As climate change worsens, the once-unimaginable power to use technology to cool the planet—a method known as “solar geoengineering”—has quietly entered the realm of possibility. Yet the prospect of developing such planet-altering technologies has launched an intense debate: Can this be achieved responsibly? Should it be attempted at all?

A report released by the National Academy of Sciences in March 2021—Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance—identified some governing principles for socially and environmentally responsible research into controversial climate-altering “geoengineering” technologies. But is pointing the way toward a responsible research agenda for such a powerful technology enough?

History shows us that such principles—even when powerfully articulated by scientists and international governing bodies—prove to be an insufficient constraint on the actors who actually decide how a powerful new technology will be used. Impersonal economic and geopolitical forces determine how such powerful technologies are developed and deployed to a far greater extent than any group of regulators.

If we hope to avoid a misuse of geoengineering, then, it is essential we rely upon more than researchers’ intentions to uphold principles. We must also focus on making tangible progress towards decarbonization and sustainable development. 

Ice, Clouds, and Sulfur

So what’s the science behind geoengineering technologies—and how might they mitigate the impacts of climate change? At present, they are theoretical systems that aim to create large-scale cooling in the Earth’s climate. Such technologies are divided into two categories: Solar Radiation Management, (SRM) and Carbon Dioxide Removal (CDR).

The goal of CDR is to directly remove carbon and other greenhouse gases from the atmosphere. It’s a relatively non-controversial and essential technology, but it also will require decades of cost-intensive work to be deployed.

Research into Solar Radiation Management (SRM), however, is more controversial—and likely will  scale up for potential use more quickly. It envisions ways that technology might increase the Earth’s  “albedo effect”—or the rate at which solar radiation is reflected away from the earth. The higher the albedo effect, the less solar radiation is absorbed by the earth.

This effect occurs naturally through reflective surfaces such as icebergs and clouds, but the development of SRM technologies attempts to artificially replicate and amplify these natural processes, including Stratospheric Aerosol Injection (SAI), Marine Cloud Brightening, and Stratospheric Aerosol Injection. 

All of these methods would reflect sunlight away from the Earth at a greater rate, producing an artificial cooling effect on the planet. But Stratospheric Aerosol Injection is both the most powerful and controversial tactic, because it involves the use of planes to disperse reflective particles into the atmosphere over an extended period.

While the large-scale reflection of sunlight occurs naturally in the form of massive volcanic eruptions that dispersed large quantities of sulfur into the atmosphere SAI is an attempt to replicate such eruptions artificially. 

Solar radiation management technologies have yet to be developed or tested to a significant degree. But the scientific consensus is that they are feasible. One perceived factor in its favor is cost: SRM is anticipated to be less expensive than any other mitigation strategy. Another factor is speed. Depending on size and duration of the deployment, the desired cooling effect would take hold in a matter of months.

Navigating a “Slippery Slope”

Yet “hacking” the planet in the way envisioned by SAI—and other solar radiation management strategies—raises serious concerns. Critics caution that the ecological side effects of solar geoengineering could be dire, and theoretical research suggests a solar-geoengineered world could generate a range of new stressors to environmental security.

How so? While SRM would cool the planet, it would not address the root driver of climate change (greenhouse gas emissions) and do nothing to alleviate other ecological impacts of climate change, such as ocean acidification and soil degradation. The scale on which SRM would need to be deployed also would likely create unintended impacts on agriculture, human health, and already fragile ecosystems.

The lack of a safe and effective “off” switch is also a major concern. If the deployment of SAI or other  technologies were to suddenly cease after a long period of use, the planetary system would experience the cumulative warming effect of the greenhouse gases accumulated in the atmosphere since the beginning of the cooling period. This “termination shock” could result in mass extinctions and ecological collapse, as rapid warming kills plants and insects at the bottom of the food chain faster than larger animals could find new food sources. In short, it would present a threat to the foundations of life on the planet.

Solar radiation management also raises serious (and broader) environmental justice concerns.  As a global climate-altering technology, it will directly impact the countries of the global south and indigenous peoples who are already the most vulnerable populations to climate change. The deployment of geoengineering by powerful states (including the United States) also could perpetuate existing climate injustices, creating additional barriers to a more resilient and sustainable planet.

Given its disruptive potential, critics warn that even research into SAI and other similar technology be undertaken with caution. It might even create a “moral hazard” in which its  existence as a perceived “plan B” reduces the necessary urgency to advance decarbonization and other sustainable development efforts. Investors in the new technology will expect a concrete return on their investment, thereby creating a “slippery slope” to deployment. 

Owning the Outcomes

The authors of Reflecting Sunlight identify key principles that should govern geoengineering research. They emphasize a  multidisciplinary approach, including racial and economic diversity, collaborative sharing of research between nations, and perspectives from developing countries and the global south.

Yet the National Academy of Sciences report also lays down even broader markers. Its authors see geoengineering as serving a limited role in a larger adaptation strategy meant to ease the transition a carbon-free world economy, and not as an acceptable substitute. The report identifies the need for “exit ramps” to terminate research that does not align with these principles.

Yet even as the authors of Reflecting Sunlight seek to minimize the likelihood of misusing geoengineering, their efforts inevitably run up against the unprecedented power of these promised technologies. International agreements can propose essential regulations, but their ability to serve as reliable constraints on geoengineering depends ultimately on domestic political conditions. Economic and geopolitical concerns could easily trump not only a responsible research agenda, but also its development and deployment of solar engineering technologies in a warming world.

History offers an unhappy preview of how restraint by researchers likely cannot counter strong incentives for misuse or weaponization of powerful technologies.  First, the decisions taken regarding the development and use of geoengineering will not be made by current theorists, but by future leaders facing the ecological, economic, and national security consequences of our lack of progress in reducing fossil fuel emissions. The future of what results from research will not reside entirely in present measures taken to guide it.

Yet other factors also make regulation of this technology difficult. Powerful emerging technologies such as SRM cause social, economic, and technological systems to transform and adapt around them. In our modern interconnected world, these transformations can be highly difficult to reverse once they have taken hold. “The essence of controlling a technology is not in forecasting its social consequences,” writes David Collingridge in his 1982 book, The Social Control of Technology, “but in retaining the ability to change a technology, even when it is fully developed and diffused.”

When an emerging technology exhibits an early competitive advantage over alternatives, it can trigger a series of feedback loops. The eventual outcome is a “socio-technical lock-in,” in which social, economic, and technological systems become mutually dependent to the point where they are difficult to separate—even if they become harmful or a superior alternative emerges.

Decarbonize Now To Prevent Lock-In

Major efforts to decarbonize the global economy have not yet taken root. It takes time to lay foundations for adaptation strategies that will be sustainable in the long run. The complex time and effort-intensive nature required to do so make it a preemptive, rather than a reactive strategy.

Yet Solar Radiation Management possesses qualities that make it likely to be used in reaction to runaway climate change. It works quickly. It is (relatively) cheap. Current estimates of a hypothetical 15-year deployment ramp for SRM in the United States run at about $15 billion, making it far less expensive (in the short term) than either emission abatement or the economic costs of a warming climate. And this technology promises to be relatively easy to deploy on short notice, possibly as a reaction to the harsh consequences offered by our failure to decarbonize. In short, SRM likely offers a short-term comparative advantage over more responsible and sustainable alternatives.

The path to global powers continuing to invest in SRM at the expense of the more complicated and cost-intensive ways to  decarbonize and develop sustainably is clear. But we also see the dangers of substituting SRM technology, despite its short-term comparative advantages.  The resulting path-dependency and socio-technical lock-in would make large-scale decarbonization even more difficult, thereby exposing future generations to the risks of life in a geoengineered world.

Because SRM technologies have yet to be developed on a large scale, it is tempting to see the role they will play in the future of our species and our planet as questions for tomorrow, and not today. Such thinking is a mistake.

Now is the time to push forward more aggressively with decarbonization programs. This is especially as the current lack of progress around decarbonization suggests that SRM technologies will be advanced as part of an overall adaptation strategy.

The dynamics of path dependency and sociotechnical lock-in suggest that will have far less control over their use if they are deployed as a desperate reaction to cascading climate impacts. We can only hope that if—or, more likely, when—solar radiation management measures are is deployed, large-scale decarbonization of our energy system will be already well underway.