National Academies urge U.S. to study artificial cooling

By Chelsea Harvey | 03/26/2021 06:58 AM EDT

The controversial idea of lowering temperatures by altering the atmosphere should be studied by the U.S. government, top scientists say. The recommendation has detractors.

Green wisps of the aurora australis are seen near the Earth's airglow as the International Space Station orbits above the Indian Ocean. Researchers are advancing their understanding of solar geoengineering as one potential way to lessen the impacts of climate change.

Green wisps of the aurora australis are seen near the Earth's airglow as the International Space Station orbits above the Indian Ocean. Researchers are advancing their understanding of solar geoengineering as one potential way to lessen the impacts of climate change. NASA

A controversial policy to address climate change by artificially cooling the planet deserves more research, according to a panel of leading U.S. scientists.

But only if it is carefully governed.

That’s the major conclusion from a report on solar geoengineering released yesterday by the National Academies of Sciences, Engineering and Medicine. The report recommends that the federal government invest up to $200 million over the next five years to develop a national research program.


Solar geoengineering refers to a kind of climate engineering aimed at cooling the planet by reflecting sunlight away from the Earth and back out to space. So far, it’s a purely hypothetical idea — but scientists have proposed a number of ways it could be done.

The most common proposal suggests spraying reflective aerosols into the atmosphere, where they would beam sunlight away from the Earth. Other proposals involve making clouds brighter by injecting them with particles, or to help trap less heat beneath them.

They’re contentious ideas. Experts have many concerns about the possibility of unintended consequences, such as unwanted effects on rainfall or other global weather patterns.

Furthermore, solar geoengineering doesn’t address the root cause of climate change — greenhouse gas emissions. It simply masks their warming effect on the planet. There are consequences of rising carbon dioxide levels, such as ocean acidification, that geoengineering can’t address.

There is also the question of whether humans, and Earth, could become dependent on geoengineering. These practices, if begun, could become virtually impossible to stop if emissions continue to rise. Doing so could cause temperatures to skyrocket, according to some researchers.

More broadly, some critics have expressed concern that a focus on solar geoengineering could distract policymakers from reducing greenhouse gases.

With that collage of worries in the background, the National Academies advocated continued research — but in a carefully controlled way, with an emphasis on governance, international cooperation and social concerns.

"At this point, it is clear that solar geoengineering is not a substitute for reducing greenhouse gas emissions," Stanford University researcher Chris Field, chair of the committee that wrote the report, said at a webinar announcing the recommendations. "To the extent that it’s considered at all, it should only be considered as a complement to other efforts to reduce greenhouse gas emissions."

At the moment, emissions are not falling quickly enough to meet the goals of the Paris Agreement and to avoid dangerous levels of future warming. That means policymakers should keep exploring additional options for addressing climate change, the report said.

The committee doesn’t advocate for or against solar geoengineering as a future climate tool, Field cautioned. It suggests that there isn’t enough information at the moment to make those kinds of decisions. That’s where continued research will be useful.

The report calls for a national research program housed under the U.S. Global Change Research Program, which coordinates climate research across federal agencies.

This program should focus on several broad spheres, the report says. These include scientific and technical questions about the physical effects of solar geoengineering, as well as social concerns and questions related to governance and regulation, on both a domestic and an international scale.

Governance questions are a growing concern among researchers. With so many scientific uncertainties and potential risks, experts highlight the need for international frameworks to regulate geoengineering experiments and negotiate agreements about how — if ever — solar geoengineering should be deployed.

The report also offers recommendations for future experiments. To date, geoengineering research has consisted almost entirely of modeling studies.

But that could change soon.

A Harvard University project dubbed SCoPEx — short for Stratospheric Controlled Perturbation Experiment — is planning some of the world’s first geoengineering field experiments. The project aims to send a high-altitude balloon up to the stratosphere, where it will release small quantities of mineral dust into the air.

These experiments could help scientists better understand how aerosols behave high up in the atmosphere.

SCoPEx researchers have repeatedly emphasized that the project is small in scale, and that any aerosols it uses will be environmentally safe and released in small quantities. Still, the project has incited controversy among environmental groups, highlighting the many social concerns still swirling around solar geoengineering (Climatewire, March 9).

The National Academies report recommends keeping these kinds of social concerns central to any national research program.

"A lot of the emphasis on the design of the research program is to make sure that there are pathways for hearing from diverse communities around the world, communities that can express their preferences about the design of the research, the goals of the research, the prioritization of different kinds of outcomes," Field said yesterday.

Still, some experts have reservations about the new recommendations.

Prakash Kashwan, a political scientist at the University of Connecticut, said he felt the report could have better emphasized the seriousness of some concerns over others. Uncertainties about the impacts of solar geoengineering on global weather patterns have the potential to affect some regions of the world more severely than others, he pointed out.

Some experts have raised concerns about potential effects of geoengineering on monsoon rainfall in parts of Asia and Africa, he said. More than 2 billion people around the world rely on these rainfall patterns to support their water and agricultural needs. These kinds of issues should be given special weight, Kashwan suggested.

"Some uncertainties are much more highly consequential for the global society, and especially for the poor and vulnerable," he told E&E News.

Kashwan also reiterated concerns about potential political effects. While the report makes clear that geoengineering is not a substitute for climate mitigation, he suggests that this doesn’t necessarily prevent policymakers from using it in that way.

"The problem is the extent to which researchers are really helpless in deciding how research is used in the political system," he said. "That part has yet to be fully appreciated."

Kashwan suggests that more dialogue might be warranted before funding a national research program, with greater input from both the international community and political experts who can weigh in on the ways that geoengineering research might affect political decisions.

Still, members of the National Academies committee say that these kinds of concerns were central to their thinking when designing their recommendations.

"There has been some social science research trying to figure out whether research on solar geoengineering is likely to deter investment in mitigation," Marion Hourdequin, a committee member and philosophy professor at Colorado College, said at yesterday’s webinar, adding that she thinks "the jury’s sort of still out."

In light of those concerns, she said, the recommendations attempted to outline a modestly funded program that emphasizes the importance of reducing greenhouse gas emissions and that engages with diverse communities about their concerns along the way.

"Part of the work of the research program will be to continue to think about how program design can be refined in ways that ensure that decarbonization remains central," she said.