Solar geoengineering (also known as solar radiation management) is, by Jesse Reynolds’ reckoning, an objectionable proposition that nevertheless demands attention. In The Governance of Solar Geoengineering, Reynolds offers a sweeping review of existing scholarship, policy proposals, and real-world efforts to steer a nascent and contentious set of climate change response options. The book then goes further to propose a set of steps that might be taken to fill governance gaps and to guide development of solar geoengineering from research through large-scale deployment.

Reynolds begins by summarizing the existing state of the computer modeling, physical science, and engineering research on solar geoengineering. The basic idea behind solar geoengineering is that boosting the reflection of incoming shortwave solar radiation back into space can cool the planet. The book traces early thinking along these lines back to the mid-1960s. From that time forward a number of different ideas to reflect sunlight have been mooted, from increasing the reflectivity of ground-level terrestrial or oceanic features (think lots of white roofs or reflective films spread on bodies of water), to the artificial brightening of marine clouds, to the introduction of sulfate particles into the upper atmosphere (this last option is usually called stratospheric aerosol injection). The latter two ideas in particular show promise, based on natural analogues and computer modeling, as ways to reduce certain of the impacts associated with climate change. At the same time solar geoengineering options pose an array of physical and social risks, such that, in Reynolds’ measured words, “governance would be beneficial” (p. 31).

The middle section of the book unpacks and offers commentary on the scholarship and practical moves that have been made on solar geoengineering governance. It first looks at the problem structure of solar geoengineering from the vantage of international relations theory and practice. Stratospheric aerosol injection in particular could conceivably be undertaken by a single state or even a wealthy individual. This raises a set of questions about coordinating action, the control of potential rogue actors, and optimization of an activity that at scale would have the character of a global public good. Reynolds usefully engages with these questions and others, summarizing existing scholarship in an accessible fashion.

The book then considers the governance of solar geoengineering from the perspective of international law. Though solar geoengineering proposals are nascent at best, with research work currently confined almost exclusively to computer modelling, there has been a great deal written about how international law might come to bear on solar geoengineering options. Parties to the Convention on Biological Diversity have made decisions and and an amendment has been proposed to the London Protocol to the London Dumping Convention related to geoengineering. Reynolds works in a systematic fashion through general relevant principles and norms of international law, regimes and organizations having to with the climate and atmosphere, human rights regimes and principles, and a selection of multilateral agreements pertaining to other domains, to show how the existing system of international law might affect the development and particularly the use of solar geoengineering approaches. The punchline is that there is already an architecture in place that could manage solar geoengineering. That said, some notable gaps in the ability of international law to handle, for instance, the specific expressions of liability and compensation for harm that solar geoengineering entails suggest the need for additional governance steps. Chapters on existing US domestic law and its bearing on and the roles of nonstate actors in governance round out the book’s middle section.

The chapters that are organized expressly to look at existing scholarship and activity on domestic and international governance are bracketed by chapters that are a little harder to characterize. Chapter 3 stands apart as a meditation on what has been called the moral hazard challenge, renamed by Reynolds the “emissions abatement displacement concern” (p. 32). The concern is that contemplation or development of solar geoengineering responses might negate or distract from efforts to rein in greenhouse gas emissions. This possibility is often raised by those skeptical of or hostile to solar geoengineering research efforts. Reynolds, by contrast, thinks the emissions abatement displacement concern is basically bunk. He argues, via thought experiments and comparison with early days of the climate adaptation conversation, that the concern is not really grounded in how people are truly likely to respond to solar geoengineering but rather in “issues of political coalitions and wider worldviews” (p. 53).

The unpacking of the moral hazard claim hints at a broader aim of Reynolds’ book—a defense of and call for a particular kind of examination of solar geoengineering. Full articulation of this broader aim, however, is reserved for the book’s short conclusion, where he says that the main problem with solar geoengineering is that its “discourse is unduly driven by intuition, ideology, and pre-existing conclusions instead of empiricism and rationality” (p. 222). Reynolds points out a number of times that current modeling research suggests that certain kinds of deployment of solar geoengineering options could reduce climate risk for just about everyone. Rather than come out directly, though, and argue for solar geoengineering research or a clear role for solar geoengineering as a climate change response option, the book strives for almost its entire length for scholarly disengagement. The result is a burying of some of the most important of the book’s contributions. The final substantive chapter and conclusion, where Reynolds paints his own picture of solar geoengineering governance and rails against too-easy dismissal of a role for solar geoengineering technologies, finally reveal where the book has been headed all along. The book would have been all the stronger had it opened with the kinds of provocations with which it closes. Even those who most strongly disagree with Reynolds’ ultimate positions will be forced to think by his careful argumentation.