Skip to content Skip to navigation

U.S. Should Cautiously Pursue Solar Geoengineering Research

Mar 25, 2021


Given the urgency of the risks posed by climate change, the U.S. should pursue a research program for solar geoengineering – in coordination with other nations, subject to governance, and alongside a robust portfolio of climate mitigation and adaptation policies, says a new report from the National Academies of Sciences, Engineering, and Medicine. Written by a committee chaired by Perry L. McCarty Director of the Stanford Woods Institute for the Environment Chris Field, the report emphasizes that solar geoengineering is not a substitute for reducing greenhouse gas emissions.

Solar geoengineering refers to strategies designed to cool Earth either by adding small reflective particles to the upper atmosphere, by increasing reflective cloud cover in the lower atmosphere, or by thinning high-altitude clouds that can absorb heat. While such strategies have the potential to reduce global temperatures and thereby ameliorate some of the risks posed by climate change, they could also introduce an array of unknown or negative consequences, says Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance.

A U.S. solar geoengineering research program should aim to enhance policymakers’ understanding of climate response options.  The research should work to better understand solar geoengineering’s technical feasibility, possible impacts on society and the environment, public perceptions, and potential social responses — but it should not be designed to advance future deployment of these interventions. Scientific understanding of many aspects of solar geoengineering technologies remains limited, including how they could affect weather extremes, agriculture, natural ecosystems, or human health. There currently is no coordinated national effort for solar geoengineering research.  

The report recommends a comprehensive plan for governing solar geoengineering research, designed to ensure it moves forward in a socially responsible manner. Researchers should follow a code of conduct, for example, and research should be catalogued in a public registry, be subject to regular program assessment and review, and allow for public engagement. 

Deliberate outdoor experiments that involve releasing substances into the atmosphere should be considered only when they can provide critical observations that cannot be provided by laboratory study, modeling, or experiments of opportunity — such as volcanic eruptions. Outdoor experiments should be subject to appropriate governance including permitting and impact assessments, says the report.

“The U.S. solar geoengineering research program should be all about helping society make more informed decisions,” said Field. “As we continue to make slow progress in addressing climate change, we urgently need to understand the full range of options for alleviating its harms. Based on all of the evidence from social science, natural science, and technology — this research program could either indicate that solar geoengineering should not be considered further, or conclude that it warrants additional effort.”

Research Priorities

The report says the U.S. Global Change Research Program (USGCRP) should lead the effort to establish and coordinate a solar geoengineering research program across federal agencies and scientific disciplines, with funding in the range of $100 million-$200 million over the first five years. USGCRP would enable oversight and governance of research activities, including ensuring peer review, coordinating budget proposals and requests, periodically assessing progress, and defining program goals. Funding should be set aside specifically for implementation of governance and public engagement efforts.

The research agenda should encompass 13 specific areas of research, which can be grouped into the following three broad areas of investigation: 

  • Context and goals for solar geoengineering research, including research on the goals and social context for solar geoengineering research, developing modeling scenarios, strategies for decision-making under uncertainty, and the capacity needed for all countries to engage meaningfully on this issue.
  • Impacts and technical dimensions, including the properties of injected reflective particles and their interactions with clouds and atmospheric processes, possible climate outcomes and subsequent impacts on ecological and societal systems, technical requirements for advancing these technologies, and advancing monitoring and attribution capabilities.
  • Social dimensions, including research on public perceptions of and engagement with solar geoengineering; domestic and international conflict and cooperation; effective governance of solar geoengineering; and integration of justice, ethics, and equity considerations.

“For solar geoengineering, there are many unanswered scientific questions that address risks and unintended consequences, but equally important are the governance questions of who will decide and how long to deploy this intervention to mask global warming,” said Marcia McNutt, president of the National Academy of Sciences, and committee chair of the 2015 National Academies report Climate Intervention: Reflecting Sunlight to Cool Earth. “Given the urgency of the climate crisis, solar geoengineering needs to be studied further. But just as with advances in fields such as artificial intelligence or gene editing, science needs to engage the public to ask not just can we, but should we?”

Research Governance

Careful governance will be critical for enabling solar geoengineering research to proceed. The report recommends governance mechanisms for solar geoengineering research that include roles for government, universities, independent institutions, research teams, and other nations.

The report also recommends that the U.S. support the development of international governance mechanisms, but notes robust international governance practices and institutions will likely emerge only after more countries commit to engage with this research. The report calls for promoting international partnerships — which should include participation from populations that have been historically underrepresented in global decision-making — within research teams, an international registry of solar geoengineering research, and thorough information sharing and cooperation. An ad-hoc working group under the auspices of the United Nations General Assembly or another international body should be created to address future governance needs for solar geoengineering research.   

The report says domestic and international governance of solar geoengineering can develop simultaneously, informing and strengthening each other, and that international cooperation among researchers can still develop in the absence of formal governance. 

The study — undertaken by the Committee on Developing a Research Agenda and Research Governance Approaches for Climate Intervention Strategies That Reflect Sunlight to Cool Earth — was sponsored by the Band Foundation, U.S. Department of Energy, National Academy of Sciences’ Arthur L. Day Fund, National Oceanic and Atmospheric Administration, Christopher Reynolds Foundation, John D. and Catherine T. MacArthur Foundation, National Aeronautics and Space Administration, and V. Kann Rasmussen Foundation.  The National Academies of Sciences, Engineering, and Medicine are private, nonprofit institutions that provide independent, objective analysis and advice to the nation to solve complex problems and inform public policy decisions related to science, technology, and medicine. They operate under an 1863 congressional charter to the National Academy of Sciences, signed by President Lincoln.

Illustration of stratospheric aerosol injection, marine cloud brightening, and cirrus cloud

thinning — the three solar geoengineering interventions considered in the report. (credit: NAS)

Original press release:

Contact Information

Christine H. Black
Associate Director, Communications

Devon Ryan
Communications Manager

Rob Jordan
Editor / Senior Writer