The Case for Researching Solar Geoengineering

Editor’s Note: This is the first in a two-part series on the case for researching the taboo concept of solar geoengineering as a potential bridge to achieving net zero emissions. This piece summarizes some concerns raised about solar engineering. Part two analyzes the use of stratospheric aerosol injection and what we need to research further if we want to know how to effectively deploy and regulate it.

This year, much like 2021 before it, has been a record-shattering year of compounding climate disasters: an unprecedented heat wave in South Asia; the second-most-damaging hurricane in the history of the United States; flooding in Pakistan that has displaced 33 million people, damaged the country’s wheat crop, and will likely trigger a famine; and historic droughts in China, the western U.S., and Europe that have reduced power generation and river commerce, rocked insurance markets, and spiked food prices. Scarier still, it’s nearly certain that 2023 will set new climate records, as will 2024, 2025, and on and on for the foreseeable future. 

Humanity is staring down the barrel of a crisis-laden future; what’s already happened is a relatively benign preview of what’s to come. Yet growing recognition of climate change has not translated into meaningful progress, at least from the perspective of the atmosphere. Climate change is driven by the total stock of greenhouse gas (GHG) pollution in the atmosphere, meaning society needs to zero out emissions—not merely reduce the emissions rate—to stop climate change from getting worse. Yet GHG emissions are accelerating: Between 2020 and 2022, atmospheric GHG concentrations grew at faster rates than in years prior. 

To have any chance of safely stabilizing the climate, the policy consensus—derived from sophisticated modeling—calls for transformational change. Not only does society need to reconfigure global energy infrastructure and land use on an unprecedented scale, at a likely cost well into the trillions of dollars, but it also needs to rely—heavily—on carbon dioxide removal technologies that were, just within the past few years, a twinkle in the eyes of the scientists and engineers developing them. In the best-case scenario, this transformation will occur over the next few decades while people adapt to worsening climate impacts. And, hopefully, the transformation will happen before the climate reaches an irreversible (on human timescales) tipping point (assuming, of course, that hasn’t happened already).

Hence the increasingly loud murmurs, in certain circles, about solar geoengineering. In a nutshell, solar geoengineering is the intentional modification of Earth’s atmosphere to reflect more sunlight back into space, with the goal of cooling temperatures on a regional or planetary scale. The most discussed and best understood of these techniques is stratospheric aerosol injection—the idea, basically, of using aircraft to release a thin “veil” of aerosols high up in the atmosphere to reflect away a small amount of sunlight. 

Everyone agrees that dramatically reducing GHG emissions is essential to addressing climate change, but some see solar geoengineering as a sort of “bridge” to a zero-emissions world or, to use a different metaphor, an insurance policy in case the world cannot decarbonize quickly enough to avoid catastrophic climate impacts. For those who see climate change as a likely planetary emergency, geoengineering may provide a regrettable but necessary way to buy time to improve and commercialize decarbonization technologies, invest in new infrastructure, and, perhaps, prevent runaway warming.  

To be sure, not everyone accepts this view of geoengineering. Although there have been recent research initiatives by the National Academies for Sciences and the White House Office of Science and Technology Policy, geoengineering remains largely taboo within climate policy circles. Indeed, “controversial” is too weak a word to describe the vehement opposition that geoengineering generates. When it is mentioned at all in official communiques, it is by oblique reference and ellipsis. For instance: The Paris Agreement—like the United Nations Framework Convention on Climate Change before it—makes no express mention of geoengineering; the U.N. Environmental Assembly shot down a proposal to explore solar geoengineering in 2019; and the Intergovernmental Panel on Climate Change (which compiles regular and authoritative reports on climate science) has given the subject only cursory treatment. More recently, a group of researchers has conveyed their “alarm” that geoengineering has become an increasingly legitimate topic of scientific inquiry. They advocate for a broad international prohibition on solar geoengineering research.

The reticence around geoengineering arises from legitimate concerns. The first is the persistence of a fractious and, frankly, somewhat bitter divide in international climate policy between historically large emitters (the developed world plus China and, increasingly, India) and the developing world (India belongs in this camp, too). There is a widely shared fear that, if geoengineering is on the table, policymakers will not only use it but also abandon (or devote relatively fewer resources to) reducing greenhouse gas emissions and funding adaptation measures. In particular, some observers are worried that those countries most historically responsible for emitting greenhouse gasses will use geoengineering as cover to shirk their duty to mitigate their fair share of GHG emissions. The concern is borne out of past and present experience, as developed countries and large emitters have often recognized their mitigation obligations only in the breach.  

There is also a related but distinct argument that there is no practicable way to develop a legitimate decision-making structure that could authorize a geoengineering deployment program. Any decision-making body would inevitably be dominated by powerful countries whose material interests may diverge—widely—from those of developing countries.  

The second concern is more of a gut reaction. It is, broadly speaking, a rejection of the human hubris inherent in literally engineering the atmosphere. This objection is also informed by a skepticism about the limits of human knowledge, especially given the complexity of the atmosphere, global climate, and the human systems influenced by it.

These are justifiable concerns, and reasonable minds could disagree about how to weigh the relative risks. But a hotter world could become a more desperate world, and countries may reach for solar geoengineering no matter how little it has been studied or how few governing institutions are in place. Even were a research ban desirable, the world is unlikely to keep solar geoengineering at bay indefinitely. The incentives for research are already strong and will only grow stronger in the medium term.

Funding more scientific research may reduce the enormous uncertainties around solar geoengineering’s possibilities and limitations, and clarify whether it is a tool to avoid suffering and harm, a dead end, or something more ambiguous—that is, a powerful but imprecise tool that has adverse effects and troubling distributional consequences. Now is the time to set the groundwork for meaningful, if difficult, conversations about solar geoengineering as one component of a robust climate policy.   

Those conversations will be difficult, because—as we will highlight in our next article—although solar geoengineering may be appealing in theory, the science is undeveloped, and it remains possible that its potential is more limited—or its usage more fraught—than many assume.