Part III - Regime Interaction and Interpretation

12 International Law

Sarah Mead and Meinhard Doelle *

12.1 Introduction

The nature of climate change as an urgent global problem renders international law a logical source of guidance in climate litigation. A survey of case law to date reveals that litigants and courts frequently draw on international law, particularly the UN Framework Convention on Climate Change (UNFCCC or the Convention) and the Paris Agreement, in climate change litigation. This has fostered a global judicial dialogue regarding the interpretation of States’ obligations under international law.

This chapter explores how courts around the world have treated international law in climate litigation. Beginning with an introduction to the international legal instruments most frequently invoked in climate litigation and their usage by courts, the chapter proceeds with a descriptive section on general trends and approaches (Section 12.2), followed by an analytical section that identifies emerging best practices and explains why it qualifies as such (Section 12.3). Subsequently, the chapter discusses the issue of replicability (Section 12.4) and concludes with some final thoughts.

In line with the overall approach of the Handbook, this chapter focuses on case law that offers helpful lessons for judges and litigants. For this chapter, such a selective approach is also necessitated by the sheer volume of potentially relevant case law. The primary focus is on how courts have engaged with international environmental law, particularly international climate change law. While international human rights law is also frequently invoked in climate litigation, it is addressed in detail in Chapter 7.

12.1.1 International Climate Change Law

International climate change law encompasses a ‘complex web of principles, rules, regulations and institutions’.¹ At its core sit three treaties: the UNFCCC,² the Kyoto Protocol,³ and the Paris Agreement. These treaties are supplemented by a vast array of principles that comprise international environmental law and intersect with various other fields of international law, in particular international human rights law. This section provides a brief overview of the two main treaties now in operation – the UNFCCC and the Paris Agreement – to provide context for the subsequent discussion.

Adopted in 1992, the near universally ratified UNFCCC aims ‘to achieve, in accordance with the relevant provisions of the Convention, stabilization of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system’.⁴ The Convention sets out various commitments for States towards achieving this objective,⁵ such as developing national inventories of greenhouse gas (GHG) emissions and formulating national and regional programmes to mitigate GHG emissions and facilitate adaptation.⁶ Additionally, developed countries ‘commit themselves specifically’ to adopting national policies and taking measures to reduce GHG emissions.⁷ The Convention establishes several principles to guide State action ‘to achieve the objective of the Convention and to implement its provisions’⁸ including common but differentiated responsibilities (CBDR), intergenerational equity, precaution, the special circumstances of developing countries, and sustainable development.⁹

The Paris Agreement, adopted in 2015, seeks to enhance the implementation of the Convention and ‘strengthen the global response to the threat of climate change’.¹⁰ To that end, it aims to hold ‘the increase in the global average temperature to well below 2°C above pre-industrial levels and pursu[e] efforts to limit the temperature increase to 1.5°C above pre-industrial levels’.¹¹ The Agreement covers several action areas: mitigation, adaptation, loss and damage, and finance,¹² but it is the provisions relating to mitigation that have proven most relevant to climate litigation to date. Under the Agreement, State parties ‘must prepare, communicate and maintain successive nationally determined contributions’ (NDCs) and pursue domestic mitigation measures ‘with the aim of achieving the objectives’ of their NDCs.¹³ In terms of content, NDCs are to reflect parties’ ‘highest possible ambition’ towards achieving the Agreement’s objectives,¹⁴ with developed country parties continuing to take the lead by setting economy-wide absolute emission reduction targets and providing support for developing country parties.¹⁵ Setting the regime’s ‘direction of travel’,¹⁶ the Agreement also requires that updates of NDCs ‘represent a progression’ over time in terms of ambition, taking into account the outcome of the global stocktake.¹⁷

In addition to these treaties, climate litigation frequently invokes international environmental law principles such as harm prevention,¹⁸ precaution,¹⁹ intergenerational equity,²⁰ and sustainable development.²¹

12.1.2 International Law Before National Courts

The treatment of international law by national courts formally depends on the legal system within which the litigation takes place. Legal systems are often categorised as monist or dualist. A monist system treats international law as automatically incorporated into national law (incorporation), while a dualist system treats international law as an external body of law that requires transformation into national law, typically through legislative action (transformation).²² In practice, this distinction is more nuanced: various rules, including those applied by courts, modify how international law is received into the domestic legal system.²³ The result is a ‘moderation of the opposing main positions of incorporation and transformation’, softening the stark contrast between the two approaches and yielding similar outcomes despite differences in local constitutional set-ups.²⁴

An evolution in the nature of international law has expanded the role of national courts in interpreting and applying international law. Traditionally, international law primarily focused on relations between States, leaving a limited role for national courts.²⁵ Modern international law, by contrast, is often described as ‘inward-looking’ as it concerns the internal affairs of States.²⁶ This shift is most evident in international human rights law but can also be seen in the field of international environmental law. The so-called ‘bottom up’ structure of States’ mitigation obligations under the Paris Agreement, whereby contributions are ‘nationally determined’, showcases this shift.²⁷ As Wegener explains:

Although the Paris Agreement does not contain substantive provisions comparable with the mitigation provisions of the Kyoto Protocol, it nonetheless sets up a normative architecture of internationally agreed standards and expectations. These are in need of translation into domestic governance and, finally, domestic action. While this may be primarily a task for legislatures, domestic courts can contribute by ‘holding their governments to account, and … ensuring that … commitments are given practical and enforceable effect’. Rather abstract provisions, such as the collective temperature goal, which are not directly justiciable, are given practical effect when invoked in domestic courts… Moreover, by referring to the non-binding standards set by the Paris Agreement and NDCs, national courts help to strengthen the legitimacy of those standards.²⁸

12.2 Case Law Development: State of Affairs

A review of the case law to date demonstrates that courts usually rely on international law indirectly in climate litigation to interpret standards under national law, rather than applying international law directly. The most common source of norms are the UNFCCC and the Paris Agreement, specifically the collective goals, principles, and individual mitigation commitments contained therein. Often looking beyond whether a commitment or obligation is binding per se in international law, courts are asking questions such as:

• Has the government committed (in law or policy) to implementing the commitment or obligation?

• Is the commitment or obligation relevant in defining the government’s duty to its citizens under domestic tort law, human rights law, or environmental law?

• Is the commitment or obligation helpful in defining the powers, duties, and functions of government decision-makers when making policy or decisions that might support or hinder efforts to meet the commitment?

The case law also shows an emerging distinction – whether justified or not – between common and civil law courts in the treatment of international law.

The Urgenda case illustrates how courts can draw on international law both directly and indirectly in the context of climate litigation.²⁹ In 2019, the Supreme Court of the Netherlands ruled that the Dutch government must take measures to reduce emissions in the country by at least 25 per cent below 1990 levels by 2020. The Court relied directly on international law in the form of the European Convention on Human Rights (ECHR), which has a direct effect in the Netherlands, as the source of the breached obligation.³⁰ After determining that climate change poses a real and foreseeable risk of harm under Articles 2 and 8 of the ECHR, the Court concluded that the State had a positive obligation to take reasonable and adequate measures to address that risk.

The Supreme Court indirectly utilised various norms of international law to determine the scope of the State’s obligation under the ECHR. For example, the Court referred to international law (i.e. the UNFCCC, the no harm principle, and the international law on state responsibility) to determine that the State had an individual responsibility to mitigate climate change, despite it being a global problem.³¹ The Court then drew on both hard and soft norms of international law to determine the minimum amount by which the State must reduce its GHG emissions as a way of ‘concretising’ the obligation, including UNFCCC provisions, Conference of the Parties (COP) decisions, Intergovernmental Panel on Climate Change (IPCC) reports, EU law, and international environmental law principles such as the precautionary principle.³² The Supreme Court concluded that ‘there is a high degree of consensus in the international community on the need for … Annex 1 countries to reduce greenhouse gas emissions by 25 per cent to 40 per cent by 2020’,³³ with the lower limit representing the ‘absolute minimum’ for the State to discharge its positive obligations under Articles 2 and 8 of the ECHR.³⁴

The approach of drawing on international law indirectly to interpret open standards at the national level is particularly evident in European case law. For example, the Brussels Court of First Instance in the Belgian case of Klimaatzaak drew on a range of international law norms to determine whether the respondent governments had breached their obligations under the ECHR – as per the Dutch courts in Urgenda.³⁵ The Council of State in the French case of Grande-Synthe did the same. The case, which was brought by a coastal municipality (Grande-Synthe) and its mayor, argued that the French Government was not doing enough to combat climate change. The Council of State ultimately limited its review to whether the State was complying with its own climate mitigation target to reduce GHG emissions by 40 per cent by 2030 compared to 1990. This was based on its view that the plaintiffs could not rely directly upon the UNFCCC and the Paris Agreement to challenge the government’s inaction. The Council of State nevertheless was clear that the State’s obligations under international law were relevant to interpreting national law. The Council of State explained:

According to these stipulations and provisions, the European Union and France, as signatories of the UNFCCC and the Paris Agreement, have committed to combating the harmful effects of climate change caused notably by the increase, during the industrial era, in greenhouse gas emissions attributable to human activities, by implementing policies aimed at reducing the level of these emissions in gradual stages, in order to assume, based on the principle of an equitable contribution by all states parties to the objective of reducing greenhouse gas emissions, their common but differentiated responsibilities according to their contribution to the level of emissions and their capacity and resources for reducing them in the future, in light of their level of economic and social development. While the stipulations of the UNFCCC and the Paris Agreement cited in point 9 require further actions to be taken to produce effects in respect of individuals and accordingly, do not have any direct effect, they must nevertheless be taken into consideration in interpreting the provisions of national law, notably those cited in point 11, which, in referring to the targets they set, are specifically aimed at their implementation.³⁶

Civil law courts outside of Europe have engaged with international law in a similar way. The Supreme Court of Colombia in the case of Future Generations identified a broad range of ‘hard and soft law’ instruments ‘which constitute a global ecological public order and serve as guiding criteria for national legislation’.³⁷ Among the most relevant instruments identified were the International Covenant on Economic, Social and Cultural Rights, the Stockholm Declaration, and the Paris Agreement. The decisions in Leghari and Shrestha, two landmark cases from Pakistan and Nepal respectively, also draw liberally on international environmental law to inform the interpretation of the relevant domestic law provisions of human rights law – as discussed in more detail in Section 12.1.2.³⁸

By contrast, common law courts have taken a more cautious approach to using international law in the context of climate litigation. This is evident in the Australian case of Sharma. The case was brought by eight young people who sought an injunction to prevent the Minister from approving a coal mine extension. Reversing the first instance decision, the Full Federal Court of Australia ultimately found that the Minister did not owe the youth plaintiffs a duty of care. In coming to its decision, the Court (in three separate judgments) did not consider the climate treaty regime relevant to determining the standard of care. While acknowledging that the relevant Act ‘is founded in significant part on the translation of international agreements into Commonwealth law’, Allsop CJ reasoned that the relevant international agreements had not been ‘translate[d]’ into domestic law – referring to the dualist orientation of the Australian legal system.³⁹

The UK Supreme Court in the Heathrow Extension case adopted a similar approach. The case challenged the legality of the UK Government’s Airport National Policy Statement, which gave in-principle support to the extension of Heathrow Airport. Among the claims, Plan B argued that the Government’s commitment to the Paris Agreement was part of ‘government policy’, and that the Government had therefore breached Section 12.5(8) of the Planning Act. The Court found that the reference to ‘government policy’ in the Planning Act excluded the Paris Agreement, noting:

The fact that the United Kingdom had ratified the Paris Agreement is not itself a statement of Government policy in the requisite sense. Ratification is an act on the international plane. It gives rise to obligations of the United Kingdom in international law which continue whether or not a particular government remains in office and which, as treaty obligations, ‘are not part of UK law and give rise to no legal rights or obligations in domestic law’.⁴⁰

The distinction between civil and common law courts does not, however, provide clear direction as to how national courts approach international law. In the New Zealand case of Thomson, the High Court applied the presumption of consistency to interpret the scope of the Minister’s discretion in setting the country’s emissions reduction targets.⁴¹ Under the Climate Change Response Act, the Minister had the power to set, amend, or revoke New Zealand’s climate targets at any time. The plaintiff challenged the Minister’s failure to review the 2050 target following the release of the IPCC’s Fifth Assessment Report (AR5). The Court ultimately dismissed the application for judicial review. However, it found that the Minister was required to review the 2050 target following the release of AR5 in order to ‘give effect to the Act, and what New Zealand ha[d] accepted, recognised and committed to under the international instruments’.⁴² In doing so, it made an important pronouncement:

The Paris Agreement has been entered into in ‘pursuit of’ the Convention’s objective and guided by its principles. As a matter of statutory interpretation, s 224(2) can and therefore must be interpreted consistently with New Zealand’s international obligations under these instruments. I consider s 224(2) is also to be interpreted consistently with matters that New Zealand has recognised and accepted in these instruments, as these aid in interpreting our obligations.⁴³

In the Australian case of Rocky Hill,⁴⁴ the Court similarly considered the Paris Agreement as a factor to be considered when deciding whether to grant approval for the proposed mine. In reaching its decision to deny approval for the mine, the Court noted that – although the Paris Agreement did not prohibit new coal mine approvals –:

the exploitation and burning of a new fossil fuel reserve, which will increase GHG emissions, cannot assist in achieving the rapid and deep reductions in GHG emissions that are necessary in order to achieve ‘a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of this century’ (Article 4(1) of the Paris Agreement) or the long term temperature goal of limiting the increase in global average temperature to between 1.5C and 2C above pre-industrial levels

(Article 2 of the Paris Agreement).⁴⁵

In a limited number of cases, there is a conspicuous lack of references to the role of international law. For example, in the United States, neither the majority nor dissenting opinions in the appeal judgment in the Juliana case refer to international law in their reasoning, despite its obvious relevance.⁴⁶

12.3 Emerging Best Practice

12.3.1 Utilising International Law to Interpret National Law Standards

The most important element of emerging best practice in case law to date is the critical role international law, including non-binding soft law norms, can play in shaping domestic law through the act of interpretation. Where the duty of care being invoked in a case involves an open standard or open-textured norm, jurisprudence shows how courts have employed international law to provide substance or content to those standards. Although the source of the duty differs from case to case, a consistent factor is the use of international law norms to establish the standard against which the act or omission in question is assessed.

The Urgenda case exemplifies this. While the District Court ruled that Urgenda could not rely on international law directly, it recognised that international law still has a ‘reflex effect’ in national law, in this instance, to interpret the standard of care related to the tort of hazardous negligence. The Court explained:

[I]t follows that an international-law standard – a statutory provision or an unwritten legal standard – may not be explained or applied in a manner which would mean that the state in question has violated an international-law obligation, unless no other interpretation or application is possible. This is a generally acknowledged rule in the legal system. This means that when applying and interpreting national-law open standards and concepts, including social proprietary, reasonableness and propriety, the general interest or certain legal principles, the court takes account of such international-law obligations.⁴⁷

The Supreme Court also utilised a broad range of international law norms to interpret the ECHR, which formed the basis of its decision. In the Court’s view, any interpretation of the ECHR ‘must … take into account … relevant rules of international law’ and state practice, in accordance with the jurisprudence of the European Court of Human Rights.⁴⁸ This was consistent with Article 31(3) of the Vienna Convention on the Law of Treaties which notes that ‘any relevant rules of international law applicable in the relations between the parties’ shall be taken into account when interpreting a treaty. The District Court and the Supreme Court therefore ultimately used international law to similar effect, despite the different bases for their decisions.⁴⁹

12.3.2 International Law and the ‘Greening’ of Human Rights

The interconnected nature of international environmental law and international human rights law is well established in national, regional, and international jurisprudence. As human rights law increasingly forms the basis for climate cases, courts are adopting the best practice of drawing on international environmental law to define the scope and content of those human rights obligations.

In the Asghar Leghari case, a Pakistani farmer complained that the Government had failed to implement its own climate change policies, which constituted a breach of his constitutional rights. In its judgment, the Court drew on a variety of international environmental law principles to interpret the scope of the relevant rights. The Court explained:

Fundamental rights, like the right to life (Article 9) which includes the right to a healthy and clean environment and right to human dignity (Article 14) read with constitutional principles of democracy, equality, social, economic and political justice include within their ambit and commitment, the international environmental principles of sustainable development, precautionary principle, environmental impact assessment, inter and intra-generational equity and public trust doctrine. Environment and its protection has taken a center stage in the scheme of our constitutional rights. It appears that we have to move on. The existing environmental jurisprudence has to be fashioned to meet the needs of something more urgent and overpowering ie Climate Change.⁵⁰

Similarly, in the case of Shrestha, the Supreme Court referred to the UNFCCC, the Kyoto Protocol, and the Paris Agreement when determining that the State had not fulfilled its constitutional obligations to protect the petitioner’s right to life with dignity and a clean environment.⁵¹ The case was brought by a Nepalese lawyer, Padam Bahadur Shrestha, who alleged that the Government’s failure to set and implement adequate climate law and policies breached his rights under the Constitution and violated Nepal’s commitments under the UNFCCC and the Paris Agreement. Finding in favour of the plaintiff, the Court found that ‘a new law dealing with climate change adaptation and mitigation, ensuring environmental justice while taking measures for maintaining clean environment with environmental conservation, and regulating production that causes impact on food, species, and ecosystem, and health seems imperative’. In addition to being necessary to protect constitutional rights, the Court noted that such a law ‘would also facilitate in effectuating the commitments under the Paris Agreement on Climate Change, 2015’.⁵²

The Brazilian case, PSB et al v Brazil (on Climate Fund), represents a significant development in the greening of human rights. The case concerned the administration of the National Climate Fund (Fundo Clima) which had been created by law but inoperative for several years. The Supreme Court found that the executive branch has a constitutional duty to execute and allocate the funds of the Climate Fund to mitigate climate change, based on both the separation of powers and the constitutional right to a healthy environment. In this context, it determined that environmental treaties, including the Paris Agreement, ‘are a species of the genus human rights treaties and enjoy, for this reason, supranational status’.⁵³ This means that any Brazilian law or decree that contradicts the Paris Agreement, including the NDC, may be invalidated. In coming to this view, the decision recalls the statement made by a UN Environment Programme representative during the hearing that ‘[t]here are no human rights on a dead or sick planet’.⁵⁴

The interconnected relationship between environmental protection and human rights is also reflected in the jurisprudence at the regional and international levels. The Inter-American Court of Human Rights (IACtHR), in its landmark Advisory Opinion No 23, noted ‘the existence of an undeniable relationship between the protection of the environment and the realization of other human rights, in that environmental degradation and the adverse effects of climate change affect the real enjoyment of human rights’.⁵⁵ It accordingly concluded that it could ‘avail itself of the principles, rights and obligations of international environmental law’ when determining the scope of the State’s obligations under the American Convention.⁵⁶

Turning to the international level, the Committee on the Rights of the Child similarly drew on international environmental law in its Sacchi decision. The complaint was brought by sixteen children from around the world who alleged that their rights under the Convention on the Rights of the Child had been violated due to insufficient mitigation and adaptation action on the part of the respondent States. The Committee ultimately found the complaint to be inadmissible for failing to exhaust domestic remedies. The Committee’s decision nevertheless shows the relevance of international environmental law to interpreting international human rights law. For instance, in determining the State’s individual responsibility for the harm that may arise as a result of its GHG emissions, the Committee drew on the Paris Agreement and the principle of CBDR.⁵⁷ The Committee also pointed to the UNFCCC and the Paris Agreement as evidence that the respondent States were aware of the potential harm associated with their GHG emissions.⁵⁸

12.3.3 Range of International Law Norms, Including Soft Law

Emerging best practices in climate litigation involve courts relying on a broad range of international law norms when adjudicating climate cases. These norms include international treaty law (e.g. the UNFCCC and the Paris Agreement), general principles of international environmental law (e.g. the principles of precaution and no harm), and soft law instruments (e.g. decisions of COP and the UN Guiding Principles).

A groundbreaking aspect of the Shell decision was its use of human rights law, including soft law, to interpret the standard of care applicable to a company in its global operations – in this case, Royal Dutch Shell. The plaintiff, a Dutch NGO called Milieudefensie, relied on the same provision of the Dutch Civil Code in combination with Articles 2 and 8 of the ECHR as in the Urgenda case. The case alleges that Royal Dutch Shell has violated its duty of care by failing to adopt policies that will reduce the company’s emissions in line with the Paris Agreement’s long-term temperature goal. Finding in favour of the plaintiffs, the Court ordered Shell to reduce its emissions by 45 per cent by 2030 relative to 2019 (roughly in line with the global average) across all of its activities, including both its own emissions and end-use emissions.⁵⁹ In its interpretation of the standard of care, the Court treated the non-binding goals of the Paris Agreement as ‘a universally endorsed and accepted standard that protects the common interest of preventing dangerous climate change’.⁶⁰ It also considered the protections afforded by international human rights law, including the International Covenant on Civil and Political Rights and the ECHR. While acknowledging that human rights law does not give rise to binding obligations on Shell (as a non-State actor), the Court considered human rights to be important – also given the extent of Royal Dutch Shell’s emissions which exceed that of the Netherlands. The Court noted that ‘[d]ue to the fundamental interest of human rights and the value for society as a whole they embody, human rights may play a role in the relationship between Milieudefensie et al. and RDS. Therefore, the court will factor in the human rights and the values they embody in its interpretation of the unwritten standard of care’.⁶¹ The Court also cited various soft law instruments, including the UN Guiding Principles on Business and Human Rights (UNGPs), to support its finding that companies must respect human rights. The reliance on these sources did not depend on the company having endorsed them, nor a finding that these sources were binding on the jurisdictions in which Shell operates.

The Commission on Human Rights of the Philippines adopted a similar approach in its decision relating to the Carbon Majors inquiry.⁶² The inquiry assessed the responsibility of the ‘Carbon Majors’ – i.e. those corporations that have historically contributed the most to climate change – for human rights violations arising from climate impacts in the Philippines. In its decision, the Commission found that enterprises ‘must comply with the Nationally Determined Commitments of States who are parties to the Paris Agreement’, as a result of their obligations under the UNGP to respect the principles of international human rights.⁶³ The Commission therefore relied on the UNGP to establish not only the responsibility of enterprises towards human rights but also the duty of States to regulate the activities of enterprises in accordance with international human rights obligations.

12.3.4 International Law as Relevant to Determining the Minimum Standard

It is emerging best practice for courts to use a combination of international law and the best available science to determine the minimum standard (of care) that, for example, a government must meet to fulfil its legal duties. This is particularly relevant in cases which require a court to determine whether a State’s mitigation policies are sufficient to meet its ‘fair share’ of global emissions reductions. Courts have generally acknowledged that the UNFCCC, the Paris Agreement, and the IPCC science reports do not themselves set a precise standard against which to assess States’ mitigation policies. Nevertheless, courts have been willing to set conservative minimum standards based on the international consensus reflected in these sources.⁶⁴

The German Neubauer case serves as a useful illustration of this emerging best practice. The case concerned a legal challenge to Germany’s Federal Climate Protection Act on the basis that the mitigation target contained therein violated the youth plaintiffs’ human rights, as protected under the German Constitution. The Court approached the complaint from two angles: firstly, asking whether the Act violated the State’s duty to protect (i.e. as a breach of a positive duty) and secondly, asking whether the Act violated the State’s duty not to interfere with fundamental freedoms (i.e. a breach of a negative duty).⁶⁵ In relation to the first question, the Court found that the dangers presented by climate change are sufficiently real and serious to give rise to a duty to protect under the German Constitution. Given the wide margin afforded the State in relation to positive duties, however, the Court did not consider that any such duty had been breached in the present case as the approach adopted in the German Act was not ‘manifestly unsuitable or completely inadequate’.⁶⁶ The Court did, however, find that the State had breached its negative duty not to interfere with the fundamental freedoms of the complainants in the future. In the Court’s view, Article 20a of the Constitution concerning the protection of the natural foundations of life and animals requires the government to take climate action.⁶⁷ While the government has ‘considerable leeway’ to design the content of its climate action, the Court considered that its role was to ‘review whether the boundaries of Article 20a are respected’.⁶⁸ International law played a key role in determining those boundaries. The temperature limit set out in the Act – which reflected that in the Paris Agreement – was identified ‘as providing fundamental orientation for climate action’.⁶⁹ The Court explained:

Rather than being purely an expression of political will, the chosen temperature limit must indeed also be understood as being a specification of the climate action required under constitutional law. This is primarily supported by the fact that the climate target specified in [the Act] is the internationally agreed temperature limit of Article 2(1)(a) Paris Agreement, which the legislator has deliberately and explicitly taken as a basis. Its constitutional law significance goes beyond the consent given by the German legislator to the Paris Agreement in passing the act of approval. The fact that the Paris target is explicitly named as the basis of Germany’s Federal Climate Change Act is closely related to the obligation to take climate action arising from Article 20(a) GG. Due to the genuinely global dimension of climate change, the state can ultimately achieve the objective of slowing down climate change enshrined in Article 20(a) GG only through international cooperation. It has taken action to this end by ratifying the Paris Agreement, which provides the framework within which it is now also fulfilling its more extensive climate action obligations arising from Article 20(a) GG […]. By adopting the temperature limit of Article 2(1)(a) Paris Agreement, the legislator has set the fundamental course of national climate change law in a direction that gives the German state an opportunity to effectively fulfil its constitutional mandate to take climate action through its own efforts embedded within an international framework.⁷⁰

Reliance on best available science when assessing obligations relating to climate change can also be considered a requirement derived from international law. The Paris Agreement’s preamble recognises ‘the need for an effective and progressive response to the urgent threat of climate change on the basis of the best available scientific knowledge’, while Article 4(1) refers to the need for emissions to peak and for parties ‘to undertake rapid reductions thereafter in accordance with best available science’.⁷¹ The Glasgow Climate Pact (2021) further recognises ‘the importance of the best available science for effective climate action and policymaking’⁷² and the need for ‘accelerated action in this critical decade, on the basis of the best available scientific knowledge and equity’.⁷³

The New Zealand case of Thomson (discussed earlier) linked the need to rely on best available science with the government’s obligations under international law. Under the Climate Change Response Act, there was no express requirement for the Minister to review the 2050 target following the release of a new IPCC Assessment Report. However, the Court found that there was an implied mandatory consideration to give effect to the Act and New Zealand’s international commitments.⁷⁴ In the Court’s view, the provisions of the climate treaty regime together ‘underline the pressing need for global action, that global action requires all Parties individually to take appropriate steps to meet the necessary collective action, and that Parties should do so in light of relevant scientific information and update their individual measures in light of such information’.⁷⁵ The Court therefore concluded:

The IPCC reports provide the most up to date scientific consensus on climate change. New Zealand accepts this. To give effect to the Act and what New Zealand has accepted, recognised and committed to under the international instruments, and in light of the threat that climate change presents to humankind and the environment, I consider the publishing of a new IPCC report requires the Minister to consider whether a target set under s 224 should be reviewed. That is, it is a mandatory relevant consideration in whether an existing target should be reviewed under s 224(2).⁷⁶

12.3.5 International Law as Relevant to Interpreting Statutory Discretion

Finally, courts have shown a willingness to draw on international law when interpreting the scope of a statutory discretion – whether afforded to the State or one of its representatives such as a Minister – usually with a narrowing effect. This can also be treated as an element of emerging best practice.

In EarthLife Africa, South Africa’s High Court was asked to determine whether the climate-related impacts of a new coal-fired power station needed to be taken into account before approval for the project was granted.⁷⁷ The Court acknowledged that the relevant legislation did not expressly refer to climate change. However, with reference to the Paris Agreement, the Court held that climate change was a ‘necessary and relevant’ consideration for the environmental review of the project, and that the failure to take it into account rendered the approval process for the project unlawful. The Court noted:

The respondents further argued that the power station project is consistent with South Africa’s NDC under the Paris Agreement, which envisages that South Africa’s emissions will peak between 2020 and 2025. Again I agree with EarthLife that this contention misses the point. The argument is not whether new coal-fired power stations are permitted under the Paris Agreement and the NDC. The narrow question is whether a climate change impact assessment is required before authorising new coal-fired power stations. A climate change impact assessment is necessary and relevant to ensuring that the proposed coal-fired power station fits South Africa’s peak, plateau and decline trajectory as outlined in the NDC and its commitment to build cleaner and more efficient than existing power stations.⁷⁸

The Canadian Supreme Court in Greenhouse Gas Pollution Pricing Act is similarly illustrative of the role that international law can play in interpreting statutory discretion.⁷⁹ The case concerned the constitutional validity of Canada’s Greenhouse Gas Pollution Pricing Act (GGPPA) in light of the division of power between the federal and provincial levels of government in Canada.⁸⁰ In considering the respective governments’ powers, the Court referred to the urgent need to reduce GHG emissions, Canada’s obligations under the UN climate treaty regime, and the reference to the Paris Agreement in the preamble of the GGPPA. This led the majority of the Court to find that climate change is a global challenge that cannot be left exclusively to the provinces to address. A carbon pricing backstop was an effective way for the Federal Government to ensure progress on its commitments under the Paris Agreement, while still leaving room for provinces to develop their own mitigation policies.

12.4 Replicability

Many aspects of how courts have engaged with international law in climate litigation to date are replicable in other jurisdictions, including the emerging best practices identified earlier. There are two key reasons for this. Firstly, the most relevant international treaties – the UNFCCC and the Paris Agreement – enjoy almost universal ratification, providing litigants and judges with a common source of norms in the context of climate litigation.⁸¹ Consequently, interpretations and applications of these instruments by courts in one jurisdiction may offer valuable guidance to courts in other jurisdictions, even in the absence of any formal binding effect. Secondly, the primary way in which international law has been invoked in the jurisprudence (i.e. indirectly) lends itself to replicability. This is because how and to what extent the applicable international law norm is formally incorporated into the national legal system is less relevant.

Each legal system has its own rules regarding the reception of international law which operate to regulate how courts engage with international law. However, as noted in Section 12.1.2, various rules and practices have the effect of blunting or moderating the rules that dictate whether a particular legal system is considered ‘monist’ or ‘dualist’. New Zealand, for example, is a dualist system – requiring international law to be translated into domestic law via legislation for it to become part of the domestic legal system. Still, the presumption of consistency applied by New Zealand courts favours an interpretation of statutory law that is consistent with international law where possible. This is similar to the ‘reflex effect’ described by the Dutch District Court in the Urgenda case, despite the Netherlands being a monist system. Writing extrajudicially, the current Chief Justice and two Judges of the Supreme Court of New Zealand noted that:

New Zealand courts apply a presumption to the interpretation of statutes that Parliament did not intend to legislate contrary to New Zealand’s international obligations. We anticipate that international treaties in the climate change area will increasingly be used in this way in litigation and it may be that courts will, as they respond to the magnitude of the issue, seek to strengthen the presumption.⁸²

There is therefore considerable scope – even accounting for how different legal systems receive international law – for courts to draw on how courts from other traditions have treated international law in climate litigation.

12.5 Conclusion

A survey of the relevant case law to date highlights the extent to which courts across diverse jurisdictions have drawn on international law in adjudicating climate cases. This is unsurprising given the inherently global nature of climate change. As explained by the Canadian Supreme Court in its decision in Greenhouse Gas Pollution Pricing Act regarding the unique features of climate change:

First, [climate change] has no boundaries; the entire country and entire world are experiencing and will continue to experience its effects. Second, the effects of climate change do not have a direct connection to the source of GHG emissions. Provinces and territories with low GHG emissions can experience effects of climate change that are grossly disproportionate to their individual contributions to Canada’s and the world’s total GHG emissions.…Third, no one province, territory or country can address the issue of climate change on its own. Addressing climate change requires collective national and international action. This is because the harmful effects of GHGs are, by their very nature, not confined by borders.⁸³

The most important conclusion to be drawn from the cases reviewed is that international law can significantly influence domestic law interpretation to help overcome obstacles litigants face when seeking recourse for climate change-related harms. The details will vary from jurisdiction to jurisdiction, but the trend is clear and important. Even non-binding sources of international law offer important context for helping to shape domestic law to fairly and effectively deal with climate cases. The legitimacy of legal systems depends on this, which serves to encourage courts to draw on international law in their deliberations and legal analysis.

The role of international courts and tribunals in addressing climate change is also receiving increasing attention. At the time of writing, the International Tribunal for the Law of the Sea,⁸⁴ the IACtHR,⁸⁵ and the International Court of Justice have each received requests seeking an advisory opinion seeking to clarify the obligations of States in light of the climate crisis.⁸⁶ Each opinion will serve as a critical opportunity for these international courts to build on the foundation established by national courts in emerging best practices. Clearly, courts at all levels have important roles to play in further clarifying and enforcing the obligations of States and non-State actors in the context of the climate crisis.

13 Common but Differentiated Responsibilities and Respective Capabilities

Patricia Galvao Ferreira *

13.1 Introduction

This chapter examines how domestic courts have considered the principle of ‘common but differentiated responsibilities and respective capabilities’ (CBDR-RC) when deciding lawsuits alleging violations of domestic statutory obligations, constitutional rights, or common law duties by governments in the context of efforts to mitigate climate change. Although CBDR-RC emerged first as a principle of international law to guide State-to-State relations (outward-looking), national courts are increasingly relying on CBDR-RC to help interpret the scope of national climate obligations (turning this principle ‘inward-looking’).¹

A growing number of courts are relying on CBDR-RC when analysing a country’s individual obligation to do their ‘fair share’ of global mitigation efforts under the United Nations (UN) climate regime or when defining the scope of each country’s unique due diligence standard of protection in the face of global climate risks. Courts are using CBDR-RC as part of a set of hard and soft international environmental law standards to help determine what level of political discretion governments have when deciding whether to reduce emissions in their territories, how much to reduce, and by what timeline.

It is worth noting that while some courts are more explicit in their application of the CBDR-RC principle, others are doing so implicitly, by engaging with related concepts such as a country’s obligation to do their part and contribute their ‘fair share’ of global climate efforts. This chapter therefore includes examination of decisions where courts explicitly referred to CBDR-RC as a relevant principle when setting the legal standards applicable to the adjudication, articulated reasonings related to the concepts of fair distribution of climate responsibilities, invoked CBDR-RC in the interpretation of specific legal obligations, or engaged with concepts directly related to the principle. Thus far, CBDR-RC has featured primarily in climate mitigation cases, particularly but not exclusively in lawsuits challenging the legality of overall efforts of a State to mitigate climate change.

Although the CBDR-RC jurisprudence is still nascent and at times inconsistent, it holds relevance due to the important role this principle plays in the effectiveness of the international climate change regime, and in worldwide efforts by those most affected by climate impacts to promote climate justice. As discussions on each country’s ‘fair share’ of global climate efforts pick up pace in the context of the 2015 Paris Climate Agreement’s (PA) iterative process of pledge and review of national contributions, aimed at closing the emissions gap to achieve the temperature goal of ‘well below 2°C’ and striving to remain at ‘1.5°C’, we expect the CBDR-RC jurisprudence to expand over time. There is an expectation that more judicial decisions will engage with the principle, following plaintiffs invoking CBDR-RC in complaints before international human rights bodies such as the Committee on the Rights of the Child (CRC), the Human Rights Committee (HRC), and the European Court of Human Rights. CBDR-RC also features in the upcoming Advisory Opinion (AO) by the Inter-American Court of Human Rights (IACtHR) on the scope of State obligations to respond to human rights implications of climate threats. With courts’ engagement with CBDR-RC becoming more established, it is also possible to predict that it will appear in future climate litigation related to climate finance, adaptation, or loss and damage.

In the balance of this chapter, Section 13.2 introduces a background discussion on two issues that are central to understanding how courts are finding legal content in the emerging concept of national ‘fair shares’ of global climate efforts: a) the evolution of the CBDR-RC principle in the international climate regime; and b) the scientifically backed international political consensus on the global average temperature goals needed to avoid dangerous climate impacts, as well as the associated concepts of remaining global carbon budgets and fair allocation of national carbon budgets. Section 13.3 then reviews the CBDR-RC case law development; Section 13.4 highlights emerging best practices; Section 13.5 analyses the potential for replicability; Section 13.6 concludes with a few observations.

13.2 Relevant Background Issues

13.2.1 CBDR-RC in International Climate Law

CBDR-RC is foundational to international environmental law² and is deeply embedded in the UN climate regime.³ The principle has two separate elements: the common responsibility of States to respond to the global climate change challenge; and the need to differentiate which ‘fair share’ of the common responsibility should be assigned to each individual country according to a series of possible equity benchmarks.⁴ These equity benchmarks have never been enumerated in the text of international climate law agreements. In climate negotiations and in decisions of the Conference of the Parties (COP) to the UN Framework Convention on Climate Change (UNFCCC), we find reference to the following criteria: individual responsibilities for the climate problem (e.g. historic or current greenhouse gas (GHG) emissions, absolute emissions, or per capita emissions); capabilities to take climate action (financial, technological, or institutional capacities); and/or stages of development.⁵

Climate action has been long recognised as a common responsibility of all countries. As an international problem of ‘common concern’, climate change can only be confronted via multilateral cooperation.⁶ As the Intergovernmental Panel on Climate Change (IPCC) noted in its 2014 Assessment Report 5 (AR5), international cooperation is crucial to address ‘global commons’ challenges such as climate change, characterised by having ‘multiple actors that are diverse in their perceptions of the costs and benefits of collective action; emissions sources that are unevenly distributed; heterogenous climate impacts that are uncertain and distant in space and time; and mitigation costs that vary’.⁷ States have consistently reaffirmed their common responsibility, including in the latest COP 27 decision in which they reiterated ‘the critical role of multilateralism … including in the context of the implementation of the Convention and the Paris Agreement, and the importance of international cooperation for addressing … climate change’.⁸

Although there is also consensus on the general need to differentiate each individual State’s ‘fair share’ of global climate efforts, the relative importance of the various possible equity benchmarks for differentiation, and on how exactly differentiation should be implemented in a world where contributions to GHG emissions, financial and technological capabilities, and development indicators are in flux, has remained under political dispute. The differentiation element of CBDR-RC can thus be considered an open standard of international climate law, a standard whose normative content is currently being defined by State practice, judicial interpretation, and continuous international negotiations.

Despite the lack of consensus on specific equity benchmarks, it is possible to identify a significant level of agreement over a set of normative expectations that have been at the core of differentiated responsibilities since the inception of the international climate regime. One normative expectation is that developed countries must ‘take the lead’ in the international climate response, and a second normative expectation is that differentiation must be guided by equity considerations.⁹ The allocation of differentiated climate responsibilities along a North–South (developed countries–developing countries) axis has been a constant element of CBDR-RC in the text of various climate legal agreements and decisions. The UNFCCC preambular language recognises that industrialised countries are the source of most past and current (in 1992) GHG emissions and should assume greater responsibility.¹⁰ Operative provisions of the UNFCCC also contain a directive that developed countries should ‘take the lead’ in combating climate change and its adverse effects.¹¹

The PA represents a new approach to international equity in the climate regime, replacing the top-down structure and binary Annex I/non-Annex I distinction of the Kyoto Protocol with a bottom-up, self-differentiation approach to the formulation of ‘Nationally Determined Contributions’ (NDCs). CBDR-RC remains, however, a fundamental principle, expressly appearing in the preamble and in provisions relating to the Agreement’s purpose, progression, and long-term low GHG emissions development strategies, besides various references in specific operative provisions, including on mitigation, finance, and adaptation.¹² Despite its significantly altered form, including the added expression ‘in light of different national circumstances’, the two basic normative expectations associated with CBDR-RC remain: developed countries must play a ‘leadership role’; and each NDC is expected to represent a country’s ‘fair share’ of global efforts according to their contributions and/or capabilities and national circumstances.¹³

In other words, the common aspect of CBDR-RC was thus strengthened, but the normative expectation of differentiation based on equity considerations remains, including a North–South distinction based on ‘leadership’ of developed countries. Without international consensus on which equity benchmarks should be considered (and given which weight) when defining individual ‘fair shares’, and on what exactly should the concept of ‘leadership’ of developed countries mean in practice, there are various parallel normative discussions on what constitutes each country’s ‘fair share’ taking place.¹⁴ In addition, discussions about the precise content of developed countries’ obligations with respect to finance and technology transfer are ongoing.¹⁵

The operationalisation of differentiation in Article 4 of the PA, on mitigation, is especially relevant to this chapter, as thus far all climate lawsuits invoking CBDR-RC relate to mitigation. In Article 4, Parties agreed to peak emissions as soon as possible and to undertake progressive and rapid emissions reductions in order to achieve net zero emissions by 2050.¹⁶ They have also agreed that emissions will take longer to peak in developing countries than in developed countries.¹⁷ The language indicates that Parties have certain leeway when defining the scope of their mitigation actions under their NDCs. This flexibility is, however, bounded by certain directives, including that: a) the sum of individual contributions must be sufficient to achieve the PA long-term temperature goals; b) each successive NDC ‘will represent a progression [over the preceding one] and reflect its highest possible ambition’; and c) the NDC will reflect the country’s ‘common but differentiated responsibilities and respective capabilities, in light of different national circumstances’.¹⁸

There is no mechanism to review the adequacy of each individual State’s contribution to the long-term goals, or the ‘fairness’ of these contributions. The PA relies instead on two main mechanisms. The first is an enhanced transparency framework whereby each country has the legal obligation to regularly report on their progress in contributing their share to meet the global goals.¹⁹ The second is the global stocktake, whereby Parties to the PA will periodically review the sum of reductions pledged in the NDCs to assess the collective progress towards the global temperature goals and to identify what added levels of effort are still needed.²⁰

The normative expectations that NDCs will reflect a country’s ‘fair share’ to the collective effort, based on differentiated responsibilities and capabilities in light of national circumstances, and that developed countries will continue to ‘take the lead’ are vital for building international trust in the PA iterative process. The 2018 Paris Rulebook requires countries to provide narrative justification for the ambition and fairness of their NDCs when regularly reviewing and updating them, including how they are addressing the normative expectations of developed country leadership, progression, and highest possible ambition.²¹ Despite the lack of international consensus on equity benchmarks, a country’s justification of how they arrived at their proposed ‘fair share’ can be – and has been – politically scrutinised by other countries and by non-State actors.²² And now domestic courts are also finding normative content on these international legal concepts of ‘common responsibility’ and ‘differentiated fair share’.

Before examining concrete examples of courts’ engagement with CBDR-RC, the chapter briefly reviews the scientifically backed political consensus (reflected in COP decisions and the Paris Agreement) on the need to keep the global average temperature between 1.5^oC and 2^oC, as well as calculations of the remaining global carbon budget based on this temperature goal, as they are key to understanding the use of CBDR-RC as an interpretive tool in climate litigation.

13.2.2 Long-term Temperature Goal and Carbon Budgets

Courts around the world have recognised the best available climate science assessed in IPCC reports as part of the undisputed factual basis informing their adjudication of climate lawsuits.²³ Virtually all climate decisions include reference to IPCC reports on the state of climate science to demonstrate, inter alia: estimates of global temperature levels that would avoid catastrophic impacts; and pathways for emissions reductions that would ensure the world keeps global temperature rise below agreed limits. The IPCC 1.5^oC Special Report and Assessment Report Six (AR6) have strengthened the scientific consensus (already reflected in the temperature goal of the Paris Agreement) on the risks of allowing global average temperatures to exceed 1.5^oC.²⁴

The concept of global carbon budgets has closely followed the consensus on maximum temperature goals based on climate science. A global carbon budget has been defined as ‘the maximum amount of cumulative global emissions to the atmosphere that may be “allowable”, based on the physical properties of the climate system, in order to stay below a politically agreed warming limit’.²⁵ Scientists have been able to estimate which maximum global carbon budgets will increase the likelihood of meeting the PA temperature goal. Carbon budgets featured prominently in IPCC AR4, IPCC Special 1.5^oC Report (SR5), and again in IPCC AR6.²⁶ The PA does not include a specific reference to carbon budgets. However, in the 2021 Glasgow Climate Pact, States expressed ‘alarm and utmost concern that … carbon budgets consistent with achieving the Paris Agreement temperature goals are now small and being rapidly depleted’,²⁷ while in the 2022 Sharm el-Sheikh Implementation Plan they affirmed their resolve to ‘pursue further efforts to limit the temperature increase to 1.5°C’.²⁸ The concept of carbon budgets has also been invoked in various policy debates, either to support specific policy proposals at the national level, to advocate for burden-sharing of climate efforts based on equity considerations, or to guide financial investments.²⁹ This policy uptake comes despite IPCC reports indicating residual scientific uncertainty about the size of remaining carbon budgets, depending on several factors.³⁰

The unsettled political debate on which equity markers should drive the distribution of shares of remaining global carbon budgets among countries makes it more challenging for the IPCC to estimate scenarios of specific remaining carbon budgets for each country or even groups of countries. Courts need to navigate this complex science-policy interface when trying to determine the existence and scope of domestic legal obligations in light of the normative framework of the international climate regime. The next section examines how courts are relying on CBDR-RC not to directly derive rights or legal duties but rather as an interpretive tool to help establish the scope of domestic legal obligations.

13.3 State of Affairs: Case Law Development

Citizen groups that are particularly vulnerable to climate impacts have increasingly invoked CBDR-RC across jurisdictions as part of their claims either that governments are setting emissions reductions targets that are too low in light of what should constitute their ‘fair share’ of global mitigation efforts, or that governments are failing to meet their obligations to effectively implement their legislated ‘fair share’ targets. These citizen groups argue that it is now possible to identify minimum legal standards of ‘fair share’ contributions for individual countries, based on the concept of a remaining global carbon budget in light of the PA temperature goal and other norms and principles of international climate law, particularly CBDR-RC. They argue that courts must therefore consider these minimum international legal standards when interpreting the scope of domestic constitutional, statutory, or common law legal obligations in the context of addressing climate risks.

13.3.1 Common Responsibility

A number of courts have now relied on the ‘common responsibility’ element of CBDR-RC – explicitly or implicitly – to help establish that States are under a legal obligation to do ‘their part’ to address the climate challenge. The starting points for courts when engaging with the common element of the CBDR-RC principle is the recognition of the significant risks and impacts posed by climate change, the global nature of the threat, and the inexorable need for a coordinated international response. In Urgenda,³¹ Grande-Synthe,³² Neubauer,³³ and Klimaatzaak,³⁴ the courts took judicial notice that the global dimension of climate change requires governments in each country to engage in a collective response through international cooperation, if they are to protect their citizens from the significant dangers of climate change. By reproducing relevant provisions of the UNFCCC and the PA, the Dutch, French, German, and Belgian courts either explicitly or implicitly recognise that by joining the international climate regime under the UNFCCC, governments acknowledge their common, albeit differentiated, responsibility over this global response.

Courts either explicitly reason³⁵ or infer that by joining an international regime that explicitly affirms the need for global cooperation, governments incur a legal obligation to fulfil their part of shared global efforts as part of their duty of care to protect citizens against significant climate risks and impacts. This is an important development in climate litigation. Courts are using the ‘common responsibility’ aspect of CBDR-RC to reject a prominent defence which governments have advanced against climate lawsuits over the years: that their nationally determined emissions reduction targets and other climate plans are not legally binding under international law or national law and, therefore, are discretionary political acts that should be exempt from judicial review. This is also an important development in international environmental law, as national courts are now expanding on a principle of international (State–State) cooperation to give it normative content when interpreting obligations owed to individuals.

This reasoning can be seen as distinct from and additional to the arguments used to reject another common defence advanced by governments (and corporations) against climate lawsuits: lack of causation or ‘de minimis’ / ‘drop in the ocean’ contributions.³⁶ The argument in the lack of causation defence is that governments and corporations have an obligation to do their part by reducing emissions under their control, no matter how small their share of contributions. This argument is anchored in the fact that climate change is caused by the combination of a myriad of sources that, even if insignificant in isolation, jointly become a significant problem.³⁷ Independent of what others are doing, a government or corporation can be found to have an obligation to act in order to minimise the danger by reducing emissions that they can control. This legal debate can be linked to concepts of causation in tort law and the need to identify relevant contributors to a collective legal wrong or problem.

The reasoning based on the ‘common responsibility’ element of CBDR-RC is different, as it places the focus not on causation or contribution but rather on remedy or redress. Distinct from the causation defence, the redressability defence in climate litigation relates to arguments that the creation and implementation of domestic climate policies are impervious to judicial review, as a judicial decision mandating a country to set a certain minimum level of GHG emissions, or to implement emissions reduction targets, will not be able to effectively redress plaintiffs’ harms or reduce their risks. Under this argument, due to the global nature of climate change, an effective remedy to plaintiffs’ injuries or risks depends on the uncertain or speculative response from various other governments and actors, something courts have no power to influence; in other words, it is a political rather than a legal question. This debate appeared in Massachusetts v EPA, where the US Supreme Court found the redressability requirement satisfied because the requested relief for EPA to regulate CO₂ emissions from American motor vehicles, even if not alone solving global climate change, would likely slow or reduce impacts or risks significantly.³⁸ In the case Juliana v United States, the Ninth Circuit panel declared the lawsuit non-justiciable in part because the requested injunction for the US to develop and implement a plan to do its part to reduce emissions would not solve global climate change. In other words, the case was dismissed on redressability grounds.³⁹

When using CBDR-RC to help interpret the scope of legal obligations, courts are taking judicial notice that each country has politically and legally agreed, by ratifying the UNFCCC and the PA, that they depend on the actions by the rest of the international community if they are to afford any level of protection to their citizens from the impacts and dangers of global climate change. Therefore, national courts in the Netherlands,⁴⁰ Germany,⁴¹ France,⁴² and Belgium⁴³ have concluded that since addressing climate risks is a common responsibility of all States, there is at least a normative command, if not a legal obligation, for each country to do their part, by contributing their ‘fair share’ to the multilateral efforts on climate change, as the only way to offer a measure of effective redress.

Courts are recognising that even those countries that contribute minimal emissions are equally (or often disproportionately more) vulnerable to climate impacts. These countries are highly dependent on the success of the international response to protect their citizens. Governments cannot argue that there is no legal obligation to do their part of the common response, because it will not offer sufficient or effective redress for a problem that is global and collective, when their lack of action is actively undermining global efforts and essentially making any potential measure of redress more difficult or impossible.

13.3.2 Differentiated Responsibilities and Capabilities

The second way in which courts are engaging with CBDR-RC relates to the ‘differentiated’ aspect of the principle, which more directly relates to the ‘fair share’ concept. Various plaintiffs have challenged the legality of current emissions targets set by States for being too low to represent their ‘fair share’ of global efforts and therefore inadequate to offer an effective contribution to the global response to the dangers of climate change.⁴⁴ When courts engage with the concept of a country’s minimum ‘fair share’ they are again considering that countries have politically agreed to the PA temperature goal and often legalised this goal by referencing it in national climate law. Courts are also noting that a global target temperature goal allows for scientific calculations of remaining global carbon budgets with limited or no overshoot, even when lingering scientific uncertainties make exact calculations of this budget elusive.⁴⁵

Courts address the normative expectation that a country’s individual ‘part’ must represent its ‘fair share’ of global efforts when they engage with the range of equity benchmarks articulated in the effort-sharing negotiations and principles of the climate regime or in the literature. For example, various courts have taken judicial notice of a country’s contributions to global emissions in absolute or per capita terms or of its levels of socio-economic development achieved in part due to historic emissions.⁴⁶ As part of their exercise to decide whether the ‘differentiated’ element of CBDR-RC carries legal meaning, a small number of courts have also engaged with the normative expectation that developed countries should ‘take the lead’ in global climate efforts, when identifying what would be a legal minimum ‘fair share’ of the remaining global carbon budget for each individual country.⁴⁷

Enduring disputes among countries over how to translate the differentiated element of CBDR-RC into concrete effort-sharing standards in the international climate regime, and the Paris Agreement bottom-up model of self-differentiation via NDCs, have left courts struggling to identify a core normative content from the evolving CBDR-RC principle.⁴⁸ Courts are arriving at different conclusions as to what extent the CBDR-RC principle has or has not curtailed the level of discretion of legislative and administrative bodies to set their own mitigation targets, or to meet these targets, based on the concepts of ‘fair share’, differentiation, and ‘leadership role’ for developed countries. Some courts, like in the cases of Grande-Synthe,⁴⁹ Notre Affaire à Tous,⁵⁰ and Klimaatzaak,⁵¹ make references to CBDR-RC in their decisions in the context of discussing countries’ ‘fair shares’, yet they do not articulate whether (and how) they considered the different CBDR-RC equity benchmarks when interpreting the scope of national climate obligations. These courts merely assert that the Paris Agreement left it to each individual country to propose their individual ‘fair share’ contributions to the international climate response.

In Urgenda and Neubauer, the courts also relied on the CBDR-RC principle (explicitly or implicitly) to grapple with the question of the degree of discretion governments have in determining their individual ‘fair share’ of global efforts to address climate change. These courts found that although there is no legal standard determining the exact scope of individual emissions reductions targets or timelines, they could assess whether the State has adopted the minimum reasonable measures to fulfil their duty of care to protect against the dangers of global climate change, based on existing international climate law principles and standards, including CBDR-RC, but also cooperation, the precautionary principle, and intergenerational equity. A more detailed examination of the courts’ reasoning is included in the next section.

As part of this discussion, the Dutch courts have considered whether the CBDR-RC directive that developed countries play a leadership role in global climate efforts has normative value when determining the degree of discretion States hold when defining their minimum ‘fair share’. The Hague Court took notice that by agreeing, under international climate law, to take the lead in climate action with other developed countries, the Netherlands has ‘therefore committed to a more than proportional contribution to reduction, in view of a fair distribution between industrialized and developing countries’.⁵² The discretionary power of the State to decide its ‘fair share’ was thus limited by the legal norms and principles of the international climate regime, including CBDR-RC.

The implication is that the political discretion of the Dutch government to choose among the broad array of equity benchmarks when defining its ‘fair share’ for the Netherlands is not unlimited. The Dutch courts are indicating, if implicitly, that as a developed country that needs to do a more than proportional contribution to reductions, the Netherlands is entitled to a smaller piece of the remaining global carbon budget than if calculated based on global emissions per capita (GEC). In contrast, the German courts in Neubauer⁵³ and German Family Farmers⁵⁴ found that the German government still keeps the wide political discretion to choose among equity benchmarks when defining a ‘fair share’, including by choosing to use the GEC benchmark, therefore apparently dismissing a normative role for the concept of developed countries’ leadership role under the CBDR-RC principle.⁵⁵

Judicial engagement with the CBDR-RC element of ‘leadership role’ for developed countries has begun to spread outside European jurisdictions. The New South Wales Court in Gloucester Resources Limited v Minister for Planning⁵⁶ invoked this concept when rejecting the market substitution argument advanced by the mining company against the denial of their permit to expand a coal operation due to increased carbon emissions, namely that developing countries with weaker regulations would fill the gap in coal production if Australia left coal on the ground.⁵⁷ The Philippines Human Rights Commission also addressed the ‘leadership role’ of developed countries in their Carbon Majors report. The Commission found that although all States have the responsibility to contribute to the response to climate change, whether they have contributed no GHG emissions or half of current emissions, highly industrialised countries that have benefited from historic emissions ‘bear a larger share in providing solutions to the problems they have created’.⁵⁸

The matter has also recently been addressed at the international level in the recent General Comment issued by the CRC. The Committee establishes a strong link between climate inaction and human rights violations and elaborates on what this means in terms of mitigation. It calls ‘for urgent collective action by all States to mitigate greenhouse gas emissions, in line with their human rights obligations’, noting that ‘historical and current major emitters should take the lead in mitigation efforts’.⁵⁹ It further specifies:

When determining the appropriateness of their mitigation measures in accordance with the Convention, and also mindful of the need to prevent and address any potential adverse effects of those measures, States should take into account the following criteria:

1. (a) Mitigation objectives and measures should clearly indicate how they respect, protect and fulfil children’s rights under the Convention. …

2. (b) States have an individual responsibility to mitigate climate change in order to fulfil their obligations under the Convention and international environmental law, including the commitment contained in the Paris Agreement to hold the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels by 2030. Mitigation measures should reflect each State party’s fair share of the global effort to mitigate climate change, in the light of the total reductions necessary to protect against continuing and worsening violations of children’s rights. Each State, and all States working together, should continuously strengthen climate commitments in line with the highest possible ambition and their common but differentiated responsibilities and respective capacities. High-income States should continue to take the lead by undertaking economy-wide absolute emission reduction targets, and all States should enhance their mitigation measures in the light of their different national circumstances in a manner that protects children’s rights to the maximum possible extent.⁶⁰

13.4 Emerging Best Practices

In the context of a yet fledgling jurisprudence on CBDR-RC, many courts are still struggling to navigate the complexity of this multifaceted and evolving principle. It is, however, possible to identify a few examples of emerging best practices (EBPs). Since plaintiffs will most likely continue to invoke CBDR-RC in climate litigation, this section highlights some EBPs, while also discussing some missteps that courts can avoid when called to examine the normative value of CBDR-RC as an interpretive tool to delimit the scope of obligations or rights in the context of foreseeable climate risks and impacts.

The German Constitutional Court offered the most comprehensive treatment of the legal consequences of the ‘common responsibility’ element of CBDR-RC in Neubauer, if implicitly. After referencing CBDR-RC in the Paris Agreement as part of the relevant international law framework it was taking into consideration,⁶¹ the Court declared that the global nature of climate change does not invalidate the national obligation to take climate action, instead being ‘significant for determining the content of the duty of climate change related protection’ under German Constitutional law.⁶² The Constitutional Court held that the global nature of climate change compels the State to engage in internationally oriented activities to tackle climate change, requiring it to promote climate action within the international framework.⁶³ According to the Court, the State is under a constitutional obligation to take steps to protect citizens against climate risks, ‘with the help of international involvement’.⁶⁴

The German Court went on to say that the international engagement aspect of the constitutional obligation includes two distinct elements. First, international engagement requires negotiation and participation in international agreements to promote the collective international action needed to offer effective protection to German citizens. Second, international engagement requires effectively implementing individual contributions agreed to in the international climate regime. In the Constitutional Court’s words, ‘the international dimension of the obligation to take climate action [under the German Constitution] is not confined to the task of seeking to resolve the climate problem at the international level and ideally reaching some agreement to that effect. Rather, the constitutional obligation to take climate action also extends to the implementation of agreed solutions.’⁶⁵ It is reasonable to affirm that the Constitutional Court has thus set one obligation of conduct (to negotiate and to participate in good faith in international agreements to deliver a global response to climate change) and one obligation of results (to effectively implement whatever contribution it has agreed to at international level, to avoid undermining the success of the collective efforts). This was the first time that a national court made this linkage, that as part of their ‘common responsibility’ to address global climate change through international cooperative efforts, a State is under an obligation to implement their NDCs once they are defined and set in national law.

To be clear, the Constitutional Court did not explicitly articulate that it was using CBDR-RC to help interpret this obligation to participate in the elaboration and to implement international obligations. The ‘common responsibility’ element of CBDR-RC, however, is the one that manifests the scientifically backed international political consensus that climate change is an environmental problem of ‘common concern’ that evades unilateral or plurilateral action, necessarily requiring a multilateral or global coordinated response.

Unlike the traditional outward treatment of the principle of cooperation under international environmental law, which sets State-to-State obligations to cooperate to respond to problems of ‘common concern’ (in order to prevent or address transboundary harm to each other), here the Court is applying the ‘common responsibility’ element of CBDR-RC inward: to help interpret the scope of constitutional obligations of protection for German citizens against the risks of climate change, which require international coordination. To protect German citizens, the government must participate in good faith in the international regime by doing its part of the global response, which should represent the country’s ‘fair share’ to keep the legitimacy and trust of the collective response. This is an EBP because it addresses the problematic State defence accepted by some courts that, because climate action in one country cannot redress the risks or impacts of climate change, climate obligations are non-justiciable or defy judicial responses.

It is worth noting that the Constitutional Court was careful not to overstep the division of powers, refraining from deciding on the precise scope of an obligation to participate in good faith in the international climate legal regime.⁶⁶ It set instead minimum standards [very low, critics may say] affirming that a violation of a duty of protection occurs ‘if no precautionary measures whatsoever have been taken, or if the adopted provisions and measures prove to be manifestly unsuitable or completely inadequate for achieving the required protection goal, or if the provisions and measures fall significantly short of the protection goal’.⁶⁷ The Court concluded that by ratifying the PA and adopting its temperature limits under German law, the legislator had set the country in a direction that ‘gives the German state an opportunity to effectively fulfil its constitutional mandate to take climate action through its own efforts embedded within an international framework’.⁶⁸ The Court concluded that the State was not in violation of this obligation at the time. Despite this low standard, the logical conclusion is that the German Constitutional Court established that the State does not have the unlimited discretion to withdraw from international cooperative regimes, or to arbitrarily decide on its own climate actions, thereby ignoring the international regime’s principles and standards.

In other words, the German Court granted the legislator significant leeway when deciding the allocation of global mitigation efforts that represents Germany’s ‘fair share’. However, as discussed later, it affirmed that the necessity to engage internationally generates an obligation for the State to participate in the international legal regime in good faith, by both considering relevant international climate law principles (including differentiated responsibilities and capabilities) when determining these national targets, and effectively implementing these nationally determined targets in order to build trust, as mutual trust is key to the success of international climate efforts.

The Dutch Court decisions in the Urgenda case best illustrate how courts can engage with the various elements of the CBDR-RC: the common responsibilities element⁶⁹ as well as the two angles of differentiated responsibilities and respective capabilities, in light of national circumstances (leadership role for developed countries and self-differentiation based on equity benchmarks). The Dutch Court decisions represent EBP when clearly articulating the potential normative value of the ‘leadership role’ of developed countries under the CBDR-RC principle. As the ‘leadership role’ of developed countries is an important element of CBDR-RC and is fundamental to maintain trust in international cooperative efforts to address climate change, it is essential that courts in developed countries tackle this normative concept when analysing the scope of legal obligations to contribute their ‘fair share’.

The Urgenda decisions found that this leadership role requires developed countries to contribute a ‘more than proportionate share’ of global mitigation efforts.⁷⁰ The evident conclusion, although not stated with these exact words by the Dutch courts, is that the ‘leadership role’ element of CBDR-RC constrains the political discretion of developed countries to define their ‘fair share’ exclusively based on options such as ‘emissions per capita rights’ (EPC).⁷¹ EPC approaches to determining a ‘fair share’ of the remaining global carbon budget take the status quo of highly unequal past levels of emissions, and other equity benchmarks such as financial and technological capacity or socio-economic development needs, for granted. The Dutch courts did not identify a specific equity formula that governments were legally required to use to define ‘fair share’, recognising that there is not yet a political consensus on equitable allocation formula enshrined in international or Dutch law. Although governments retain political discretion to define specific fair shares based on ethical assumptions and political choices, they have to be consistent with the principles and norms of the UNFCCC and Paris Agreement. Current research broadly acknowledges that EPC and grandfathering approaches do not distribute global efforts in a fair manner, according to CBDR-RC, rather benefiting countries with a comparably current high share of emissions and placing developing countries at disadvantage.⁷²

The Dutch courts in Urgenda also offer the most comprehensive discussion of CBDR-RC equity benchmarks, when deciding whether there is a duty of care to contribute a minimum fair share.⁷³ First, the courts explicitly deliberate on the Netherlands’ differentiated responsibility based on its contributions to GHG atmospheric concentration. For example, the District Court (first instance) discussed the country’s absolute and per capita emissions in comparison with other developed countries (particularly EU and the USA) but also the BRIC emerging economies (Brazil, Russia, India, and China).⁷⁴ The District Court explicitly states that developed countries accepted to take the lead in global climate efforts because ‘[f]rom a historical perspective the current industrialized countries are the main causers of the current high greenhouse gas concentration in the atmosphere and that these countries also benefit from the use of fossil fuels, in the form of economic growth and prosperity’.⁷⁵ Besides historic contributions, the District Court also considered the capabilities equity indicator by stating that this prosperity also means that ‘[developed] countries have the most means available to take measures to combat climate change’.⁷⁶

The Dutch Court of Appeal (second instance) equally considered contributions (responsibilities) and capabilities as relevant in the context of the leadership role: ‘taking into account their per capita emissions, the long history of their emissions and their resource bases, the Annex I countries must take the lead in fighting climate change’.⁷⁷ The Court of Appeal went on to consider that the Netherlands has relatively high per capita emissions, even when compared to other developed countries. In absolute emissions, the Court noted that the Netherlands ranks 34th out of 208 countries and ‘of the 33 countries with even higher emissions, only nine have a higher per capita emission and not a single one is an EU Member State’.⁷⁸ The district courts returned to responsibilities and capabilities indicators when rejecting the State’s defence that the timeframe to comply with the decision is too short, noting not only that the State has officially acknowledged the severity of the climate crisis but that:

It deserves further attention that the Netherlands as a highly developed country has profited from fossil fuels for a long time and still ranks among the countries with the highest per capita greenhouse gas emissions in the world. It is partly for this reason that the state should assume its responsibility, a sentiment that was also expressed in the UNFCCC and the PA.⁷⁹

The Dutch Supreme Court (apex decision) confirmed the lower courts’ decisions, stating that although the distribution of global efforts should not be based solely on historic emissions, they must be taken into consideration alongside capabilities.⁸⁰ Rejecting the argument that the IPCC AR4 emissions reduction range of 25–40 per cent was calculated for developed countries as a group, and should not be used to determine the Netherlands individual contribution, the Supreme Court reiterated that considering Dutch high per capita emissions and capabilities even when compared to other developed countries, ‘it would not be obvious for a lower reduction rate to apply to the Netherlands…’⁸¹ Although the Supreme Court concluded that the exact ‘fair share’ was still to be determined by political bodies, it made clear that they are bound by the set of equity benchmarks from the international climate regime when making this determination, shifting the burden to the State to justify why a lower reduction rate would apply to the Netherlands in light of equity benchmarks or other international climate law norms. This is in line with the interpretation the CRC made on the scope of developed countries’ ‘fair share’ obligations in their General Comment 26, as reproduced in Section 13.3.

The German Constitutional Court also showed best practice when articulating that the government is required to formulate its individual national contribution to global efforts in a way that will build trust among members of the collective response. Although not stated explicitly in the Neubauer decision, this articulation has two important normative implications that other courts can equally recognise. First, although governments retain leeway when deciding what constitutes their individual ‘fair share’, in the absence of clear international agreement on valid fairness benchmarks, they must justify how their calculation aligns with the principles and standards of the UN climate regime, particularly CBDR-RC. Shifting the burden to the State to justify the ‘fairness’ of their proposed contribution to global efforts to address climate risks and impacts is an EBP for minimum legal standards that courts can replicate. As noted in the IPCC AR6, the Paris Rulebook obliges Parties to provide information on fairness considerations in their NDCs, including reflecting equitable principles of the climate regime (CBDR-RC being a key principle).⁸²

The Dutch courts also showed EBP when they separated the ‘leadership role’ for developed countries from considerations of the set of CBDR-RC equity benchmarks that should guide governments in determining their ‘fair share’, even if the differentiated elements of CBDR-RC are interrelated (with the Dutch courts explicitly linking the ‘leadership role’ normative expectation to historic emissions, per capita emissions, and capabilities). CBDR-RC is likely to appear in future climate litigation in developing countries, including in high emitting emerging economies. Courts in the Global South will thus be urged to consider the normative role of the various equity benchmarks related to the principle in international climate law to determine the respective differentiated fair share, without engaging with the ‘leadership role’ exclusive to developed countries. It is important to clarify that the differentiated element of the CBDR-RC principle applies to the determination of responsibilities in all Parties to the UNFCCC, not only to developed countries.

By signalling that there is a distinct normative role for the CBDR-RC equity benchmarks for identifying minimum fair shares, the Urgenda decisions help to repel the mistaken view that CBDR-RC serves only to establish greater obligations to developed countries, with developing countries getting from the principle only a right to receive support for their climate action. Another mistaken view that the separate judicial treatment of the various elements of CBDR-RC, including the ‘common responsibility’ and the equity benchmarks, can help dispel is the one that proposes that the principle allows developing countries to concentrate only on climate adaptation rather than mitigation. As part of their common responsibility to pursue the temperature goal of the PA, all countries must propose their differentiated nationally determined contribution to emissions reductions. All countries must therefore do their part, however small, and justify why their NDC represents their ‘fair share’ of global efforts according to disclosed equity benchmarks.

Although not explicitly articulating it as a legal consequence of the CBDR-RC principle, the German Constitutional Court in Neubauer illustrates EBP in engaging with the ‘common responsibilities’ aspect of CBDR-RC, related to the global nature of the climate challenge. The Constitutional Court indicates that a blatant refusal to participate in global cooperative climate efforts to tackle climate dangers, or a patently inadequate contribution to such efforts, constitutes a constitutional violation. Other courts can now follow this best practice if their governments and parliaments decide, for example, to withdraw from the Paris Agreement without offering valid alternatives for global climate action.

13.5 Replicability

As the jurisprudence on CBDR-RC is still recent, there are questions related to its replicability. A flurry of pending cases in which CBDR-RC was either part of the plaintiffs’ claims or where related concepts of ‘fair shares’ and equity in light of international climate law have been considered indicates that it is very likely that other courts will engage with the principle in their reasoning. CBDR-RC plays a noticeable role in recent climate proceedings launched against Italy and Poland. In A Sud et al v Italy,⁸³ the plaintiffs argue that Italy’s proposed emissions reduction targets do not represent its ‘fair share’ based on a report prepared by Climate Analytics which ‘assesses the contribution of the Italian State towards meeting the Paris Agreement’s long-term temperature goal, in line with the principles of equity and common but differentiated responsibilities as enshrined in that agreement, so that its climate commitments represent a “fair share” towards achieving that goal’. Polish citizens, with support from the NGO ClientEarth, also relied on a Climate Analytics report on fair shares when they brought forward five similar cases questioning Poland’s decisions to allow GHG emissions in excess of their fair share.⁸⁴

Despite most of the decisions featuring CBDR-RC or related concepts of ‘fair share’ in light of international climate law equity principles and norms being concentrated in European jurisdictions, the principle or related concepts appear in courts’ reasonings in cases in Australia⁸⁵ and Canada.⁸⁶ In Do-Hyun Kim et al v South Korea,⁸⁷ which is still pending, a group of youth activists filed a complaint before South Korea’s Constitutional Court challenging the central government for their ‘inadequate’ climate policies. Although the plaintiffs did not explicitly invoke CBDR-RC, they engaged with related concepts of carbon budget and fair shares.

While all the cases reviewed in this chapter were presented before courts in developed countries, courts in the Global South will most likely be called to deliberate on the normative content of both the common element of CBDR-RC, and the equity benchmarks of responsibilities and capabilities. Plaintiffs in the Global South can use CBDR-RC arguments to challenge the legality of either timid targets or the failure to meet targets, based on each individual country’s obligation to contribute their ‘fair share’ to meet the temperature goal of the PA.⁸⁸

CBDR-RC has also been invoked in pending individual complaints related to climate rights before international bodies such as the CRC and the HRC and in the cases against Austria and Switzerland currently pending at the European Court of Human Rights.⁸⁹ The principle also appears prominently in the Portuguese children’s case against thirty-three European States (Duarte Agostinho v Portugal et al) before the European Court of Human Rights.⁹⁰ In Duarte Agostinho, the youth plaintiffs invoke CBDR-RC as part of the international legal framework to help challenge the emissions reduction targets from key European countries for not representing their ‘fair share’ of global efforts. In anticipation of arguments that, because there is currently no international agreement on a set of equity criteria to guide fair allocation of a remaining carbon budget, definition of a ‘fair share’ remains a political question and therefore impervious to judicial review, they argue that ‘fair share’ ambiguity should be resolved in their favour since this ambiguity ‘is a direct consequence of the failure by states (globally) to agree a clearly defined approach to sharing the burden of mitigating climate change’.

In January 2023, Chile and Colombia included five questions related to common but differentiated responsibilities as part of their request for an AO by the IACtHR⁹¹ which was called to clarify the scope of State obligations to respond to human rights implications of climate threats. This AO may generate new insights on how courts throughout Latin America will engage with CBDR-RC in climate litigation in the near future. Considering the evolution of the CBDR-RC principle in the PA, moving towards a more nuanced differentiation, we expect that plaintiffs from countries in different stages of development, but particularly from emerging economies with growing emissions, to engage with this principle in their climate litigation strategies.

Although all CBDR-RC cases have thus far been in civil law jurisdictions, there is no apparent obstacle for courts in common law countries to examine the normative value of CBDR-RC as an interpretive tool to help establish and define the scope of open common law concepts, or of statutory law in common law jurisdictions. Because courts are clear that they are using CBDR-RC as interpretive tools to help establish the content of open standards based on national law (rather than international legal obligations that may potentially generate rights), the jurisprudence discussed in this chapter can be replicated in countries that adopt a monist model or a dualist model of international law incorporation into national law.

Thus far, litigation invoking CBDR-RC has been restricted to cases related to climate mitigation. Yet the principle is also very relevant to questions related to international climate finance. It is fair to anticipate, for example, cases arguing that developed countries have a constitutional or duty of care obligation to provide a ‘fair share’ of climate finance to developing countries as part of their common but differentiated responsibility to effectively contribute to international climate efforts in a way that builds trust among other countries. Since developed countries as a group have an obligation to provide climate finance to developing countries under the UN climate regime, it is possible that similar arguments related to whether individual developed countries are contributing their ‘fair share’ of this collective financial obligation be raised in national or international courts. With the evolution of CBDR-RC from an outward-looking principle of international law (State-to-State) to an inward-looking principle (influencing the scope of obligations within jurisdictions), we should expect other innovative litigation strategies related to climate adaptation and loss and damage. Courts around the world should thus be prepared to properly address CBDR-RC arguments in the future.

13.6 Conclusion

The 2022 IPCC Sixth Assessment Report states with ‘high confidence’ that ‘issues of equity remain of central importance in the UN climate regime, notwithstanding shifts in the operationalization of [CBDR-RC] from Kyoto to Paris’.⁹² Yet, the same IPCC report has also recognised the challenge of determining ‘fair shares’ in a system based on voluntary, self-determined contributions and noted the low political feasibility of States agreeing on equity benchmarks within the UNFCCC regime at the moment.⁹³ As a result, actors and mechanisms outside the UNFCCC regime will continue to shoulder the burden of developing such equity benchmarks, as ‘it is only in relation to such a “fair share” that the adequacy of a state’s contribution can be assessed in the context of a global collective action problem’.⁹⁴

In this context, courts will undoubtedly feature among the actors increasingly facing questions related to fair effort-sharing in light of CBDR-RC in the context of climate litigation. The momentum of ‘fair share’ climate litigation shall pick up pace as Parties provide their narrative justification for the ambition and fairness of their NDCs, as required by the Paris Rulebook, as they are pressured to provide more rigorous information on their adopted equity considerations, and as the scientific community continues to work on reducing uncertainties over the remaining global carbon budget.

Furthermore, as the impacts and dangers of climate change become more evident, and questions on who should bear the costs of dealing with such impacts and risks become more prominent, plaintiffs will likely prompt courts to deliberate on the normative content of CBDR-RC when interpreting the scope of a country’s obligation to contribute its ‘fair share’ under the international climate regime in relation to adaptation, loss and damage, and finance, besides mitigation. This chapter offers some thoughts to inform what promises to be thriving legal debates in courts around the world in the years to come.

14 Intergenerational Equity

Sam Bookman and Margaretha Wewerinke-Singh *

14.1 Introduction

Intergenerational equity is a legal principle reflected in international treaties¹ and soft law instruments,² and recognised by many international and domestic tribunals.³ It encapsulates the idea that ‘[t]he present residents of the earth hold the earth in trust for future generations and at the same time the present generation is entitled to reap benefits from it’.⁴ Thus, the principle demands a just balance between the needs of present and future generations. Like other equitable principles, intergenerational equity reflects the need for flexibility and fairness. In the context of climate change, it demands consideration of justice: decisionmakers must pay attention to the distributive consequences of climate harms, government policies, and lack of action.⁵ Further, as the High Court of South Africa put it, intergenerational justice in the context of climate change involves ‘a rejection of short-termism as it requires the state to consider the long-term impact of pollution on future generations’.⁶ As a principle, intergenerational equity is rarely a standalone basis for decision-making. Rather, it informs the interpretation and application of legal doctrine, with implications for many areas of climate law. This includes issues discussed elsewhere in this volume, such as standing, admissibility, public trust,⁷ and the precautionary principle. Judges already frequently refer to ‘intergenerational equity’,⁸ ‘intergenerational responsibility’,⁹ ‘intergenerational justice’,¹⁰ or the broad interests of ‘future generations’¹¹ when considering the obligations owed by States and other actors. While terminology and doctrine may be jurisdiction-specific, the general animating principle – of considering the future interests of children and unborn generations – has travelled widely across borders.

Intergenerational equity is especially important in the context of climate change. As the UN Committee on the Rights of the Child (CRC) has observed, children are impacted by climate change more than adults in the ‘manner in which they experience such effects as well as the potential of climate change to affect them throughout their lifetime’.¹² This reflects two related dynamics. The first is future oriented. Climate change distributes benefits and burdens unequally over time: the failure by existing adults to mitigate greenhouse gas emissions and invest in adaptation infrastructure means that current children and future generations will experience greater harms.

The second dynamic relates to present, existing harms to children and young people. The dangers of climate change are not an abstract future proposition – they are already felt globally. As the Intergovernmental Panel on Climate Change (IPCC) has recognised, children are at particularly high risk of harm from the physical consequences of climate change (such as food and water security),¹³ as well as mental health impacts such as anxiety and stress.¹⁴ Furthermore, children and young people are rendered more vulnerable by their lack of political power – in particular, their inability to vote. Young people have highlighted these dynamics in cases across several jurisdictions, including Australia,¹⁵ the Philippines,¹⁶ Germany,¹⁷ Nepal,¹⁸ Colombia,¹⁹ and the United States.²⁰

The ongoing significance of intergenerational equity in climate litigation is evident in international and regional litigation. In the forthcoming case before the European Court of Human Rights (ECtHR), Duarte Aghostinho and others v Portugal and 32 other States, six Portuguese children have brought thirty-three member States of the Council of Europe before the ECtHR for alleged violations of Articles 2, 8, and 14 of the European Convention for the Protection of Human Rights and Fundamental Freedoms (ECHR) due to failure to take sufficiently ambitious climate action. In their claim, the applicants rely on intergenerational equity as a principle that must inform the interpretation of States’ obligations under the ECHR. The ECtHR recognised the importance of intergenerational equity in this claim by including a question on intergenerational equity in their invitation to the respondent States to react to the application: it asked whether ‘the defendant States [have] performed the obligations incumbent upon them …, read in the light of the pertinent provisions and principles, such as the principles of precaution and intergenerational equity, contained in international environmental law, including in the international treaties to which they are a Party’.²¹ Furthermore, the recent advisory opinion submitted to the International Court of Justice by the United Nations General Assembly calls on that court to provide guidance concerning obligations owed to future generations, a question which will undoubtedly require consideration and enumeration of intergenerational equity.²²

Against this backdrop, this chapter contributes to the debate on intergenerational equity and climate change. Like the other chapters in this Handbook, it is divided into a descriptive section and a normative section that identifies emerging best practice. In the first, descriptive section, we analyse how the principle of intergenerational equity has been applied in judicial decisions on climate change, specifically in decisions on cases initiated by children and youth. We survey three broad areas of jurisprudence: normative obligations owed by States; procedural mechanisms to ensure courtroom participation of children, young people, and representatives of future generations; and future-focused judicial remedies. These themes are often contained in one and the same judgment. By organising the section thematically, we create an overview of the state of play of climate change jurisprudence in connection with each of these themes across jurisdictions.

The second, normative part of the chapter pulls out judicial practice that could serve as a source of inspiration for legal reasoning in future cases. We consider such practices to be those which best give legal effect to the principle of intergenerational equity, or that best allow for judicial consideration of the principle in a courtroom setting. Continuing rapid emissions of greenhouse gases and failure to invest in climate adaptation infrastructure constitutes an injustice to future generations perpetrated by (some members of) the present. Normatively, only ambitious and equitable climate mitigation and adaptation policies and measures can be consistent with intergenerational equity.²³

Zooming in on the existing case law, we then identify six areas of emerging best practice. First, best practice entails recognising that based on intergenerational equity, States owe obligations to children, young people, and future generations, such as the development of mitigation and adaptation plans and targets which distribute obligations fairly within and across generations.²⁴ Second, emerging best practice includes cases where judges have ensured that decisionmakers must account for intergenerational equity in planning and consent decisions which may have negative long-term climate impacts or downstream consequences.²⁵ Another substantive emerging best practice is the recognition of children, young people, and future generations as classes which may experience discrimination because of insufficiently ambitious climate policy.²⁶ Furthermore, intergenerational equity considerations are dependent on effective representation in court. Emerging best practice recognises the importance of children’s participation both as representative of future generations (understood, as per the High Court of South Africa, as ‘a broad concept which can mean posterity, or those whose birth is imminent’)²⁷ and as vulnerable parties in the here and now. Ensuring such participation requires an open approach to issues such as standing, separation of powers, and certification of class actions. It may also require procedural innovations to facilitate courtroom participation and communicate judicial decisions.²⁸ Finally, emerging best practice incorporates the principle of intergenerational equity in crafting remedies that ensure long-term oversight and enforcement of judicial decisions.²⁹

14.2 Case Law Developments

14.2.1 Development of the Principle in International Law

Intergenerational equity forms part of the basis of international environmental law (IEL). The Stockholm Declaration of 1972 – widely recognised as one of IEL’s founding documents – observes that humans bear ‘a solemn responsibility to protect and improve the environment for present and future generations’.³⁰ Similarly, the United Nations Framework Convention on Climate Change (UNFCCC) requires States to ‘protect the climate system for the benefit of present and future generations, on the basis of equity and in accordance with their common but differentiated responsibilities and respective capabilities’.³¹ The principle of intergenerational equity has been extensively developed by the scholar Edith Brown Weiss, who argued that these (and other) statements of international law give rise to three obligations on States: to conserve options (ensuring future generations have a resource base they can use to ‘satisfy their own values’); to conserve quality (‘ensuring the quality of the environment on balance is comparable between generations’); and to conserve access (meaning ‘non-discriminatory access among generations to the Earth and its resources’).³² The interests of future generations are also reflected in the principle of sustainable development. Principle 3 of the 1992 Rio Declaration on Environment and Development – a non-binding but highly influential international law instrument – provides that ‘[t]he right to development must be fulfilled so as to equitably meet developmental and environmental needs of present and future generations’.³³

The most recent definition of intergenerational equity by a major international tribunal was recently provided by the UN CRC in its General Comment 26. In that Comment – and drawing on extensive consultation with children – the Committee noted that ‘children constantly arriving are also entitled to the realization of their human rights to the maximum extent’, and that ‘States bear the responsibility for foreseeable environment-related threats arising as a result of their acts or omissions now, the full implications of which may not manifest for years or even decades’.³⁴

Intergenerational equity has been developed and recognised by judges of the International Court of Justice (ICJ). In its 1996 Advisory Opinion on the Legality of the Threat or Use of Nuclear Weapons, the ICJ observed that

the environment is not an abstraction, but represents the living space, the quality of life and the very health of human beings, including generations unborn. The existence of the general obligation of States to ensure that activities within their jurisdiction and control respect the environment of other States or of areas beyond control is now part of the corpus of international law relating to the environment.³⁵

Separate and dissenting ICJ judges have gone as far as suggesting that the principle gives rise to rights held by unborn generations.³⁶ For example, in a separate opinion in Pulp Mills on the River Uruguay, Judge Cançado Trindade observed that ‘it can hardly be doubted that the acknowledgment of inter-generational equity forms part of conventional wisdom in international environmental law’, and that the principle demanded that international law be interpreted and applied with reference to the ‘long-term temporal dimension’, ‘displaying concern for seeking to secure the welfare not only of present but also of future generations’.³⁷

14.2.2 Development of the Principle in Domestic Courts in the Climate Context

14.2.2.1 Obligations Owed by States

14.2.2.1.1 Equitable Climate Mitigation Policy

The principle of intergenerational equity is frequently referred to in climate litigation. Sometimes, this is framed in terms of the ‘rights’ or ‘interests’ of future generations.³⁸ Despite some conceptual variation, the principle has shaped judicial decisions which recognise the substantive obligations of States to equitably mitigate the future effects of climate change, and to recognise environmental rights possessed by children, young people, and future generations. The Inter-American Court of Human Rights has observed that the right to a healthy environment – recognised in more than 100 national constitutions and recently by the UN Human Rights Council and the UN General Assembly³⁹ – includes an individual dimension, as well as a ‘collective dimension’ as a ‘universal value that is owed to both present and future generations’.⁴⁰ The Supreme Court of Colombia has observed in 2018 that ‘without a healthy environment, subjects of law and sentient beings will not be able to survive, much less protect those rights for our children or future generations’.⁴¹ Relatedly, at least one United States appellate judge has interpreted a ‘perpetuity principle’ as ‘structural and implicit’ in the United States Constitution, requiring a guarantee of a stable climate to ‘all future generations’.⁴² India’s National Green Tribunal has interpreted intergenerational equity consistently with sustainable development, requiring the State to ‘balance’ the objectives of environment protection and development as part of the government’s constitutional environmental duty.⁴³ Similarly, the High Court of South Africa has highlighted the link between sustainable development and the ‘principle of “intergenerational justice”’ which involves ‘a rejection of short-termism as it requires the state to consider the long-term impact of pollution on future generations’.⁴⁴

One of the first courts to recognise rights and obligations derived from intergenerational equity was the Supreme Court of the Philippines in 1993 in Minors Oposa v Factoran.⁴⁵ In that ground-breaking case, a group of children sought orders that the government cancel all existing timber licence agreements in the country and cease issuing new ones. The case was brought following decades of massive deforestation. The Court acknowledged the climate implications of the case, observing that deforestation resulted in ‘the reduction of the earth’s capacity to process carbon dioxide gases’.⁴⁶ Drawing on the obligation contained in the Philippines Constitution requiring the State to ‘protect and advance the right of the people to a balanced and healthful ecology in accord with the rhythm and harmony of nature’, the Court found in favour of the plaintiff children.⁴⁷ From this, the Court derived an obligation of ‘inter-generational responsibility’ and ‘inter-generational justice’. The Court interpreted ‘rhythm and harmony of nature’ as incorporating a duty to ensure:

[the] judicious disposition, utilization, management, renewal, and conservation of the country’s forest, mineral, land, waters, fisheries, wildlife, offshore areas and other natural resources to the end that their exploration, development and utilization be equitably accessible to present as well as future generations. Needless to say, every generation has a responsibility to the next to preserve that rhythm and harmony for the full enjoyment of a balanced and healthful ecology. Put a little differently, the minors’ assertion of their right to a sound environment constitutes, at the same time, the performance of their obligation to ensure the protection of that right for the generations to come.⁴⁸

The obligation was further developed in 2008 by the Supreme Court in Metropolitan Manila Development Authority v Concerned Residents of Manila Bay.⁴⁹ In that case the Court affirmed mandamus relief⁵⁰ requiring the appellant to repair environmental damage to Manila’s badly polluted harbour, observing that ‘[e]ven assuming the absence of a categorical legal provision specifically prodding petitioners to clean up the bay, they and the men and women representing them cannot escape their obligations to future generations of Filipinos to keep the waters of the Manila Bay clean and clear as humanly possible. Anything less would be a betrayal of the trust reposed in them.’⁵¹

In other cases, courts have drawn on intergenerational equity in fixing State obligations to take more aggressive action on climate mitigation. In 2021 in Neubauer v Germany, the Federal Constitutional Court of Germany considered a challenge to Germany’s national climate legislation.⁵² Plaintiffs – including several children – challenged the constitutionality of national legislation which set a 55 per cent reduction target in Germany’s greenhouse gas emissions by 2030, and a goal of climate neutrality by 2045.⁵³ The Act set out concrete annual targets up until 2030, but no specific post-2030 targets. Plaintiffs pointed out that the relatively modest cuts in greenhouse gas emissions prior to 2030 implied that significant cuts would be necessary in the following fifteen years to meet Germany’s 2045 net-zero goal. The plaintiffs argued that this uneven distribution violated the government’s constitutional obligation in Article 20A of the German Federal Basic Law (Grundgesetz), which provides that ‘Mindful also of its responsibility towards future generations, the state shall protect the natural foundations of life and animals by legislation and, in accordance with law and justice, by exclusive and judicial action, all within the framework of the constitutional order’.⁵⁴ The plaintiffs further argued that the deferral of drastic climate mitigation measures to the future meant that the future fundamental freedoms of future generations would be strongly curtailed, especially relative to those enjoyed by existing adult generations.

The Court accepted the latter of these arguments. It found that Article 20A set a baseline obligation on the government to mitigate climate change, and that the deferral of significant action would create ‘advance interference-like effects’ (Eingriffsähnliche Vorwirkung) which would prevent young people from enjoying their rights and freedoms in the future. Thus, ‘fundamental rights have nonetheless been violated because the emission amounts allowed by [the Act] in the current period are capable of giving rise to substantial burdens to reduce emissions in later periods … [t]he duty to afford protection against risks to life and health can also establish a duty to protect future generations’.⁵⁵ Although such generations ‘do not yet carry any fundamental rights in the present’,⁵⁶ ‘[u]nder certain conditions, the Grundgesetz imposes an obligation to safeguard fundamental freedom over time and to spread the opportunities associated with freedom proportionately across generations. As intertemporal guarantees of freedom, fundamental rights afford the complainants protection against [burdens] … being unilaterally offloaded onto the future’.⁵⁷

The decision thus pays close attention to the question of who is required to mitigate climate change. The Court found that the State had an obligation to distribute those obligations – concretised in Germany’s legislated ‘carbon budget’ – in a fair and equitable manner. This consideration of the distributional consequences of climate action is closely aligned to the principle of intergenerational equity. However, the granular level of analysis applied in Neubauer has not been employed in all climate cases concerning the interests of future generations. In other instances, courts have paid greater deference to governments’ own assessments of justice. For example, in 2015 in Foster v Washington Department of Ecology, the Supreme Court of the US State of Washington found that although the state owed public trust obligations to ‘[p]reserve, protect and enhance the air quality for future generations’, this obligation was adequately discharged simply by engaging in a rulemaking process to establish climate regulations.⁵⁸

Intergenerational equity was also discussed in the Dutch Urgenda judgments of the District Court of the Hague (2015), Court of Appeal of the Hague (2018), and the Supreme Court (2019).⁵⁹ These judgments confirmed that the risks resulting from dangerous climate change can translate into violations of the right to life (Article 2 ECHR) and the right to private and family life (Article 8 ECHR). These risks result in a duty of care by the State to do its ‘fair share’ to mitigate climate change. The court of first instance, the District Court of the Hague, ruled that this duty of care applies to both current and future generations. Furthermore, the District Court based its decision explicitly on the principle of fairness laid down in Article 3 of the UNFCCC. According to the District Court, this principle entails that a State’s climate policy ‘should not only start from what is most beneficial to the current generation at this moment, but also what this means for future generations, so that future generations are not exclusively and disproportionately burdened with the consequences of climate change’.⁶⁰ The Court of Appeal and the Supreme Court, however, did not dwell upon the question of the State’s eventual obligations towards future generations, as the risks for current generations were sufficient to establish a breach of the duty of care.⁶¹ Thus, no answer was given to the question whether rights derived from the ECHR also apply to future generations, nor was the intergenerational element of the principle of fairness further touched upon.

14.2.2.1.2 Permitting and Consent Decision-Making

Intergenerational equity has also played a role in shaping the procedural climate obligations owed by States. Specifically, courts have found intergenerational equity and the interests of future generations to be a factor that decisionmakers must take into account when setting government policy or deciding whether to permit the development of carbon-emitting projects (such as mines or power plants). For instance, in 2013, the Supreme Court of India ordered an Environmental Impact Assessment study on capping iron ore excavations in the State of Goa, taking into account the principles of intergenerational equity and sustainable development.⁶² The Supreme Court of Sri Lanka observed in 2000 that the principle ‘should be regarded as axiomatic in the decision-making process concerning the natural resources and the environment’.⁶³

Intergenerational equity is referred to in several pieces of Australian environmental and planning legislation.⁶⁴ In a series of cases, courts and tribunals in Australia have directed decisionmakers to consider the interests of future generations based on this principle. In Gloucester Resources v Minister for Planning, the New South Wales Land and Environment Court (NSWLEC) upheld the decision of the Minister of Planning to refuse permission to develop a proposed coal mine. The Court observed that ‘[t]he principle of inter-generational equity provides that the present generation should ensure that the health, diversity and productivity of the environment are maintained for future generations’.⁶⁵ In this case, ‘[t]he economic and social benefits of the Project will last only for the life of the Project (less than two decades), but the environmental, social and economic burdens of the project will continue for long after’.⁶⁶ The Court further drew on the principle of intergenerational equity in concluding that the responsible minister was required to consider the potential climate impacts of the mine before allowing the development to go ahead,⁶⁷ including indirect, downstream’ emissions – that is, emissions generated by burning the mined coal, which would subsequently be supplied to energy generators.⁶⁸

The NSWLEC in Gloucester embarked on an extensive cost–benefit analysis before arriving at the same conclusion as the responsible minister. In other cases, courts have determined that, at a minimum, decisionmakers have a procedural obligation to turn their minds to intergenerational equity. In 2006 in Gray v Minister for Planning, the NSWLEC considered a challenge to the defendant’s decision to permit the development of the Anvil Hill Coal Mine.⁶⁹ One of the issues for the Court to consider was whether the responsible minister had fulfilled his statutory duty to consider the principles of ‘ecologically sustainable development’, which included the principle of ‘inter-generational equity’.⁷⁰ The Court concluded that the principle demands that decisionmakers consider the cumulative impacts of proposed activities, rather than any single event. A cumulative approach ‘must include the effect on future generations’.⁷¹ In light of this requirement, the Court concluded that the planning process had been deficient. Specifically, the Court considered that the environmental impact assessment requirements – which set the terms of the mine’s environmental assessment – failed to take into account Scope 3 emissions resulting from the development.⁷² This omission amounted to a ‘failure of a legal requirement to take into account the principle of intergenerational equity’.⁷³ As in other cases (such as the 2019 decision of the Chilean Supreme Court in Chauhan Chauhan),⁷⁴ the Court linked the principle of intergenerational equity to the precautionary principle: both suggest a need for caution in the face of future uncertainty. Permission for the mining development was accordingly set aside. By contrast, in 2011 in Haughton v Minister for Planning and Macquarie Generation, the minister’s decision to allow the construction of a power station was upheld in part because the minister had considered the intergenerational implications of climate change, albeit at a high level of generality.⁷⁵

This jurisprudence was recently applied by the Queensland Land Court in the 2022 case of Waratah Coal v Youth Verdict.⁷⁶ In that case, the Court recommended against approvals for the development of a new coal mine in an ecologically sensitive area. The Court observed that:

The intergenerational aspect of climate change risks makes the rights of children paramount. The year 2100 is the reference point for the Paris Agreement long-term temperature goal. My generation of decision makers will be long gone, but a child born this year will be 78 in 2100. The principle of intergenerational equity places responsibility with today’s decision makers to make wise choices for future generations. The children of today and of the future will bear both the more extreme effects of climate change and the burden of adaptation and mitigation in the second half of this century. Their best interests are not served by actions that narrow the options for achieving the Paris Agreement temperature goal. This weighs the balance against approving the applications.⁷⁷

In another recent Australian case, Sharma v Minister for the Environment in 2021, a group of children challenged the minister’s decision to approve the expansion of a coal mine. Rather than alleging a failure to fulfil a statutory duty, the plaintiffs argued that the minister owed them a tortious common law duty of care. The plaintiffs were successful in the first instance. The Federal Court Judge concluded that it was ‘reasonably foreseeable’ that the extension of the mine would lead to greater harms faced by the children in the future and that the responsible minister had ‘substantial control’ over such harm.⁷⁸ The decision, however, was overturned on appeal.⁷⁹ The most important basis for the minister’s appeal was the reasoning of the federal court that formulating climate policy is a task not of judges but of democratically chosen parliaments together with the government. This issue will be discussed further in Section 14.3 below.

14.2.2.1.3 Non-Discrimination

The third context in which intergenerational equity has shaped the obligations owed by States is in equality and non-discrimination challenges brought by children and young people against governments. In this context, child and young person plaintiffs have pointed to the current and future harms that climate change will impose on their generation. Scientific research confirming the presence of such harms and their significance has played an important role in the evolving jurisprudence.⁸⁰ Such harms are significant – as the first instance court in Sharma observed in factual findings that were upheld on appeal, present children are at a heightened risk of many climate harms (such as heat waves and mental health harms), while in the future, they are more likely to experience greater health, quality of life, and financial harms.⁸¹ The extent of this risk and danger depends partly on the effectivity of the measures taken to counter climate change and to protect children from its consequences.

Despite these uneven impacts, some courts have refused to consider equality challenges brought by children and young people. These claims are particularly prolific in North America. In ENJEU v Procurer General du Canada, the Quebec Superior Court declined to certify an equality rights claim brought on behalf of Quebecers under the age of 35, finding the identification of such a group to be ‘arbitrary’.⁸² In Aji P, the Court of Appeals of Washington State determined that children were not a ‘suspect class’ that attracted equal protection rights under the United States Constitution.⁸³ This finding was based on three reasons drawn from United States equal protection jurisprudence: childhood is not an immutable characteristic; the alleged harms were not imminent; and ‘the aggregate acts of the State do not show any discrimination or discriminatory intent’.⁸⁴ The equal protection claim was accordingly rejected.

Other courts, however, have been more open to such challenges. In the 2020 Mathur v Ontario case, the Supreme Court of Ontario allowed an equality claim against the provincial government to proceed to a full merits hearing. Plaintiffs alleged that the replacement of previous climate mitigation targets with less ambitious ones constitutes age discrimination prohibited by section 15 of the Canadian Charter of Rights and Freedoms. The Court decided that the section 15 claim ‘self-evidently’ met the threshold test of having a ‘reasonable prospect of success’, given that ‘most, if not all of [the plaintiffs] will be proportionately [sic] affected by the impacts of climate change and will suffer the most of all generations; but more importantly, these impacts will exacerbate their pre-existing vulnerability and disability’.⁸⁵ Despite this initial success, however, the claim was unsuccessful at the merits stage.⁸⁶ While the Court accepted that ‘climate change has disproportionate impacts on young people and indigenous peoples’,⁸⁷ it nonetheless found that the government did not have a positive obligation to bridge ‘a gap between group and non-group members’.⁸⁸ The Court further found that the differentiated impact was not between people of different ages, but rather, ‘a temporal distinction’, and therefore not a ground protected or recognised by Canadian human rights law.⁸⁹

Recently, the UN Human Rights Committee addressed a claim brought by a number of indigenous Torres Strait islanders alleging that Australia’s failure to take effective climate mitigation and adaptation measures violated their rights under the International Covenant on Civil and Political Rights (ICCPR). In this case, known as Daniel Billy v Australia,⁹⁰ the question at hand was not discrimination against future generations in general but the specific consequences of climate policy for the indigenous groups of which the claimants were members. Substantially, the complaint involved alleged violations of the right to life and the right to privacy, family, and home life, as well as minority rights, rather than age discrimination. Nevertheless, the Committee’s jurisprudence may have important implications for age discrimination claims. The ground-breaking views of the Committee confirmed the violation of Articles 17 and 27 of the ICCPR, concerning the right to private and family life and the right of minority groups to enjoy their own culture. The Committee considered the right to culture through an intergenerational lens: it recognised that the ‘the State party’s failure to adopt timely adequate adaptation measures to protect the authors’ collective ability to maintain their traditional way of life, to transmit to their children and future generations their culture and traditions and use of land and sea resources discloses a violation of the State party’s positive obligation to protect the authors’ right to enjoy their minority culture’.⁹¹ This ruling illustrates how intergenerational equity can be effectively integrated into human rights law, thus ensuring that the rights of both present and future generations are protected through the adoption of effective climate policies.

14.2.2.1.4 Courtroom Procedure

In addition to the obligations outlined earlier, intergenerational equity plays a role in considerations of courtroom procedure and access to justice. Many judges have considered that procedural innovations are necessary in order to allow claims of intergenerational equity to be presented in court. In particular, judges have been required to consider who, if anyone, may be permitted to represent the interests of future generations; and in particular, whether children may do so. As many judges have noted, these interests are unrepresented in the political process – neither children nor future generations can vote.⁹² The Supreme Court of Pakistan observed in 2021 that intergenerational justice requires that ‘the Court should be mindful that its decisions also adjudicate upon the rights of the future generations of this country’, a ‘silent majority’ which ‘is rendered powerless and needs a voice’.⁹³ And the High Court of South Africa has found that the right to a healthy environment as protected under section 24 of the Constitution of South Africa ‘may be invoked purely for the benefit of future generations’ even if violations of the right of present generations cannot be demonstrated.⁹⁴

These considerations are central to decisions concerning standing and the certification of class actions. In Minors Oposa, the Court recognised the standing not only of the child plaintiffs to be represented in Court by their litigation guardians but for the children to ‘sue on behalf of the succeeding generations … based on the concept of intergenerational responsibility’.⁹⁵ The Court later observed that the children had standing not just as parties in themselves but also to ‘represent their generation as well as generations yet unborn’.⁹⁶ The Court formally certified the children as representatives of a class action, finding that ‘since the parties are so numerous, it becomes impracticable if not totally impossible, to bring all of them before the court. We likewise declare that the plaintiffs therein are numerous and representative enough to ensure the full protection of all concerned interests’.⁹⁷

The wide-reaching approach of the Oposa court has been influential in Filipino law. Since the 1993 decision, the Philippines has introduced writs of kalikasan, designed to streamline and liberalise standing requirements in environmental cases.⁹⁸ Nevertheless, the approach has encountered resistance in some quarters. Subsequent courts have been concerned that the approach presupposes that a single group of plaintiffs could speak for entire present and future generations, counterproductively resulting in the court making decisions on their behalf that actually preclude the full range of future decision-making. In Arigo v Swift, the Court observed that:

[w]hile ‘intergenerational responsibility’ is a noble principle, it should not be used to obtain judgments that would preclude future generations from making their own assessment based on their actual concerns. The present generation must restrain itself from assuming that it can speak best for those who will exist at a different time, under a different set of circumstances. In essence, the representative suit will inevitably result in preventing future generations from protecting their own rights and pursuing their own interests and decisions. It reduces the autonomy of our children and our children’s children. Even before they are born, we again restricted their ability to make their own arguments.⁹⁹

Judge Leonen suggested in his concurring opinion to Resident Marine Mammals of the Protected Seascape Tanon Strait v Reyes that standing and class action certification of groups on behalf of future generations should be restricted only to cases where:

a) … there is a clear legal basis for the representative suit; b) there are actual concerns based squarely upon an existing legal right; c) there is no possibility of any countervailing interest existing within the population represented or those that are yet to be born; and d) there is a threat of catastrophe so imminent that an immediate protective measure is necessary.¹⁰⁰

‘Better still’, the Court suggested, referring to the Minors Oposa case, ‘in light of its costs and risks, we abandon the precedent altogether’.¹⁰¹

This tension is evident elsewhere in the world. Many courts have followed the path forged by Minors Oposa in liberalising participation requirements to facilitate the presentation of arguments on behalf of future generations. In Demanda Futuras Generaciones, the Supreme Court of Colombia took a flexible approach to standing, permitting climate claims to be brought on behalf of children and future generations through the streamlined tutela procedure.¹⁰² In 2023 in the Belgian case of VZW Klimaatzaak, the Court of Appeal reviewed relevant human rights standards on the right to participate in environmental decision-making, and in particular, the Convention on Access to Information, Public Participation and Access to Justice in Environmental Matters (‘Aarhus Convention’). The Court concluded that the plaintiffs were entitled to bring claims on behalf of future generations, especially in light of the impacts that climate change has on the entire present and future population.¹⁰³

In the United States, plaintiffs face especially restrictive standing requirements. Plaintiffs must generally demonstrate the existence of a particularised injury; caused by the defendant; and redressable by the Court. Some child and youth plaintiffs have met these requirements, particularly before state (rather than federal) courts. In Funk v Wolf, the Commonwealth Court of Pennsylvania ultimately rejected a state constitutional law challenge to the state’s failure to develop a comprehensive mitigation plan, but it accepted that at least one child plaintiff had experienced harms that could be distinguished from the general population for the purposes of standing requirements.¹⁰⁴ The Court further recognised that the claim met the causation requirement for the purposes of standing, namely the requirement that there is a causal relationship between the defendant’s conduct and the injury suffered. The Court observed that ‘[t]he zone of interests protected by the [state constitution’s environmental provision] is the rights of all people in the Commonwealth, including future generations’.¹⁰⁵ The Court, however, rejected the claim on substantive grounds. Youth plaintiffs in at least two other state court claims – Held v Montana and Kanuk v Alaska – have likewise overcome standing restrictions. In Kanuk v Alaska, the Supreme Court of Alaska found that Alaskan state courts do not deny ‘injured persons standing on grounds that others are also injured … to require dismissal of … lawsuits because all possible viewpoints cannot be represented would create unacceptable barriers to the courts’.¹⁰⁶ And in Held v Montana, a trial court found that youth plaintiffs had standing because they experienced not only speculative future harms but already manifest harms of climate change, such as anxiety-related mental health harms.¹⁰⁷

Other courts have been more circumspect in relation to standing and class certification. In the Dutch Urgenda case, the Supreme Court did not touch upon the question whether interest groups can litigate on behalf of future generations. In the German Neubauer case discussed earlier, the standing of child plaintiffs was recognised, but only as existing persons – not as representatives of future generations. The Court observed that ‘[t]he complainants are not asserting the rights of unborn persons or even of entire future generations, neither of whom enjoy subjective fundamental rights. Rather, the complaints are invoking their own fundamental rights’.¹⁰⁸ In the ENJEU case also discussed earlier, the breadth of climate impacts was considered a reason to restrict the standing of plaintiffs purporting to represent all young people, and instead reserve the matter for the political branches.¹⁰⁹ In addition to these specific concerns related to young people and future generations, as discussed elsewhere in this volume, some courts have drawn on general separation of powers concerns or the political question doctrine to preclude judicial consideration of claims related to intergenerational equity. Such decisions are particularly common in North America.¹¹⁰

Finally, it should be noted that child and youth participation may extend beyond formal matters such as standing and class action certification, to issues related to the accessibility and age-appropriateness of procedures. In Sacchi for example, the CRC considered a communication brought by children from several countries who argued that inaction on climate change violated their rights under the UN Convention on the Rights of the Child. The communication was unsuccessful on the basis that the children had failed to exhaust domestic remedies, a prerequisite for the Committee to consider the complaint.¹¹¹ Nevertheless, the Committee engaged with the complainants by communicating their decision in a plain-language document, intended to be legible to the child complainants, while also adopting a closed-door hearing procedure that allowed the child petitioners to address the Committee directly. Moreover, the complainant Chiara Sacchi and other children were invited to participate in a special advisory team on climate and children’s rights. The Committee also organised an online consultation among children and youth to gain a better understanding of the ways in which children’s rights are affected by climate change and environmental degradation. These measures suggest the potential for greater innovation in facilitating the access of children and young people to judicial decision-making on climate issues.

14.2.2.1.5 Remedies

Intergenerational equity concerns may play a role in remedies awarded in climate cases. The principle suggests that remedies must be effective over a long-term horizon, rather than satisfying the short-term demands of the parties.

Tailoring judicial remedies to the needs of future generations is no easy task. Courts have referred to the need for such tailoring, but explicitly crafted remedies remain rare. In the 2018 Shrestha v Prime Minister case, the Supreme Court of Nepal found that the Nepali government owed a constitutional obligation to legislate a comprehensive climate mitigation and adaptation policy. It ordered the government to ‘make legal arrangements to ensure ecological justice and environmental justice to the future generation’, but gave little guidance as to how such an outcome could be achieved.¹¹² In VZW Klimaatzaak, the Belgian Court in the first instance explicitly declined to specify a remedy, despite finding that the government had violated plaintiffs’ rights.¹¹³ More extensive guidance was provided by the Federal Constitutional Court of Germany in Neubauer. Although it was left to the legislature to amend the challenged legislation, the Court set out principles to guide that amendment, including a requirement that annual emission amounts and reduction targets be set out in greater detail.¹¹⁴ The Dutch Urgenda judgments show a thoroughly considered level of detail with the District Court of the Hague partly basing its emission reduction order on the principle of intergenerational equity.

A more novel and comprehensive scheme was set out by the Supreme Court of Colombia in Demanda Futuras Generaciones. In that case, youth plaintiffs challenged the government’s failure to control logging in the Amazon Rainforest, in part because of logging’s effect on climate change. The Court recognised the Amazon Rainforest as a subject of rights (sujeto de derecho), effectively recognising the rainforest as a legal person. It also ordered several government agencies, together ‘with the active participation of the plaintiffs, affected communities, scientific organizations or environmental research groups, and interested populations in general’, to develop an ‘intergenerational pact for the life of the Colombian Amazon’ that includes ‘measures aimed at reducing deforestation to zero and greenhouse gas emissions’ and has ‘national, regional and local implementation strategies of a preventative, mandatory, corrective and pedagogical nature, directed toward climate change adaptation’.¹¹⁵ The Court further set out a process for judicial oversight to monitor the implementation of the remedy. It should be noted that many groups, including the plaintiffs, have complained that the remedy has not been implemented by the Colombian government.¹¹⁶ Similar remedy mechanisms are available elsewhere, such as in the Philippines, where the writ of continuing mandamus has been applied in environmental cases to ensure long-term court oversight and action plans.¹¹⁷

Another novel remedy in the environmental context was awarded in the Argentinian case of Fischer v Comune Dique Chico. The case concerned an agricultural school which challenged the government’s decision to allow inorganic fumigation and fertilisation to take place in the surrounding area. The Court found the decision to be unconstitutional and emphasised the importance of environmental education, finding that children should be taught about the importance of intergenerational equity. As part of the remedies awarded in the case, the Court ordered the judgment to be taught in nearby schools for ‘pedagogical-environmental purposes’.¹¹⁸ The Court observed that was ‘a cultural way of strengthening generational equity’, demonstrating that ‘present generations should not – we must not – adopt environmental decisions that irreversibly compromise them as future generations … [f]or this reason, the corresponding copies [of this decision] will be sent to them’.¹¹⁹

Lastly, the UN Human Rights Committee has issued extensive recommendations in the previously mentioned Billy case. The Committee determined that the State has an obligation to effectively remedy the damage suffered by the victims of the established human rights violations. This obligation entails among others an obligation to make full reparation and to provide adequate compensation for the harm suffered and to ‘engage in meaningful consultations with the authors’ communities in order to conduct needs assessments; continue its implementation of measures necessary to secure the communities’ continued safe existence on their respective islands’.¹²⁰

14.3 Emerging Best Practice

We consider ‘emerging best practices’ to be those judicial practices which best give practical effect to the principle of intergenerational equity, or which ensure adequate application of the principle in judicial decisions. The principle requires consideration of the obligations owed by the present to future generations. One overriding obligation is clear: intergenerational equity requires that States introduce policies to ensure rapid decarbonisation and climate mitigation, and to adapt to current and future effects of climate change. The absence of such policies is fundamentally inconsistent with the principle of intergenerational equity.¹²¹ When cast in terms of intergenerational distribution, the rapid emission of greenhouse gases into the atmosphere amounts to one generation imposing hardship and burdens on another. The adoption of an expressly distributional approach in Neubauer fundamentally exposed this. The intergenerational injustice of climate change is clear, whether approached expressly from the standpoint of a right to a healthy environment (as in Minors Oposa v Factoran), or through general principles and obligations (as in the dissenting opinion of Judge Staton in the 2020 case of Juliana v United States).

In addition to this high-level, overriding obligation, we set out six more specific emerging best practices: (1) consideration of the distributional impacts of climate policies; (2) requiring consideration of long-term and downstream climate effects in planning and permitting decisions; (3) recognising and admitting age discrimination cases that relate to climate change; (4) a flexible approach to the standing and class certification; (5) fostering children and young people’s participation in courtrooms; and (6) crafting judicial remedies which promote long-term and participatory implementation.

Best practice involves paying attention to the fair distribution of climate obligations. The approach taken in the Neubauer decision is a strong instantiation of intergenerational equity. The Court went beyond Germany’s high-level climate policy targets and conducted a distributional assessment of who would bear the burden of reaching them. The analysis reveals how climate policies, in addition to climate change itself, have distributional consequences. The Court drew on well-established constitutional jurisprudence in finding that the State could not unduly interfere with children’s rights and freedoms in the development of climate mitigation policies, requiring the German parliament to revisit its approach. This distributional assessment reflects best practice. Such an approach is particularly crucial in jurisdictions which recognise an explicit right to a healthy environment,¹²² but it may be applied – as in Neubauer – even in jurisdictions where no such subjective right exists. By contrast, we consider that it is insufficient for courts to simply note that a government has, or is considering, a climate mitigation policy, even where such a policy may be ambitious in absolute terms (such as a long-term net-zero target).¹²³ Such an approach fails to apply considerations of fairness and justice as demanded by the principle of intergenerational equity.

Secondly, emerging best practice involves the application of intergenerational equity considerations in permitting and planning decisions. Depending on the overall decision-making framework and the task of the reviewing court, such applications may be either substantive or procedural. At a minimum, decisionmakers should be expected to turn their minds to the long-term impact of greenhouse gas emitting projects (such as mines, power plants, and airports) and the renewal of infrastructure necessary for climate adaptation. This includes downstream consequences, such as the Scope 3 emissions considered in Gray v Minister for Planning. More ambitiously, judges could consider whether to recognise supra-statutory obligations owed by decisionmakers to young people, as the trial court did in Sharma. Where a court is entrusted with reviewing the merits of planning decisions, judges themselves should inquire into downstream climate consequences. The Gloucester Resources and Waratah Coal cases discussed earlier demonstrate how judges can apply the principle of intergenerational equity when engaging in cost–benefit analysis or merits review of permitting decisions.

Thirdly, emerging best practice reinforces the relevance of anti-discrimination and equal protection law. As numerous scientific and judicial bodies have recognised, children and young people face existing and future vulnerabilities as a result of climate change policies.¹²⁴ These consequences are entirely the fault of prior generations but will be borne by subsequent ones. This should be recognised as a form of substantive age discrimination, regardless of intent.¹²⁵ Alternatively, some have suggested a new ground of discrimination of ‘birth cohort’ discrimination – that is, differentiated impact that will arise in the future as a result of the timespan in which a cohort of people have been born.¹²⁶ The preliminary decision of the Supreme Court of Ontario in the Mathur decision is an example of emerging best practice and demonstrates the importance of recognising the differentiated impact of climate change. The subsequent decision on the merits, which rejected the existence of a positive obligation on governments to remediate age-based differentiated impact, should not be considered emerging best practice. By contrast, the Billy decision of the UN Human Rights Committee shows how protection of the rights of those who suffer the most from the consequences of climate change can be ensured while keeping in mind the intergenerational dimension of the right to culture.

Fourthly – and relatedly – emerging best practice demonstrates a flexible approach to standing and class certification. Courts should consider the fact that children and young people are generally excluded from the political process, most obviously by being unable to vote. Courts may thus offer one of the few options for children and young people to participate in climate decision-making. This judicial role was forcefully articulated in Minors Oposa v Factoran. Courts should be careful not to erect too many barriers to children’s access to the courtroom. This does not necessarily imply that judges should exceed the bounds of their proper constitutional role. As Filipino courts have suggested in cases since the Minors Oposa decision (such as Arigo v Swift and the Marine Mammals case), it will often be appropriate for judges to inquire whether child plaintiffs in the particular case are appropriately representative of a broader class of children, or of future generations more generally. But where interests are broad and collective – such as where courts are called upon to review the validity of continuing national climate policies – child plaintiffs may play an important role in articulating the long-term interests at stake. Furthermore, as the trial court recognised in Held v Montana, harm to children is not merely speculative: it is already manifest, thus meeting the requirement for many injury-based standing tests in national law. The scale of the climate crisis should not be used as a reason to preclude such standing, as occurred in the Juliana decision. Judges can play a role in climate governance through more modest declaratory remedies concerning the validity of particular laws and policies, as recognised in the preliminary decision in Held v Montana.

Fifthly, once admitted into the courtroom, judges could consider how to facilitate children and young people’s ability to participate in judicial decision-making. Rights of participation and access to justice are broadly recognised in IEL and international human rights law and could be better reflected in domestic courtroom processes.¹²⁷ The CRC’s decision in Sacchi v Argentina suggests some basic possibilities, such as the use of closed-door hearings or presentation of evidence, and plain-language communication of decisions. Such procedures will not be appropriate in all cases – indeed, open justice considerations may preclude the possibility of closed-door hearings. Where local rules of procedure permit, judges could consider other mechanisms through which to foster youth participation. This issue was canvassed in the CRC’s General Comment No 26 on children’s rights and the environment with a special focus on climate change, which in turn clarified the relevance of the UN Convention on the Rights of the Child to climate litigation.¹²⁸

Finally, emerging best practice suggests the importance of remedies that will promote the long-term interests of children and young people. This is a challenging task for any court. Even carefully structured remedies mandating judicial oversight, such as those crafted in Demanda Futuras Generaciones, may fail in implementation. But where such remedies are available – as in the Philippines, which permits the use of continuing mandamus remedies in environmental matters – they may offer opportunities for children to play a role in future decision-making and governance. More novel approaches, such as the pedagogical orders made by the Argentinian court in Fischer, may also foster children’s participation in environmental and climate governance. Recognising the Rights of Nature, as occurred in Demanda Futuras Generaciones, may also facilitate children’s participation where they are accompanied by participatory governance structures to make decisions on Nature’s behalf. Even where such remedies are not available and implementation will necessarily be left to the political branches, clearly specifying the requirements of intergenerational justice in judicial orders can help to integrate intergenerational equity in subsequent legislative and policy decisions. Moreover, the recommendations in the UN Human Rights Committee’s Billy case suggest that reparations can be used in order to remedy climate damage that has already occurred and reverse, as far as possible, its consequences. Together with measures to mitigate future damage, this remedy could play an important role in ensuring intergenerational equity before the courts.

14.4 Replicability of Best Practices

Intergenerational equity is an increasingly recognised principle of IEL. As such, all States have an obligation to integrate it into their domestic frameworks. The precise form of such integration, however, will inevitably vary between jurisdictions. Where a right to a healthy environment is recognised, such a right should be interpreted as incorporating the principle of intergenerational equity into domestic law. This has been recognised by the Supreme Court of the Philippines in Minors Oposa,¹²⁹ the Inter-American Court of Human Rights,¹³⁰ and the Mexican District Court in Greenpeace Mexico.¹³¹ In other instances, such as Australia, intergenerational equity will be referenced in domestic legislation. Even where it is not explicitly referenced in domestic law, it may operate as an interpretive principle or relevant consideration.

Furthermore, the form and extent of implementation will be dictated by doctrine and rules of procedure. In some jurisdictions, judges and rule makers have already integrated principles of intergenerational equity in relaxed standing requirements (as in Minors Oposa and subsequent development of the writ of kalikasan in the Philippines) or allowing environmental matters to be brought under more streamlined judicial procedures (as reflected in the Supreme Court of Colombia permitting the Demanda Futuras Generaciones case to be brought as a tutela action). In systems with relatively strict or inflexible procedural requirements, the principle of intergenerational equity may not permit judicial innovation on issues such as standing, remedies, and certification of class actions.

Nevertheless, judges will often be able to develop the law to better reflect the evolving obligations of States to incorporate intergenerational equity into domestic decision-making. We consider that all of the best practices identified in this chapter are in some way applicable to the legal systems of most States. Whatever the form in which intergenerational equity is applied, its function should permeate all aspects of judging in the context of climate change.

14.5 Conclusion

In this chapter we have canvassed judicial practice from a wide range of jurisdictions. We have underscored the importance of intergenerational equity as a principle of international and domestic law, emphasising that it demands ambitious action on climate change. The principle introduces a distributional framework that judges can apply when considering claims, especially those made by children, young people, and representatives of future generations. Emerging best practice recognises that the principle entails a set of obligations that States owe to children and young people, including fairness in overall climate policy, consideration of future interests in decision-making, and recognition of the generationally differentiated impacts of climate change. Furthermore, such practice often involves flexibility and innovation in judicial procedure and remedies. Intergenerational equity is a cross-cutting legal principle which is likely to play a growing role as youth-led climate litigation continues to proliferate across the world. By applying this principle in their decisions, judges can ensure that future generations are not left to bear the burden of the current generation’s failure to take appropriate action on climate change.