Should Solar Geoengineering Be a Tool to Slow Global Warming, or is Manipulating the Atmosphere Too Dangerous?

A new National Academies report is focusing attention on the controversial possibility of cooling the climate by reflecting sunlight away from Earth.

The sun starts to rise behind Britain's largest offshore wind farm on July 19, 2006 in Norfolk, England. Credit: Matt Cardy/Getty Images
GREAT YARMOUTH, ENGLAND - JULY 19: The sun starts to rise behind Britain's largest offshore wind farm off the Great Yarmouth coastline on July 19, 2006 in Norfolk, England. The 30 turbines cost GBP75million and can generate enough power for 41,000 homes are seen by supporters as a clean and green way to generate electricity and a way of cutting down on harmful green house gas emmissions. (Photo by Matt Cardy/Getty Images)

Share this article

The risks of the climate crisis are so urgent that the United States, in cooperation with other countries and under strict rules, should study the possibility of temporarily cooling the planet through solar geoengineering, a report released Thursday by the National Academies of Sciences, Engineering and Medicine says.

The report focuses on adding reflective particles to the upper atmosphere to bounce the sun’s heat back to space, brightening low-altitude clouds over the ocean to make them more reflective or thinning wispy cirrus clouds so that they trap less heat on the surface of the planet. 

Supporting research into those possibilities shouldn’t be equated with actually implementing them, the NAS committee members involved with the report emphasized, adding that such studies should not detract from the need to cut greenhouse gas emissions. And scientists “need to be open to terminating” geoengineering research if findings indicate that such manipulations of the atmosphere would carry undue risk of dangerous consequences, they said.

“It’s kind of surreal to even be talking about this,” said Ambuj Sagar, who studies science and technology policy at the Indian Institute of Technology, Delhi, and was part of the committee that compiled the report. “You can’t be doing climate policy without thinking about geoengineering, and the more you get into it, the more complex it is. It raises all kinds of issues with international politics and governance.”


We deliver climate news to your inbox like nobody else. Every day or once a week, our original stories and digest of the web’s top headlines deliver the full story, for free.

But if greenhouse gas emissions don’t start dropping fast, people in 10 or 20 years will need sound science to decide if they want to pull the solar engineering emergency brake, said Peter Irvine, who studies solar geoengineering at University College London and was not involved in the new report.

The Academies’ report recommends a research budget of $100 million to $200 million for the next five years, as a “minor part of the overall U.S. research portfolio related to climate change.” For now, it says, research should not be focused on a path toward deployment, but on understanding how solar geoengineering fits with all the options for responding to climate change. 

Solar geoengineering only makes sense in tandem with cutting emissions, because solar geoengineering doesn’t actually address the buildup of greenhouse gases that warms the climate. It only masks some of the symptoms for as long as the measures are active. Temperatures would rebound dangerously fast when atmospheric manipulation ends. A 2015 report from the Academies concluded that geoengineering is no substitute for emissions reductions, and that none of the proposed interventions are ready for deployment.

“Even the question of whether to do research is complex,” Sagar said. “Who has the right to decide how to move on this?” 

Since any implementation of solar geoengineering could have unintended consequences, it’s critical that everyone who could be affected has a seat at the table where its use is discussed, he said.

Can Climate Hacking Save the Planet?

Doing research on solar radiation management isn’t advocating for it, said Helene Muri, who studies geoengineering with the Industrial Ecology Programme at the Norwegian University of Science and Technology in Oslo.

“A lot of people who are doing the research aren’t endorsing it,” she said. A recent study she worked on, published March 11 in Earth System Dynamics, showed that solar radiation management could have potentially unexpected effects on the way soils and plants process carbon dioxide, partly because plants and microbes respond differently to direct and filtered light.

Marcia McNutt, president of the National Academy of Sciences, said that, when it comes to solar geoengineering, researchers need to engage with the public “to ask not just can we, but should we,” in a way similar to the ongoing discussions in fields such as artificial intelligence or gene editing. Basic questions about governance, like who is involved in making decisions, are just as important as scientific and technical information when it comes to deciding if, when, where and for how long geoengineering might ultimately be used “to mask global warming,” she said.

The report suggests that the U.S. Global Change Research Program should guide the effort. Its focus should be the context and goals of the research, including strategies for decision-making and engaging all countries on the issue; impacts and technical dimensions, such as how the reflective particles act in the atmosphere and affect ecological systems; and social aspects, including public perceptions and engagement, along with justice, ethics and equity considerations. 

Last Chance, or Icarus Moment?

The topic of geoengineering has surfaced with increasing frequency in recent years. A few months ago, scientists with the National Oceanic and Atmospheric Administration said their latest budget included $4 million to study what they called a “Plan B” for climate change. In 2013, NBC and others reported that U.S. intelligence agencies helped fund a previous National Academy of Sciences study assessing geoengineering risks. 

Most recently, an experiment called SCoPEx, led by the Keutsch Group at Harvard and planned for June in the sky above Sweden, has been portrayed both as a crucial step toward better understanding solar geoengineering, or as a dangerous slip down a slope leading to a potential Icarus moment for humanity, with the illusion of control over nature ending in a fiery crash.

The first step of SCoPEx is to launch a balloon to test instruments that could be used to measure how reflective particles work in a small area and affect the adjacent atmosphere. 

Even that small step is worrisome, said Linda Schneider, of the Heinrich Böll Foundation, a nonprofit group with ties to the German Green Party.

“What civil society currently is worried about is that the new NAS report will be used to legitimize Harvard’s SCoPEx project,” she said. “It’s notable how the first thing they highlight is the need for a massive expansion of research. We maintain that it is an untestable technology and the real impacts and consequences would only be felt once the technology would actually be deployed, and then there is no going back.”

Last week, the Saami Council, representing Indigenous communities in Sweden, Finland, Russia and Norway, wrote a letter to the SCoPEx advisory committee demanding cancellation of the balloon experiment because there was a lack of transparency, inclusivity and engagement in the planning process.

Keep Environmental Journalism Alive

ICN provides award-winning climate coverage free of charge and advertising. We rely on donations from readers like you to keep going.

Donate Now

Approving research incrementally could create unjustified legitimacy for geoengineering and make the technology seem palatable, Schneider cautioned, enabling a slide from “small, seemingly benign equipment testing to larger-scale experimentation with particle release.” 

“We think that solar radiation management comes with so many known and unknown existential risks for communities and ecosystems that it is too dangerous to ever be developed, and should instead be banned outright,” she said.

Tinkering with the reflectivity of the atmosphere is a “bad idea whose time has come,” Oxford physics Professor Raymond Pierrehumbert wrote for the Bulletin of Atomic Scientists back in 2017, commenting on ideas like brightening clouds to save the Great Barrier Reef in Australia. The new report from the Academies could be used as a “crutch for polluters” to further delay climate action, said Penn State climate researcher Michael Mann

A broad global coalition of civic groups called for a geoengineering ban in 2019 during a meeting of the United Nations Environmental Programme, when an early Swiss proposal to consider global governance of such interventions was rejected based in part on objections from the United States and Saudi Arabia.

Globally, environmental groups track climate hacking efforts via the geoengineering monitor, which provides valuable information on relatively unknown geoengineering ideas like covering big tracts of land in Africa with plastic to reflect heat, and oundation-funded solar geoengineering research in Africa.

Could Small Experiments Bring a Cascade of Climate Interventions?

Some of the skepticism is warranted, said Harvard climate economist Gernot Wagner, the founding co-director of Harvard’s solar geoengineering research program, which launched the SCoPEx project.

Wagner, who left the geoengineering program in 2019, said that, as a social scientist, he understands that the complexity of geoengineering can “lead to hesitation, which is understandable and laudable.” The focus on research and the regulation of the research, rather than deployment, is “where the conversation should be,” he said, adding that, “if anything, there should be a firm moratorium” on deployment.

The level of funding proposed in the National Academies report is about equal to the total current global spending on geoengineering research, and not much compared to overall spending on climate science, on which the United States Global Change Research Program spends about $3 billion annually, he said.

“It concludes, in very reasonable language, that careful outdoor small-scale experiments are OK. A lot of learning can happen from those experiments. The SCoPEx seems to meet these criteria,” he said, explaining that the project’s advisory committee is still deliberating on whether to give it the final go-ahead.

Small geoengineering research projects and experiments should also be considered in the context of related research, including efforts to understand how emissions from volcanoes, wildfires and diesel-burning ships affect the climate, he said. A second stage of the SCoPEx experiment would involve fewer particles than those emitted by a plane’s jet engines during one minute of commercial flight, he said.

Irvine, the University College London researcher, said the new report echoes similar recommendations made by the United Kingdom’s Royal Academy in 2009. 

“It’s deliberately not about how do we go about building the equipment,” he said, but focused on “foundational science, including the social and ethical dimensions, as well as promoting an international governance structure.”

Focusing on internationally regulated and government-financed research could dispel the “James Bond-villainesque” perception of geoengineering, especially since most of the current funding comes from billionaire philanthropists, he added.

Emissions are rising at a rate that would push the global average temperature up by between 4.5 degrees and 5.5 degrees Fahrenheit, which will result in serious impacts to people and ecosystems. 

“The possibility of minimizing some of those harms (with solar geoengineering) might seem new, radical and tempting, but should not distract from the urgency of cutting greenhouse gas emissions,” he said. 

One of the fears of not researching and establishing governance for geoengineering is that “growing and powerful nations like Indonesia or India, nations that are at the sharper end of climate change,” might resort to geoengineering unilaterally, potentially provoking regional impacts or even conflict, he added.

Irvine said that, based on the science of the past decade, he thinks it’s likely that solar geoengineering, especially at the stratospheric level, could substantially reduce some climate risks in some areas, while potentially increasing them elsewhere in unexpected ways. That could lead down a path requiring constant human attempts to manipulate the climate system. 

“Is this a world we want, where we have to alter the Earth’s energy budget for decades?” he asked.