Notes from a recent workshop on mitigating the effects of climate change through the global geoengineering strategy of solar radiation modification.
Cutting global greenhouse gas emissions enough to deliver on the temperature goals of the Paris Agreement is an increasingly daunting prospect. With climate change impacts occurring around the world, policymakers, stakeholders, and the public are exploring ways to reduce the human suffering of a warming planet. Solar radiation modification (SRM), also known as solar geoengineering, has received growing attention as a potential additional approach to mitigate the risks of a changing climate.
On September 19–20, 2024, Resources for the Future and the Harvard Solar Geoengineering Research Program at the Salata Institute for Climate and Sustainability organized the third annual conference on SRM and the social sciences. Taking part in the conversation were 47 participants in person, with several dozen more joining online. Presenters and moderators came from 12 countries, with strong Global South representation. Here, we summarize some of the major themes that arose. Interested readers can check out the full suite of videos and presentations on the webpage of the event.
This year’s workshop focused on gaining a better understanding of cooperative and noncooperative approaches to the governance and deployment of SRM. Cooperative approaches, with a globally agreed-upon strategy, appear relatively more attractive but raise the question of how such an agreement would arise and under what conditions. Noncooperative approaches, such as unilateral deployment by a single country or small group of countries, raise questions about national capacities and the potential strategic responses of other nations.
The technical and scientific dimensions of SRM have important implications that can inform social-science analyses of its governance and use, both cooperatively and noncooperatively. For example, SRM typically is viewed as a relatively quick way to respond to climate change. But data may be necessary from a decade or more of SRM deployment before a scientific assessment could identify and distinguish the cooling effect of a global SRM intervention against the backdrop of climate change and natural climatic variability. Such a lengthy time between action and evidence of impact raises questions about the ability of politicians, who typically want a quick demonstration of success, to stick with the intervention.
Assuming policymakers do stick with an initial intervention, the deployment ultimately would need to continue for decades to avoid serious risks. An oft-envisioned scenario is a long-duration SRM intervention, coupled first with eliminating net emissions of greenhouse gases from anthropogenic activities, and then shifting to a strategy of achieving negative emissions which would reduce atmospheric concentrations of greenhouse gases. The SRM intervention would be scaled back in tandem with efforts to mitigate the underlying drivers of climate change, avoiding the worst warming that would result from peak concentrations of greenhouse gases. If an intensive intervention halted unexpectedly for an extended period, however, the Earth would rapidly heat back up to a level that matches the background level of greenhouse gas concentrations, creating a “termination shock” that has adverse consequences.
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Stratospheric aerosol injection (SAI) is the technology that’s most often discussed in the context of SRM, but the use cases depend on who could eventually deploy it. In particular, the engineering, logistical, and technical characteristics of SAI likely limit the number of actors or countries that could deploy this technology or even undertake relevant research. As the capacities for SAI overlap with the capacities common to countries which are powerful in terms of their military and industry, interactions with the geopolitics of the day seem a given under most scenarios.
“Capacity to deploy” is not binary, either: Some parties may develop capacities that are limited to certain types of intervention, or to certain regions. Because long lead times are involved with related technologies (e.g., specialized high-altitude aircraft) and supply chains, capacities among rival countries may change over time.
A well-designed SAI intervention would be expected to bring global benefits on average, but uneven effects would be likely, and a poorly designed intervention could be bad. For example, an actor that’s motivated to use SRM to counter the melting of Arctic sea ice also would need to commit to an Antarctic program to avoid negative global climate perturbations. Even a well-designed and globally balanced SAI intervention, while bringing benefits in the form of slowed or stabilized temperature, could result in some regions around the world experiencing changed precipitation patterns that are worse than under future climate change.
While the governance of SRM appears challenging, some useful analogues exist and could inspire further social science research. The construction of hydropower dams often is a unilateral (and not necessarily well-coordinated) policy choice with significant trans-boundary impacts on water supply and biodiversity. If SRM is seen as a potential “great power” capability, international agreements such as the Partial Test Ban Treaty could be seen as a useful analogue. Neither is the composition of the atmosphere unchartered territory for international diplomacy: in addition to the United Nations Framework Convention on Climate Change, we have the Montreal Protocol on ozone-depleting substances and the treaty on preventing hostile environmental modification that’s commonly known as ENMOD.
Despite a focus on global interventions, the governance of SRM—and future research—should reflect that not all forms of SRM need to be global in scale or several decades in duration. In fact, a greater exploration of smaller types of intervention, which may be linked to mitigating particularly harmful local climate impacts, might benefit the SRM debate as a whole. Work already is underway that explores the preservation of the Great Barrier Reef through the geoengineering technique of marine cloud brightening. Other use cases might address regional, episodic weather events—droughts, heat waves, cyclones, and the like. Indeed, the strongest demand for SRM could occur in these sub-global, but still trans-boundary, cases. These examples also imply that SRM should not always be read as SAI, even if most related research has focused on SAI to date.
Central to any debate on SRM governance should be the topic of justice, along with the role of and impact on the Global South. Beyond the need to avoid exacerbating the existing inequities of climate change, countries in the Global South should be part of the conversation from a procedural perspective. Local expertise in related technologies, consequences, economics, and modeling is necessary to meaningfully engage in SRM deliberations. It will be important that researchers in the Global South—who have essential local context knowledge—are brought into the SRM space and able to shape the evolution of this geoengineering strategy.
More broadly, an indispensable element of any SRM policy is observational data on the state of the atmosphere that’s high quality and shared globally, whether globally coordinated or not. Without good measurement of the impacts, shifts in public perception and government policy will be that much more unpredictable. Moreover, the communication of outlandish narratives should not be discounted. The politicization of Atlantic hurricanes in 2024 is a warning sign for how amenable SRM could be to political distortion and misinformation.
These were just some of the themes that we took away from our recent research workshop. One of our key interests continues to be a consideration of what eventually might drive the emergence of coordinated and noncoordinated deployment scenarios, and what can be done to facilitate more socially beneficial outcomes. Meanwhile, we look forward to continued convenings with members of the social science community who are interested in SRM, and hearing even more from them about their specific interests.
