions to climate change, unlike cases against governments which indirectly target corporate polluters through regulation. As scholars have noted, early lawsuits against private entities failed in part due to difficulties in attributing specific climate impacts to individual corporate actions.²⁰ However, as discussed by Phillips et al and Minnerop in their respective chapters, attribution science is progressing rapidly, enhancing prospects for successful polluter litigation. The enactment of laws establishing a due diligence standard for private actors in several parts of the world, both at the domestic and regional levels, further enhances these prospects.²¹

Another emerging strategy is pursuing polluters for deceptive practices obscuring the climate impacts of their products. This approach has already yielded some success in recent cases against fossil fuel companies.²² The deceptive practices of fossil fuel companies, including their intentional misleading of investors, regulators, and the public about climate science, were authoritatively established as fact by the Commission on Human Rights of the Philippines in its national inquiry on the responsibility of the world’s largest investor-owned fossil fuel companies for climate change-induced human rights violations in the Philippines.²³ Creative applications of litigation frameworks such as securities law, consumer protection law, and human rights law could expand avenues for private polluter accountability for climate change and its consequences.²⁴ Ambitious, coordinated lawsuits in multiple jurisdictions may overwhelm polluters’ legal defences and resources, thus potentially accelerating the transition to sustainable energy sources. Given the unparalleled contributions of major corporate polluters to the global climate crisis, further developing private polluter litigation is a climate justice imperative.²⁵ Moreover, such litigation seems indispensable for driving systemic shifts in corporate behaviour to curtail emissions, disincentivising climate misinformation campaigns, and encouraging economic practices that help rather than hinder the transition to just and sustainable societies.

20.1.3 More Diverse Litigation against Governments

As highlighted in the chapter by Connors et al, governments’ mitigation targets are ‘woefully insufficient’ to achieve the long-term temperature goal agreed by all States in the Paris Agreement.²⁶ The Global Stocktake in 2023 highlighted the gap between governments’ mitigation efforts and the scale of action needed to limit global warming to 1.5°C above pre-industrial levels, along with the ‘rapidly narrowing window to raise ambition and implement existing commitments’ in order to achieve this.²⁷ Litigation against governments targeting the ‘ambition’ of their mitigation targets is therefore likely to remain a focus in the coming years.

In addition, litigation is likely to target other problematic aspects of governments’ inadequate climate policies. For instance, while various countries have adopted more ambitious (albeit still insufficient) emission reduction targets in recent years, most are not on track to meet these targets.²⁸ If left unaddressed, these shortfalls in implementation are a likely target for future litigation. Concerns around the (lack of) transparency and feasibility of governments’ climate policies, including in connection with widely adopted but often poorly operationalised net-zero targets, are also likely to trigger further claims.²⁹

Again, the contributions from the ECtHR and ITLOS are likely to reinforce these trends. The ECtHR’s establishment of specific positive obligations for states under the European Convention on Human Rights provides a detailed framework for challenging government inaction on climate change. Similarly, the ITLOS Advisory Opinion’s clarification of states’ obligations under the UN Convention on the Law of the Sea (UNCLOS) opens up new possibilities for litigation focused on marine protection and climate change. These decisions will undoubtedly serve as blueprints for new cases in other jurisdictions and under different legal regimes.

20.1.4 Interlinkages between Climate Change, Biodiversity, and Rights of Nature

The intricate relationship between climate change and biodiversity loss is crystallising in science, policy, and law.³⁰ Climate change is a direct driver of biodiversity decline, while ecosystem degradation exacerbates climate change impacts.³¹ Consequently, legal approaches integrating climate change and biodiversity protection are emerging, including in litigation.

Some countries have enacted legal frameworks recognising the interconnectedness between climate and biodiversity.³² Litigation defending biodiversity through a climate lens represents largely uncharted legal territory holding immense potential. Lawsuits could invoke biodiversity protection laws to challenge fossil fuel expansion projects that would exacerbate climate change and endanger ecosystems. Opportunities also exist for creative lawsuits using climate laws to prevent activities threatening biodiversity. Successfully establishing legal responsibility for biodiversity impacts resulting from climate change would be groundbreaking. Exploring interconnected climate and biodiversity impacts in lawsuits could ultimately foster more holistic legal approaches addressing these twinned global crises.

Further developments around rights of nature could drive and accelerate evolution in this area. As Borràs-Pentinat’s chapter demonstrated, lawsuits invoking the rights of nature and legal decisions recognising such rights emphasise the potential of fostering sustainable and meaningful relationships between humans and the natural world. These lawsuits and decisions align with the shifting ethical paradigm underlying rights of nature – from conceiving nature as property to recognising its inherent value. Landmark judgments such as Future Generations v Ministry of the Environment and Others³³ show the transformational potential of climate litigation upholding nature’s rights, potentially redefining legal systems’ relationship with the natural world. Although nascent, strategic litigation centred on interconnected human, climate, and biodiversity considerations, as well as the rights of nature, represents a highly promising approach for multi-species climate justice.

The ITLOS Advisory Opinion reinforces the importance of these interlinkages, particularly in the context of marine ecosystems. By drawing legal conclusions from the demonstrated impacts of climate change on marine biodiversity, it provides a legal basis for integrating climate and biodiversity considerations in future litigation strategies.

20.1.5 Inter-State Climate Litigation

As Mead and Doelle’s chapter unveiled, international law has significant potential when applied more fully in climate adjudication. Savaresi’s chapter underscores this potential, with the analysis of state responsibility signalling that inter-state climate litigation could profoundly shape international climate politics and law. In essence, the cross-border nature of climate change means states are increasingly facing transboundary harms. The acts and omissions of states causing these harms potentially breach the no-harm rule, the principle of prevention, and a wide range of other obligations of states under international law.³⁴ The chapter recognises that inter-state climate lawsuits face barriers, including procedural obstacles and uncertainties around the exact scope and content of applicable international norms. However, the ITLOS’ clarification of states’ obligations under UNCLOS has significantly reduced this uncertainty, with the forthcoming advisory opinions on climate change obligations and legal consequences from the International Court of Justice and the Inter-American Court of Human Rights poised to further strengthen the foundations for inter-state climate claims.

Once procedural obstacles are overcome, inter-state climate lawsuits could lead to further crystallisation of states’ obligations related to climate change under international law. Resulting judgments may also provide grounds for affected states to claim reparations for climate damages. This type of inter-state climate litigation would be unprecedented, with potentially major implications for international cooperation and climate governance. Ultimately, realisation of this frontier hinges on visionary legal interpretation aligned with foundational legal norms and principles, most notably including the jus cogens right of self-determination and other fundamental rights. Pioneering cases centred on the protection of the rights of peoples at the climate frontlines may be essential to unlock the radical potential of inter-state climate litigation.

20.2 Concluding Thoughts

Climate change is an existential threat demanding urgent and unprecedented action across all levels of society. As this Handbook illustrates, climate litigation has emerged as a vital strategy for catalysing such action. At the same time, the emerging best practice discussed in this Handbook highlights the potential of strategic climate litigation to recalibrate institutional and policy responses to the climate crisis. Often, this is achieved by demanding the fulfilment of existing state duties and the enhancement of corporate accountability. Realising this potential more fully will require sustained creativity, ambition, and collaboration among communities of practice worldwide.

Taking a bird eye’s view, it seems no exaggeration to say that climate change necessitates reimagining legal systems and firmly upholding – or even expanding – notions of justiciability. As several of the contributions to this Handbook have also shown, it is essential that principles of equity and human rights inform these processes of legal evolution and innovation. Commitment to these fundamental legal norms, alongside tireless persistence from civil society and the legal community, will determine the success of climate litigation in delivering climate justice. Borràs-Pentinat’s chapter further reminds us of the power of legal imagination, with the evolving jurisprudence on the rights of nature representing perhaps the most apt illustration of transformational legal reasoning capable of confronting narratives and norms that have helped facilitate the climate crisis.

This Handbook represents, we hope, a milestone in the evolving scholarly discourse and legal practice in the field of climate litigation. But it is also an invitation to further scholarly analysis. As the field continues innovating, additional perspectives highlighting promising developments, nascent strategies, and emerging issues will be needed. We hope this Handbook provides inspiration for scholars, practitioners, and concerned citizens around the world to boldly engage in this agenda-setting area of legal scholarship and practice. With the stakes higher than ever, the global quest for climate justice – through litigation and other means – must press on.