Climate engineering is the ‘deliberate large-scale manipulation of the planetary environment to counteract anthropogenic climate change’.Footnote ¹ Climate engineering technologies can be divided into two broad categories: carbon dioxide removal (CDR), and solar radiation management (SRM). CDR aims to remove heat-trapping carbon dioxide (CO₂) directly from the atmosphere and store it in terrestrial or oceanic sinks. SRM aims to reflect a portion of sunlight away from the Earth to cool global temperatures. In its October 2018 special report on limiting global warming to 1.5°C above pre-industrial levels, the Intergovernmental Panel on Climate Change (IPCC) indicated that CDR will have an important role to play in limiting the risk and severity of climate change impacts.Footnote ² According to the IPCC, ‘[a]ll pathways that limit global warming to 1.5°C with limited or no overshoot project the use of [CDR] on the order of 100–1000 GtCO₂ [gigatonnes CO₂] over the 21^st century’.Footnote ³ The IPCC did not include SRM in its modelling pathways,Footnote ⁴ but proponents suggest that SRM may also have an important role to play in preventing global mean temperatures from overshooting the Paris Agreement targets, which aim to keep global average temperature increases well below 2°C.Footnote ⁵ Climate engineering is therefore emerging as an increasingly important tool for responding to climate change.

Climate engineering, however, presents significant governance challenges. CDR and SRM technologies may have negative environmental impacts and some proposals, such as stratospheric aerosol injection, pose risks of transboundary harm.Footnote ⁶ Many technologies are yet to be tested beyond computer modelling and/or laboratory settings, and scientists are therefore uncertain as to their efficacy, feasibility, and side effects.Footnote ⁷ Some sceptics of climate engineering also fear that the research and development of climate engineering technologies might detract from conventional mitigation efforts.Footnote ⁸ Climate engineering technologies additionally raise questions about procedural and distributive justice.Footnote ⁹ For example, who should determine if and when climate engineering technologies are to be used?Footnote ¹⁰ To what extent should the general public be consulted regarding climate engineering activities?Footnote ¹¹ Climate engineering technologies may have disproportionate impacts on different regions, which raises questions as to whether state and/or non-state actors can be compensated for any losses suffered.Footnote ¹² These issues require the development of robust governance mechanisms. It is therefore important to understand how domestic and international law might contribute to climate engineering governance.

Climate Engineering and the Law is a timely contribution to scholarship on this issue. The book is a collection of chapters by established researchers in the field of climate engineering governance, edited by legal scholars Michael B. Gerrard and Tracy Hester. The overall purpose of the book is to examine the extent to which existing international and United States (US) domestic laws meet the governance challenges posed by climate engineering technologies. The book also aims to promote further consideration of the role that international and domestic law should play in the future development and deployment of these technologies.

Gerrard begins in Chapter 1 by explaining what climate engineering is and how CDR and SRM might contribute to climate change policy alongside conventional mitigation and adaptation strategies. Gerrard also introduces each chapter and gives an overview of the governance challenges and legal frameworks analyzed therein. In Chapter 2, Eli Kintisch examines prominent CDR and SRM technologies, including stratospheric aerosol injection,Footnote ¹³ bioenergy with carbon capture and storage (BECCS),Footnote ¹⁴ and ocean fertilization.Footnote ¹⁵ Kintisch explains the scientific principles that underpin each technology, describes the current stage of development (i.e., whether research has progressed to field testing), and highlights potential challenges for research and/or deployment. Such challenges include negative environmental impacts, limitations for large-scale deployment,Footnote ¹⁶ and commercial interest in the development of some technologies.Footnote ¹⁷ These explanations are concise, and readers wishing for more detailed evaluations may want to consult additional sources.Footnote ¹⁸ Kintisch nevertheless provides readers with the necessary technical background that underpins the following chapters.

In Chapter 3, Jesse Reynolds examines how rules of international law might apply to climate engineering technologies. At almost 150 pages, this chapter is extremely comprehensive. Reynolds provides a detailed analysis of pertinent international agreements, including the Paris Agreement,Footnote ¹⁹ the United Nations Convention on the Law of the Sea (UNCLOS),Footnote ²⁰ and the ocean dumping regime,Footnote ²¹ as well as rules of customary international law. Reynolds also considers international agreements often overlooked in geoengineering governance literature, such as the 1998 UNECE Convention on Access to Information, Public Participation in Decision-Making and Access to Justice in Environmental Matters (Aarhus Convention),Footnote ²² the Antarctic treaty system,Footnote ²³ and principles of international environmental law, including the principles of common but differentiated responsibilities (CBDR) and intergenerational equity. In doing so, Reynolds emphasizes the challenges that climate engineering technologies pose for international law and the need for legal scholars with different expertise to engage with this topic.

The book then moves from the international sphere into the domestic. In Chapter 4, Albert Lin considers relevant state and federal law in the US. In Chapter 5, Hester examines the issue of liability and compensation for harm from climate engineering activities and considers potential liability mechanisms under international and US law. Domestic law is likely to play an important role governing geoengineering research in the near term, especially as laboratory research and computer modelling lead into small-scale outdoor experiments. As this book points out, some CDR technologies are unlikely to have significant transboundary impacts and may therefore require governance only at the domestic level. However, to date, there has been limited legal scholarship on the capacity of domestic law to govern climate engineering.Footnote ²⁴ These chapters therefore make an important contribution to the literature by considering the extent to which US domestic law – including environmental protection legislation, weather modification laws, and tort law – may govern climate engineering technologies. The chapters suggest that existing domestic law may provide a rudimentary governance framework for some climate engineering technologies in the US, but these laws were not developed with climate engineering in mind. More targeted rules will therefore need to be developed to comprehensively govern climate engineering technologies in the US.

In Chapter 6, Michael Burger and Justin Gundlach focus on the governance of climate engineering research (as opposed to full-scale deployment). They argue that effective governance is necessary for research to progress. As part of this chapter, Burger and Gundlach examine the Asilomar and Oxford principles, which are voluntary codes of conduct developed by scientists and social scientists to govern climate engineering research.Footnote ²⁵ These principles call for research to be conducted responsibly and transparently, with independent assessment and public engagement. Burger and Gundlach consider how these general principles might be implemented in climate engineering research projects – for instance, in how research funding is allocated, and the extent to which the public is informed and consulted regarding a climate engineering project. Gerrard and Hester conclude the book in Chapter 7 by recommending the further development of international and US domestic law to better meet the governance challenges posed by climate engineering. For climate engineering activities likely to have transboundary effects, this chapter recommends developing a new international agreement under the auspices of the United Nations Framework Convention on Climate Change (UNFCCC).Footnote ²⁶ It also identifies governance elements that will need to be addressed by such an agreement, such as processes and principles to authorize climate engineering activities, procedures for public deliberation, and liability and compensation mechanisms.

Climate Engineering and the Law is a useful source of information about this evolving area of climate change policy and governance. The editors and contributors have expertly pitched the book to an interdisciplinary audience. It provides clear, non-technical explanations of climate engineering proposals based on the latest scientific research. The book therefore offers international and environmental law scholars an up-to-date introduction to key CDR and SRM proposals and the governance challenges they pose. The analysis of international and US domestic law is extensive and raises broader questions about the capacity of these legal systems to govern emerging technologies. However, this analysis is not targeted exclusively at a legal audience. The authors have made a conscious effort to explain fundamental legal terms and concepts. For example, Chapter 3 provides concise explanations of the principle of state sovereignty and the formation of customary international law. The legal analysis in this book is therefore accessible to readers from other disciplines.

Unfortunately, the book does not analyze domestic legal systems outside the US. While the consideration of US tort law in Chapter 5 will be of interest to legal scholars from common law jurisdictions, the analysis of domestic law may otherwise be of limited use to legal scholars and climate engineering researchers outside the US. By focusing only on US domestic law, the editors have also missed an opportunity to develop a comparative analysis of climate engineering governance under different domestic legal systems.

These concerns aside, Climate Engineering and the Law skilfully demonstrates that existing international and domestic law will play an important role in the governance of climate engineering technologies, but more targeted rules are needed to fill gaps in existing frameworks. Given the assumptions about the future availability and use of climate engineering technologies in modelling scenarios, it is essential that climate change lawyers are well-informed about these proposals and are prepared to contribute to the development of international and domestic governance. Climate Engineering and the Law is therefore an essential read for climate change lawyers. Climate engineering is the next big challenge for climate change law and policy. We hope that this book will inspire a new wave of critical legal scholarship on this issue, especially on the capacity of other domestic legal systems to govern climate engineering technologies.