scorecardresearch Skip to main content

When it comes to solar geoengineering, we’re still very much in the dark

It’s a misguided bid for a quick fix to the climate crisis that might hold off the symptoms of global warming without confronting the necessary task of kicking the world’s fossil fuel habit.

Air pollution rises from cooling towers at a lignite fired power plant in Germany.Bloomberg Creative Photos/Photographer: Bloomberg Creative

The climate crisis provides ample grounds for panic. While the “12 years to Doomsday” rhetoric is off the mark, since there is no single threshold at which all catastrophes suddenly break loose, each year that we continue to pump carbon dioxide into the atmosphere irreversibly ratchets up warming and takes us deeper into the danger zone. Panic, however justifiable, can make for foolish decisions. Among the most foolish proposals is cooling the planet by spewing substances into the upper atmosphere that would reflect sunlight back to space. It’s a misguided bid for a quick fix that might hold off the symptoms of global warming without the need to confront the challenging and necessary task of kicking the world’s fossil fuel habit.

Proponents call the quick fix “solar geoengineering,” but others prefer the term “climate intervention,” in recognition of the fact that we don’t know nearly enough about the response of the climate system to justify calling it “engineering,” which conveys a sense of precise, predictable control. What could possibly go wrong?


Well, there are many problems with the scheme, but the real showstopper is that the carbon dioxide released by fossil fuel burning — the chief cause of the climate crisis — persists in the atmosphere for thousands of years. In contrast, the particles created by solar climate interventions fall out of the sky after just a year or so.

If we ever got into a state where we rely on solar climate intervention to prevent catastrophe, it would have to be continued without fail year after year, for 1,000 years or more — lest the termination shock from cessation of the intervention unleash pent-up global warming that would fry the planet in a matter of decades. Solar climate intervention is sometimes described as a “Plan B” for the climate crisis — something that should be ready to roll out in case the world fails to restrain carbon dioxide emissions. Nothing could be further from the truth.


If carbon dioxide emissions continue unabated, each year more of that carbon dioxide will build up in the atmosphere. That means, each year, the level of climate intervention must be ratcheted up, leading to a death spiral of ever-increasing pent-up warming held precariously in check by ever greater intensity of climate intervention. The disastrous consequences of termination shock would grow as we cower year after year under the flimsy stratospheric sunshade, hoping that technology to suck carbon dioxide out of the atmosphere on a massive scale becomes practical before disaster strikes.

What is on the table now is “just research,” but that doesn’t make it less of a threat. Any research involving building apparatus for injecting aerosol-forming substances into the upper atmosphere inevitably develops technology that paves the way for deployment. That includes Harvard’s shovel-ready SCOPEX field experiment program. When have human societies ever developed a technology and left it on the shelf? Once nerve gas and hydrogen bombs were also “just research.” Proponents say the technology should be developed “just in case,” but in case of what?

The push for research is getting out ahead of any clear articulation of the circumstances, if any, in which the technology could make a safe and necessary contribution to addressing climate change, and how it might be governed if deployed. It has been argued that we should research the technology in case some rogue nation tries it out, but this risks developing the very technology that makes such a scenario more likely. And, given the current political environment, we can’t discount that the United States itself might wind up being that rogue nation.


After years of scientific research being kept alive on life support by private donors, there are ominous signs that the push for a major government-funded program is gaining traction in the United States. During reconciliation of this year’s budget bill, in December 2019, a phrase was inserted into a formerly innocuous appropriation provision for the National Oceanographic and Atmospheric Administration that would authorize NOAA to spend up to $4 million on solar climate intervention research — including research involving field experimentation.

On the heels of that, Democratic Representative Jerry McNerney of California introduced the Climate Intervention Research Act, which would open the floodgates by redefining the mission of NOAA to explicitly include solar climate intervention. David Fahey, director of the Chemical Sciences Division of NOAA’s Earth System Research Laboratory, is an enthusiastic supporter of the act. He sees $100 million of federal funding flowing into solar climate intervention research and development if the bill passes. In a bizarre turn of events, the Democratic Climate Action Plan includes McNerney’s bill as an action item among its several hundred pages of generally worthy plans to address the climate crisis.


This anomaly should not be allowed to sully an otherwise thrilling plan. Anybody hoping for constructive action on global warming should hope fervently for a Democratic victory in the White House and Senate, since today’s Republican Party is unwilling to confront the climate crisis or even admit that there’s a problem. If only half the measures in the Action Plan make it into law, it will be a big step forward — however, McNerney’s bill should not be among them.

Once the technology is developed, the decision on whether to deploy will be taken out of the hands of the scientists who understand the consequences. Solar climate intervention could conceivably safely make a marginal contribution to climate recovery once we are well on the way to achieving net-zero carbon dioxide emissions. But even that would assume a very different world than we now live in, one with utmost respect for science in making decisions affecting humanity and for international norms of cooperation. A world where the leader of the world’s most powerful nation thinks drinking bleach might be a way to cure COVID-19 is not that world.

Regardless of the outcome of the November election, the polarization and authoritarian currents plaguing politics in the United States and many other nations will remain. This is not a world in which we should risk unleashing a technology as dangerous and destabilizing as solar climate intervention.

Raymond T. Pierrehumbert is the Halley Professor of Physics at the University of Oxford, a member of the Bulletin of the Atomic Scientists Science and Security board, and a fellow of the Royal Society of London. He was a coauthor of the US National Academy report on climate interventions and a lead author on the Third Assessment Report of the Intergovernmental Panel on Climate Change.