Could solar geoengineering reduce human suffering?

Solar geoengineering is in drastic need of rebranding.

The impacts of climate change continue to grow clearer and more dire, while countries backslide on plans to wean off fossil fuels and cut greenhouse gas emissions to prevent the worst effects of warming. All that has raised the profile of solar geoengineering: the controversial, and still theoretical, method of cooling the planet by injecting tiny aerosol particles into the stratosphere to reflect more of the sun’s energy back into space.

The technology is often discussed in the public and the media in terms of its most obvious effect: a modest but immediate reduction in global average temperature, which could help limit climate damage while humanity works to zero out its greenhouse gas emissions. But that common framing often fails to make clear that this temporary technofix — which depends on adding more unnatural pollution to the skies — could also reduce human suffering as the world seeks to stabilize the climate.

Call it the world’s biggest trolley problem. The benefits would almost certainly be spread unevenly around the planet, and solar geoengineering could worsen conditions in some places even if it cuts down on suffering overall. But steering that stale conversation over geoengineering directly into this ethical hornets’ nest may provide some more clarity to a field that has been rehashing the same arguments for two decades.

“Reframing it as a humanitarian intervention would certainly change the debate,” said New York University professor and climate economist Gernot Wagner during a recent Harvard University seminar on the ethics of geoengineering. “Yes, of course this is about being a humanitarian, in the all-encompassing sense of the term.”

Think of it this way: Between now and 2050, or 2070, or 2100, there is some total amount of human suffering in the form of hunger and illness and premature death. We’ll call that amount X. If the world deployed solar geoengineering, it would likely lower global temperatures, shift precipitation and disaster patterns, alter crop yields, and do other things to produce a different total — call it Y. If Y is less than X, there is an obvious moral imperative to choose the path with less suffering.

Emissions cuts are not enough

“The main motivation behind it would be dealing with short-term suffering that can’t be mitigated through any other means,” said Kate Ricke, a climate scientist at the University of California, San Diego, who has been involved with geoengineering modeling research. “Climate change is already causing a lot of damages and suffering, and there’s just no way to reduce the climate change that’s already happening as quickly as solar geoengineering might be able to.”

Governments can throw money at climate adaptation, but that simply won’t protect everyone from increasingly devastating heat waves, crop losses and more, especially in the poorer parts of the world. Every new climate report makes it more and more clear: The impacts are here, now, and getting worse with every ton of CO2 humans send skyward.

The climate system’s inertia adds another wrinkle. Let’s say humanity really did manage to stop emitting greenhouse gases by 2050, which the U.N. says would give humanity the best chance of avoiding severe and irreversible climate impacts over the long term. But zeroing out climate-change-causing emissions themselves is not enough to eliminate the suffering that would result from the heat-trapping gases produced up until 2050. Carbon dioxide stays in the atmosphere for centuries, and much warming — and associated sea level rise, weather changes and more — are baked into the system for far beyond any point where we would entirely abandon fossil fuels.

A recent U.N. climate report, released in late February, highlighted the additional problem of “overshoot” — if the temperature soars past the threshold of 1.5 degrees Celsius (2.7 degrees Fahrenheit) over preindustrial levels, some of the impacts are permanent. Even if the heat is turned back down in subsequent years, you can’t get back some of the ice sheets, coral reefs and other ecosystems humans depend on.

“If you want to absolutely reduce the amount of suffering from climate [change], you have to do something beyond emissions cuts,” said David Keith, a Harvard physics professor who has for more than a decade been the most publicly prominent solar geoengineering researcher and is among those trying to navigate a rocky path toward the first physical experiments of the technology.

The potential to prevent suffering, disease and death on an unknown but potentially wide scale in the face of those inertial problems, some experts say, makes it worth considering and researching — and talking about — solar geoengineering’s potential as quickly as possible.

Winners and losers

Of course, using this framework for decision-making requires that we can reliably quantify the amount of climate-change-related suffering with and without solar geoengineering. One of the criticisms of the technology — which is also known as solar radiation management or SRM — is that there are too many “unknown unknowns,” potential unforeseen problems with theoretically catastrophic consequences given the approach’s necessarily global scope.

As the science historian James Fleming has written, “Global climate engineering is untested and untestable, and dangerous beyond belief.” It may be technically “untestable” because an actual test would be equivalent to deployment at global scale, but computer modeling studies have started to make serious dents in the issue, and major institutions such as the National Academies of Sciences, Engineering and Medicine have issued calls to expand and formalize such research programs.

“I don’t think there’s a single equation” for suffering, Ricke said. But there is plenty of modeling research, which in principle is quite similar to that done for climate change itself, to try teasing out impacts in a geoengineered world versus a non-geoengineered world. In both cases, models are tasked with projecting how adding pollution to the atmosphere alters the temperature of Earth’s atmosphere, oceans and land.

A study published last summer showed that SRM would offer increased global yields of corn, wheat, rice and three other staple crops when compared with only emissions reductions. Another from 2019 found increased rice yields specifically in China with SRM and a middle-of-the-road warming scenario.

But a crucial point is that there are likely to be winners and losers, just as there are with climate change. For example, a 2016 modeling study showed a 20 percent decrease in yields of ground nuts in India with SRM. There are also hints that geoengineering might shift some disease patterns around the world. And another paper has found that SRM would cause around 26,000 excess deaths each year starting in 2040 through various changes to air quality and other effects — but unchecked global warming itself would likely cause far more mortality, though shifted in the geographic details. This sort of research raises the thorny ethical quandary of whether to proactively harm certain people in order to help potentially more numerous others.

Other approaches dispense with such drilled-down specifics and try to offer reasonable approximations for overall well-being. A 2020 study led by then-Georgia Tech and U.C. San Diego graduate student Anthony Harding used economic models coupled with temperature and precipitation modeling to examine the effects of solar geoengineering and various climate change scenarios through 2100. He and his colleagues found that overall, lowering the global temperature with SRM “mitigates the economic harms of warming-associated climate change,” raising the global gross domestic product. But, more strikingly, they found that while climate change itself will exacerbate income inequality between countries — the rich get richer, the poor get poorer — geoengineering would reduce that inequality dramatically.

“It basically makes the poor countries better off compared to the rich countries,” Keith said. (Harding, the lead author of the paper in question, is now a postdoctoral fellow in Keith’s group, though Keith was not a co-author on that bit of research; geoengineering remains a fairly cloistered corner of the scientific world.) Keith said the magnitude of the result suggests it is likely a reliable outcome: “I think the underlying direction is very robust.”

Using income inequality between countries as a proxy for suffering certainly takes some of the difficulty out of determining more detailed numbers for hunger, or flooding, or fire, but as Harding and his colleagues readily admit, the idealized SRM scenario they model is not likely how it would go in the real world. What if most of the world’s nations collectively give the go-ahead for a geoengineering program, but a few resist, and a war breaks out as a result? That messy but very human sort of left turn isn’t trivial to work into a forward-looking computer model, but it could very easily change the calculus on suffering.

A slippery slope?

Another long-standing feature of the geoengineering debate is the concept of moral hazard, where the act of deploying SRM — or even doing the modeling research, let alone physical experiments like Harvard’s postponed Scopex — could hinder the world’s efforts to cut greenhouse gas emissions. The general idea is that an artificial way to cool the planet would give bad actors such as oil companies and petrostates an angle to lobby for slowed mitigation efforts.

Though it is difficult to prove this sort of possibility would come to pass — and the world isn’t exactly charging full steam ahead to fix climate change even without this supposed extra negative incentive — for the purposes of the net-suffering discussion, the concept does need to be considered. After all, a single year of burning coal, oil and gas causes millions of premature deaths, so any slowed progress away from these energy sources is highly meaningful from a human suffering perspective. How does this factor in?

Another common argument against SRM centers on governance. “It’s completely ungovernable — there’s absolutely no way that we would be able, as a collective global society, to agree on how to implement a solar geoengineering program,” said Jennie Stephens, director of Northeastern University’s School of Public Policy and Urban Affairs. She was one of several dozen academics and policy experts who recently put forth a so-called International Non-Use Agreement on SRM, essentially proposing to ban not only deployment of solar geoengineering but even some research and public funding for that research. (It is worth noting that the technology required to implement SRM, specifically planes capable of hauling the aerosols up past the point where similar aircraft can generally fly, does not yet exist. Experts agree, however, that it would not take all that much time or money to move past that obstacle.)

Scientists involved with SRM pushed back against this initiative and essentially pointed out that the arguments surrounding governance ignore the details of human suffering. “We clearly botched worldwide Covid vaccine governance, and yet we wouldn’t have been better off without vaccines rollout at all,” said Cornell University researcher Daniele Visioni on Twitter. An imperfect way to improve the totality of human existence is better than abandoning the project entirely.

View from the Global South

Holly Jean Buck, a scientist at the University of Buffalo focused on social and policy issues related to climate change and geoengineering, said that a reframing of the solar geoengineering conversation around its humanitarian potential could have concrete effects on what research is done, by changing the questions scientists seek to answer. “It would potentially … center vulnerable people, their needs, their concerns, their questions,” she said. She told a story of how she and some colleagues spoke with people living in the far north of Finland about their questions and concerns on SRM; those concerns led to some modeling analysis of how deploying the technology could affect winter conditions and more that provided meaningful answers. “The vulnerable people are the ones who stand the most to lose and the most benefit from some of these interventions,” Buck said.

There is a push to broaden the circle of scientists studying solar geoengineering to include more participants from the Global South, where climate change’s effects will be most pronounced. For example, a project called the Decimals Fund has awarded almost $1 million to scientists in developing countries. They will study things like SRM’s effects on hydro-climatic extremes in Indonesia, agriculture in Jamaica and health in Bangladesh. If the people who did not cause but stand to be most affected by climate change, and potentially gain the most from SRM, took the lead, that would certainly change the ethical parameters of the equation.

“It’s hard to see places like the U.S. having a legitimate basis to object to a solar geoengineering program that’s led by the Global South,” Ricke said. “We don’t really have a leg to stand on.”

In the end, the world may elect to forego solar geoengineering because it cannot agree on the particulars or the research actually says Y (suffering with geoengineering) is greater than X (suffering without it). Or maybe the ethical thorniness of the SRM trolley problem proves too much for the U.N. or other international collectives to overcome. But ignoring any intervention’s potential to make life better for more people seems, from an ethical standpoint, impossibly misguided.

“At stake is a moral dilemma,” wrote Pablo Suarez and Maarten van Alst, of the Red Cross Red Crescent Climate Center, in a 2016 paper on the humanitarian angle to solar engineering. “In the current climate, everybody has no choice but to be immersed in an experiment of planetary proportions. With or without geoengineering, we are all lab rats in the greenhouse.”

Thanks to Lillian Barkley for copy editing this article.