The escalating pace of greenhouse gas emissions has spurred a renewed focus on solar radiation modification (SRM) techniques, such as disseminating sulfur dioxide aerosols into the stratosphere to deflect sunlight and cool the planet. However, this approach carries a significant, often overlooked, cost.
Implementing solar geoengineering would necessitate continuous, centuries-long deployment. A sudden cessation would unleash a “termination shock,” causing a rapid resurgence of previously masked warming. This abrupt temperature rebound would leave both human populations and ecosystems with minimal time to adapt, potentially triggering critical climate tipping points, including the collapse of ice sheets.
Modeling the Economic Fallout
Francisco Estrada, affiliated with the National Autonomous University of Mexico, and his colleagues undertook a modeling study to compare the economic risks associated with climate inaction against those posed by solar geoengineering. Their research, which established links between temperature increases and Gross Domestic Product (GDP) loss, provides critical insights.
Their projections indicate that if global efforts to curb fossil fuel emissions falter, average temperatures could rise by a median of 4.5°C above pre-industrial levels by the year 2100. Such a scenario is estimated to result in economic damages amounting to $868 billion. In contrast, a hypothetical stratospheric aerosol injection program initiated in 2020, which successfully limited temperature increases to approximately 2.8°C, could potentially halve these projected damages.
The Devastating Impact of Interruption
The study highlights a stark risk: if this hypothetical aerosol program were to be abruptly terminated in 2030, leading to a 0.6°C temperature rebound within the subsequent eight years, the total economic damages by century’s end could exceed $1 trillion. While real-world figures may vary, Estrada emphasizes that the core message remains unchanged: the consequences of a termination shock would be far more severe than experiencing unabated climate change.
Gernot Wagner, based at Columbia University in New York, notes the study’s innovative approach in quantifying damages based not solely on the extent of warming, but also on its rate. He suggests that solar geoengineering “is riskier than it looks at first glance,” a crucial contribution of this research.
Commercial Ventures and Scientific Expectations
Commercial interests are already engaging in SRM activities. Make Sunsets, a Silicon Valley start-up, has deployed over 200 balloons releasing sulfur dioxide into the stratosphere, offering these actions as emission offsets. A launch in Mexico by the company even led the Mexican government to consider a ban on geoengineering.
Meanwhile, the Israeli company Stardust has secured $75 million in funding and actively lobbied the U.S. government regarding solar geoengineering. A survey conducted by New Scientist last year revealed that two-thirds of scientists anticipate large-scale SRM deployment within this century.
The Uninterrupted Necessity and Governance Challenges
To achieve a 1°C global cooling, an estimated 100 aircraft would need to continuously disperse millions of tons of sulfur dioxide into the stratosphere annually. This operation must remain uninterrupted by political disputes, conflicts, pandemics, or other unforeseen catastrophic events.
The researchers conclude that international cooperation, which is currently being undermined by major actors like the U.S. on climate policy, would be essential to avert termination shock and ensure SRM offers a net benefit. Their analysis, based on various parameter combinations, suggests that aerosol injection is likely to mitigate climate damages only if the probability of its termination in any given year is extremely low, on the order of a few tenths of a percent. Alternatively, a gradual tapering off over more than 15 years could also prove beneficial.
Conditional Benefits and the Governance Paradox
Under scenarios where countries significantly reduce emissions, and only a minor degree of geoengineered cooling is required, aerosol injection might be viable even with termination probabilities as high as 10 percent. Although a 10 percent annual termination risk translates to a near-certainty of failure over a century, the resulting temperature rebound would be less severe in a low-emissions context.
This dependency on global climate cooperation illuminates what Estrada terms the “governance paradox” of solar geoengineering. He explains that the probability of failure must be exceedingly low, requiring robust management capabilities for unforeseen issues and, crucially, strong governance structures for mitigation. However, if societies possess the capacity to effectively manage the global mitigation of greenhouse gases, the necessity for SRM would diminish.
Research Directions and Community Involvement
Chad Baum of Aarhus University in Denmark suggests that research into solar geoengineering does not inherently represent a “slippery slope” towards its deployment, countering arguments from some quarters. The research that generated these findings received funding from The Degrees Initiative, an organization supporting geoengineering research in vulnerable, low-income nations.
Baum, who also collaborates with Degrees, emphasizes the importance of incorporating input from affected communities at all stages of research. He states, “You want to have all steps of the research… have more input from the communities affected.”
Given the ongoing rise in emissions and their climate impacts, Wagner asserts that further research into the trade-offs of geoengineering remains vital. He observes, “We are forced against the wall.”
Journal reference: Environmental Research Climate DOI: 10.1088/2752-5295/ae33df