Dimming the Sun to Cool the Planet Is a Desperate Idea, Yet We’re Inching Toward It

The New Yorker
By Bill McKibben


solar-geoengineeringIllustration by Lina Müller

The scientists who study solar geoengineering don’t want anyone to try it. But climate inaction is making it more likely.

If we decide to “solar geoengineer” the Earth—to spray highly reflective particles of a material, such as sulphur, into the stratosphere in order to deflect sunlight and so cool the planet—it will be the second most expansive project that humans have ever undertaken. (The first, obviously, is the ongoing emission of carbon and other heat-trapping gases into the atmosphere.) The idea behind solar geoengineering is essentially to mimic what happens when volcanoes push particles into the atmosphere; a large eruption, such as that of Mt. Pinatubo, in the Philippines, in 1992, can measurably cool the world for a year or two. This scheme, not surprisingly, has few public advocates, and even among those who want to see it studied the inference has been that it would not actually be implemented for decades. “I’m not saying they’ll do it tomorrow,” Dan Schrag, the director of the Harvard University Center for the Environment, who serves on the advisory board of a geoengineering-research project based at the university, told my colleague Elizabeth Kolbert for “Under a White Sky,” her excellent book on technical efforts to repair environmental damage, published last year. “I feel like we might have thirty years,” he said. It’s a number he repeated to me when we met in Cambridge this summer.

Others, around the world, however, are working to speed up that timeline. There are at least three initiatives under way that are studying the potential implementation of solar-radiation management, or S.R.M., as it is sometimes called: a commission under the auspices of the Paris Peace Forum, composed of fifteen current and former global leaders and some environmental and governance experts, that is exploring “policy options” to combat climate change and how these policies might be monitored; a Carnegie Council initiative of how the United Nations might govern geoengineering; and Degrees Initiative, an academic effort based in the United Kingdom and funded by a collection of foundations, that in turn funds research on the effects of such a scheme across the developing world. The result of these initiatives, if not the goal, may be to normalize the idea of geoengineering. It is being taken seriously because of something else that’s speeding up: the horrors that come with an overheating world and now regularly threaten its most densely populated places.

This year, the South Asian subcontinent went through an unprecedented spring heat wave, and then the heat settled, for nearly the entire summer, on China. Drought plagued Europe, while Pakistan endured the worst floods in decades, and the Horn of Africa suffered a fifth consecutive failed rainy season. All this, along with more systemic damage, such as the melt at the poles, happened with a globally averaged temperature increase of just slightly more than one degree Celsius over pre-Industrial Revolution temperatures. To the extent that nations have agreed on anything about climate change, it’s that we need to limit that temperature rise; with the 2016 Paris climate accords, nations adopted a resolution that committed them to “holding the increase in the global average temperature to well below 2° C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5° C above pre-industrial levels.”

The method to accomplish this was supposed to be the reduction of emissions of carbon dioxide and methane by replacing fossil fuels with clean energy. That is happening—indeed, the pace of that transition is quickening perceptibly in the United States, with the adoption of the Biden Administration’s Inflation Reduction Act and its ambitious spending on renewable power. But it’s not happening fast enough: the Intergovernmental Panel on Climate Change has said that we need to cut worldwide emissions in half by 2030, and we’re not on track to come particularly close to that target—in this country or globally. Even before 2030, we may, at least temporarily, pass the 1.5-degree mark. In late September, the longtime NASA scientist James Hansen, who has served as the Paul Revere of global warming, pointed out on his Web site that 2022, like most years in recent decades, will be one of the hottest on record, which is remarkable in this case, because the Pacific is in the grips of a strong La Niña cooling cycle. And the odds are strong, Hansen wrote, that there will be a hot El Niño cycle sometime next year, which means that “2024 is likely to be off the chart as the warmest year on record . . . Even a little futz of an El Nino — like the tropical warming in 2018-19, which barely qualified as an El Nino — should be sufficient for record global temperature. A classical, strong El Nino in 2023-24 could push global temperature to about +1.5°C.”

It’s likely, in other words, that conditions may force a reckoning with the idea of solar geoengineering—of blocking from the Earth some of the sunlight that has always nurtured it. Andy Parker is a British climate researcher who has worked on geoengineering for more than a decade—first at the Royal Society and then at Harvard’s Kennedy School—and now runs the Degrees Initiative. He told me, “For the whole time I’ve worked on this, it’s been like nuclear fusion—always a few decades away no matter when you ask. But there are going to be events in the next decade or so that will sharpen people’s minds. When temperatures approach and then cross 1.5 centigrade, that will be a non-arbitrary moment.” He added, “That’s the first globally agreed climate target we’re on course to break. Unless we find a way to remove carbon in quantities not imaginable presently, this would be the only way to stop or reverse rapidly rising temperature.”

Everyone studying solar geoengineering seems to agree that it’s a terrible thing. “The idea is outlandish,” Parker told me. Mohammed Mofizur Rahman, a Bangladeshi scientist who is one of Degrees Initiatives’ grantees, noted, “It’s crazy stuff.” So did the veteran Hungarian diplomat Janos Pasztor, who runs the Carnegie initiative on geoengineering governance, and said, “People should be suspicious.” Pascal Lamy, a former head of the World Trade Organization (W.T.O.), who is the president of the Paris Peace Forum, agreed, saying, “It would represent a failure.” Jesse Reynolds, a longtime advocate of geoengineering research, who launched the forum’s commission, wrote recently that geoengineering’s “reluctant ‘supporters’ are despondent environmentalists who are concerned about climate change and believe that abatement of greenhouse gas emissions might not be enough.” Reynolds speaks for this geoengineering community on this point. They are, to a person, willing to acknowledge that reducing emissions by replacing coal, gas, and oil represents a much better solution. “I think the basic answer is moving more rapidly out of fossil fuels,” Lamy said. “I’m a European. I’ve been supporting this view for a very long time. Europe is in some ways well ahead of others.”

But these same people all say that, because we’re not making sufficient progress on that task, we’re going to “overshoot” 1.5 degrees Celsius. (The Paris Peace Forum’s project, in fact, is called the Overshoot Commission.) So, they think, we had best investigate and plan for a fallback position: the possibility that the world will need to break the glass and implement this emergency plan. “My own simple answer is that we did not move rapidly enough out of fossil fuels,” Lamy said. Carbon polluters still aren’t paying enough for the harms that they “externalize,” or pass on to everyone else. “And the reason for that, in a global market system which is run by capitalists, whether we like it or not, is that the price of carbon, implicit or explicit, is not at a level that would allow markets to internalize carbon damage.”

Lamy, it must be said, was the head of the W.T.O. from 2005 to 2013, crucial years when CO2 output was soaring, and W.T.O. rules prohibit climate actions that interfere with its free-trade principles. In this country, a large amount of the research and advocacy for these interventions comes from Harvard, the richest educational institution in the world, which only agreed last year, after a decade’s efforts by students and faculty, to phase out fossil-fuel investments in its endowment. Harvard’s research has been funded by, among others, Bill Gates, formerly the richest man in the world. If you wanted to build a conspiracy theory or a science-fiction novel about global élites trying to control the weather, you’d have the pieces. However mixed these groups’ records on addressing climate change have been, they are having an effect now: the pace of publishing studies on geoengineering in scientific journals has begun to pick up, and the National Academies of Sciences, Engineering, and Medicine and other organizations have called for accelerating research. These researchers say that we should be studying both the science and the governance of solar geoengineering, with a focus on two questions: what would happen if we put particles into the stratosphere, and who would make the call?

The enormous step of dimming the sun could turn out to be very easy, at least from a technological point of view. Filling the air with carbon dioxide took close to three hundred years of burning coal and oil and gas, millions of miles of pipelines, thousands of refineries, hundreds of millions of cars. That enormous effort, carried out by just a fraction of the world’s population, has, with increasing speed, pushed the atmospheric concentration of CO2 from about 275 parts per million, before the Industrial Revolution, to about 425 parts per million now. It would take only a tiny fraction of that effort to inject aerosol particles into the stratosphere. (Sulphur dioxide is the most commonly discussed candidate, but aluminum, calcium carbonate, and, most poetically, diamond dust, have also been proposed.) A recent article in the Harvard Environmental Law Review estimates that the “direct costs of deployment—collecting the precursor materials for aerosols, putting them into the sky, monitoring, and so on—would be . . . as low as several billion dollars a year.” Any country with a serious air force could probably release sulphur from planes in the upper atmosphere. You might not even need a country: it would cost Elon Musk, currently the world’s richest man, far less to fund such a mission than it did to buy Twitter—and he’s already got the rockets.

So the question is less whether geoengineering can “work”—as the Harvard Law Review article makes clear, the scientific evidence suggests that it would “likely produce a substantial, rapid cooling effect worldwide” and that it “could also reduce the rate of sea-level rise, sea-ice loss, heatwaves, extreme weather, and climate change-associated anomalies in the water cycle.” The question is more: what else would it do? On a global scale it could, at least temporarily, turn the sky hazy or milky (hence the title of Kolbert’s book); it could alter “the quality of the light plants use for photosynthesis” (no small thing on a planet basically built on chlorophyll—studies have shown that U.S. corn production increased as polluting aerosols went down in the wake of amendments to the Clean Air Act); and it might damage the ozone layer, which is only now repairing itself from our recent assault with fluorocarbons. (By way of comparison, the largest volcanic eruption ever recorded, at Mt. Tambora, in 1815, on an island that is now part of Indonesia, spewed a cloud of particles that temporarily caused the temperature to drop a degree Celsius. That change produced, in 1816, “a year without a summer” across much of the northern hemisphere. Lake ice was observed in Pennsylvania into August, and, in Europe, where grain yields plummeted, hungry crowds rioted beneath banners reading “Bread or Blood.”)

The most likely problems, though, would probably be not global but regional. Lowering the temperature, precisely because it would affect global weather patterns, would produce different and hard-to-predict outcomes in different places. I spoke about this tendency with Inés Camilloni, a climatologist at the University of Buenos Aires who is investigating the possible effects of geoengineering on rivers in South America’s La Plata river basin. (Her work is partially funded by the Degrees Initiative.) “What we found is that implementation of S.R.M. strategies could lead to an increase in the mean flow of the rivers of the basin, which means more water for hydropower energy, something that could be considered positive. Also an increase in the levels at low-flow times, which is a positive, considering these droughts we’re having,” she said. “But you also could experience an increase in the higher flow, and this could be associated in the rate of flooding in the rivers.”

In South Africa, a study by a University of Cape Town team, also funded by Parker’s group, indicated that S.R.M. could cut the possibility of drought in that coastal city, which, in 2018, came dangerously close to reaching a “day zero” shutoff of water supplies, as local reservoirs turned into dustbowls. But another team working from Benin, in West Africa, found that geoengineering would likely lead to less rain in a region that has suffered from calamitous desertification. Mohammed Rahman, working from an office in Bangladesh’s renowned International Centre for Diarrhoeal Disease Research, said his research showed that in some parts of Asia malaria would increase, and in others it would decline. “The result we had was on a coarse scale, like a continental scale. Here it gets better, here it gets worse,” he said.

A climate “solution” that helps some and harms others could spark its own kind of crisis. A Brookings Institution report last December began with a scenario—it’s 2035, and a country begins unilateral deployment of S.R.M.: “the country has decided that it can no longer wait; they see geoengineering as their only option.” Initially, “the decision seems wise, as the increase in global temperatures starts to level off. But soon other types of anomalous weather begin to appear: unexpected and severe droughts hit countries around the world, disrupting agriculture.” In response, “another large country, under the impression it has been severely harmed . . . carries out a focused military strike against the geoengineering equipment, a decision supported by other nations who also believe they have been negatively impacted.” This development, however, becomes even more devastating—with no one putting chemicals into the stratosphere, they decline rapidly in the course of a year, and “temperatures dramatically rebound to the levels they would have reached on their previous trajectory.” The result, they conclude, is “disastrous.”

That last potential development, which scientists call “termination shock,” has been widely researched; Raymond Pierrehumbert, a professor of physics at the University of Oxford, and Michael Mann, perhaps America’s best-known climate scientist after Hansen, have said that it is reason enough to avoid solar geoengineering. “Some proponents insist we can always stop if we don’t like the result,” Mann and Pierrehumbert wrote in the Guardian. “Well yes, we can stop. Just like if you’re being kept alive by a ventilator with no hope of a cure, you can turn it off — and suffer the consequences.” The other projected problem, though—the chance for huge differential effects—is the one that could keep the discussion from ever really getting off the ground. The peril isn’t that far-fetched; volcanic eruptions have affected the timing and the position of the monsoon on the South Asian subcontinent. Imagine if India started pumping sulphur into the atmosphere only to see a huge drought hit Pakistan: two nuclear powers, already at odds, with one convinced the other is harming its people. Or maybe it’s China—driven by a series of summers like the one it just endured—that starts down this road, and it’s India that suddenly faces unrelenting floods. These two nations also share a militarized border, and a series of overlapping international alliances. Or maybe it’s Russia, or any number of countries. Global treaties prohibit weather modification as a tool of war (something that the U.S., in fact, attempted in Vietnam, but at present they don’t rule out war as a reaction to weather modification gone awry.

All this explains why, earlier this year, sixty “senior scholars” from across the world, now joined altogether by more than three hundred and fifty political and physical scientists, signed a letter urging an absolute moratorium—“an international non-use agreement”—on solar geoengineering. Frank Biermann, a political scientist at Utrecht University, in the Netherlands, was a core organizer. “We believe there’s no governance system existing that could decide this, and that none is plausible,” he told me. “You’d have to take decisions on duration, on the degree—and if there are conflicts—‘we want a little more here, a little less here’—all these need adjudication.” He points out that the U.N. Security Council would be a problematic governing body: “Anything can be blocked by the veto of five of the most polluting countries. Some kind of governance by the major powers? You’d need the agreement of the U.S., Russia, China, India, and there’s no chance of that. The small countries? The people who want this talk about consultation, but not co-decision. When I talk to African colleagues, none of them expects the world would get a decision right for their countries.” Faced with such problems, Biermann and his colleagues urge a complete halt to any testing of the new technologies. “Governance has to be first,” he said. “If you don’t know what to do with such technology, don’t develop it.”


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