The use of technological and chemical means aiming to achieve favorable weather conditions or reduce the risk of weather extremes is known as Weather Modification (WM). The United States of America, the People’s Republic of China, Thailand, the United Arab Emirates, and Europe have employed WM in an effort to prevent hurricanes and storms, control precipitations, mitigate deforestation and drought, and enhance agriculture. Recently, the use of WM has been expanded toward decreasing air pollution and creating favorable weather conditions for major political and athletic events. The increasing significance and use of WM call for consideration upon its positive and negative effects on human health, close collaboration among health experts and WM decision makers, and relevant public health emergency contingency planning.

Most domestic environmental laws control the act of emitting pollutants into the environment. As a result, they do not apply squarely to negative emissions technologies (NETs) that remove ambient contaminants and do not emit pollutants themselves. As a result, current US environmental laws cannot readily govern a NET unless it has features that would typically allow regulation of a clean-up, such as ownership of the polluted resources, being at fault for polluting them or instituting projects to restore them. We should reinterpret such laws to focus on actual disruption or harm to the environment instead of using emission of pollutants as a proxy for ecological damage.

In the rapidly expanding literature on the ethics of climate engineering, a lot has been made of the fact that stratospheric aerosol injection would for the first time create a world whose climate had been intentionally shaped by deliberate human decisions. Intention has always mattered in ethics. Due to the importance of intention in assigning culpability for harms, one might expect that the moral responsibility for any harms created during an attempt to reconstruct the global climate using stratospheric aerosols would be considerable. This article investigates such an expectation by making a comparison between the culpability for any unintended harms resulting from stratospheric aerosol injection and culpability for the unintended harms already taking place due to carbon emissions. To make this comparison, both types of unintended harms are viewed through the lens of the doctrine of double effect. The conclusion reached goes against what many might expect. The article closes by suggesting that a good way to read this surprising conclusion is that it points toward the continuing moral importance of prioritizing emission reductions.

Christopher J. Preston's use of the doctrine of double effect to claim that hypothetical climate engineers might very well be less culpable for climate harms than those who continue to emit greenhouse gases is unpersuasive. His argument rests shakily on the ability to determine and quantify climate harms and to distinguish forensically between their causes. He is also largely silent about the distributional effects of these harms and their ethical and political ramifications.

In his article “Carbon Emissions, Stratospheric Aerosol Injection, and Unintended Harms,” Christopher J. Preston compares the culpability of carbon emitters versus that of geoengineers deploying stratospheric aerosol injection (SAI). This comparison relies on a parallel between carbon emitters and SAI deployers that requires both to be agents. However, both are not. While the harms of geoengineering will be caused by culpable agents acting intentionally, the harms connected to climate change emerge out of the uncoordinated actions of billions of people. Taken as a large group, carbon emitters cause harm but do not constitute an agent. Taken individually, carbon emitters are agents but do not cause the harms of climate change. As a result, the parallel collapses, and Preston's “surprising” conclusion is one that he is not entitled to reach.

In order to advance a neatly deductive argument, Christopher J. Preston must make a number of assumptions and framing decisions that exclude important practical points from the scope of his analysis. We do not criticize him for doing so, as these simplifications allow him to advance a concise argument about an ethically complex subject. However, as scholars of politics and law, we are interested in what this ethical argument means—and does not mean—for the messy politics of climate engineering. Accordingly, in our response we unpack the political implications of some of Preston's assumptions and framing decisions in an effort to add a layer of practical richness to the abstraction of Preston's analysis.

The prospect of climate engineering (CE) – also known as geoengineering, referring to modification of the global environment to partly offset climate change and impacts from elevated atmospheric greenhouse gases – poses major, disruptive challenges to international policy and governance. If full global cooperation to manage climate change is not initially achievable, adding CE to the agenda has major effects on the challenges and risks associated with alternative configurations of participation – for example, variants of partial cooperation, unilateral action, and exclusion. Although the risks of unilateral CE by small states or non-state actors have been over-stated, some powerful states may be able to pursue CE unilaterally, risking international destabilization and conflict. These risks are not limited to future CE deployment, but may also be triggered by unilateral research and development (R&D), secrecy about intentions and capabilities, or assertion of legal rights of unilateral action. They may be reduced by early cooperative steps, such as international collaboration in R&D and open sharing of information. CE presents novel opportunities for explicit bargaining linkages within a complete climate response. Four CE-mitigation linkage scenarios suggest how CE may enhance mitigation incentives, and not weaken them as commonly assumed. Such synergy appears to be challenging if CE is treated only as a contingent response to a future climate crisis, but may be more achievable if CE is used earlier and at lower intensity, either to reduce peak near-term climate disruption in parallel with a programme of deep emission cuts or to target regional climate processes linked to acute global risks.