An influential panel of scientists has recommended the United States pursue a robust research program into solar geoengineering, a suite of techniques that can reflect sunlight and might forestall—temporarily—some of the worst effects of global warming. Such a U.S. program, if supported by the Biden administration, could total $200 million over 5 years, suggests a new report from the National Academies of Sciences, Engineering, and Medicine (NASEM).
Solar geoengineering research could include the deliberate release of substances into the atmosphere, the panel states, but such experiments would require substantial oversight, risk assessment, and public outreach. These small-scale experiments would be intended to study the technical feasibility of these technologies, as well as the environmental and social responses. They should only move forward, the panel said, if they provide observations that could not be recorded by any other means, be it in the lab or by observing natural releases, such as volcanic eruptions. And such experiments should not serve to advance an agenda of larger-scale releases, says Chris Field, a climate scientist at Stanford University and chair of the committee that wrote the report. “Learning more about these technologies shouldn’t be seen as a step toward deployment.”
The report makes clear that no research should occur unless a country has already made strong commitments to deep decarbonization. Reflecting sunlight is at best a bandage and does nothing to curb human-caused emissions of carbon dioxide to the atmosphere—or the ocean acidification that comes with it. Solar geoengineering “only makes sense in the context of a primary societal and government focus on mitigation and adaptation,” says Peter Frumhoff, chief climate scientist at the Union of Concerned Scientists and co-author of the report. “It makes no sense otherwise.”
The current report is welcome news, and aligns with “how we hope to see this research evolve in the future,” says Sarah Doherty, an atmospheric scientist at the University of Washington, Seattle, and program director of the Marine Cloud Brightening Project, which plans within 1 year to test a nozzle that will spray sea salt particles to thicken ocean clouds, reflecting sunlight. “A great deal more research is needed to understand the risks and benefits of climate interventions,” she says.
The report, in preparation since 2019, takes a close look at three proposed solar geoengineering strategies: stratospheric aerosol injection, which would release long-lived reflective particles into the upper atmosphere; marine cloud brightening, which seeks to thicken low-lying clouds over the ocean; and cirrus cloud thinning, which would alter wispy high-altitude ice clouds, allowing more infrared radiation to escape to space. Each has its own risks and uncertainties: Particles released into the stratosphere, home of the ozone layer, are inherently global and long-lived, meaning they could have long-lasting effects. Cloud thickening and thinning, though taking place on more regional scales, rely altering the microphysics of clouds, long the wild card of climate change projections. All of the approaches are worthy of further study, the report says.
While assessing this nascent science, the report spends much of its time laying out a framework for how these programs can be designed and governed. It recommends that the U.S. Global Change Research Program (USGCRP), which coordinates federal climate research from the White House, leads the effort. Any research agenda should include studying the public perception, ethics, political, and socioeconomic trends that could encourage, or stem from, the use of solar geoengineering, the panel wrote. And, if designed right, this research, which would only amount to a few percent of overall climate science funding, should potentially generate results that could persuade regulators to bar certain experiments, Frumhoff says. “They should potentially have outcomes that could say, ‘This is not a good idea.’”
Scientific governance is not a traditional strong suit of USGCRP, which is most well known for producing the quadrennial National Climate Assessment. The report suggests it establish a standing advisory body for solar geoengineering that would include scientists, policymakers, and representatives from civil society to frequently review the program. It also suggests imposing a host of requirements on geoengineering researchers, including adhering to mandatory codes of conduct, creating a public registry of all funded projects, and seeking extensive public engagement.
The $200 million budget suggested by NASEM would be enough to include several aircraft campaigns, though these would not necessarily include any release of particles. However, certain things simply can’t be studied in the lab: for example, how a plume of particles behaves when released by an aircraft. Any such deliberate release would have to clear a high bar mandated in the report. And the panel recommends any such releases be limited to minute amounts, 100 times smaller as the smallest amount that could theoretically influence the environment or global temperature.
Current U.S. research into solar geoengineering is fractured and ad hoc. The last two federal spending bills, for the first time, provided $13 million in total funding to the National Oceanic and Atmospheric Administration to pursue such studies. The agency is planning to fly a lunch-box–size spectrometer on balloon flights in the stratosphere in a bid to capture a high-resolution view of long-lived, light-reflecting particles, with the first flight scheduled later this year. The rest of the money has, so far, gone to improving instrumentation, modeling of the stratosphere, and studies of marine aerosol-cloud interactions, a longstanding research question.
Without a strong U.S. government role, philanthropy has filled the void. Bill Gates has supported a project at Harvard University, called the Stratospheric Controlled Perturbation Experiment (SCoPEx), that is seeking to test its experimental balloon rig, with no injection of particles, above Sweden this year. That proposal is pending before its independent review board, which earlier this year delayed a decision following an outcry from Swedish environmental groups. Meanwhile, last year SilverLining, a nongovernmental organization dedicated to supporting solar geoengineering research, announced $3 million in support to five research labs, largely focused on modeling.
The panel’s recommendation of an integrated research effort is “thrilling,” and its governance recommendations are actionable, incremental, and well-reasoned, says David Keith, a Harvard energy and climate scientist and one of SCoPEx’s lead scientists. But it’s also not the first time an august body has recommended such research, he notes; other bodies have issued similar, though less ambitious, suggestions stretching back to the early 1990s. “The big question,” Keith says, “is will it happen?”