Solar geoengineering might reduce the economic impacts of climate change, but abruptly halting it could trigger a rapid temperature rebound known as termination shock, potentially causing greater damage than unchecked warming. Researchers warn that this risk underscores the need for sustained international cooperation. Without emission cuts, global temperatures could rise 4.5°C by 2100, leading to $868 billion in damages.
A new study highlights the double-edged nature of solar radiation modification (SRM), a proposed method to combat climate change by injecting sulphur dioxide aerosols into the stratosphere to reflect sunlight and cool the planet. While SRM could limit warming to 2.8°C above pre-industrial levels if started in 2020, thereby halving projected economic losses from $868 billion to around $434 billion by 2100, the dangers emerge if the program ends prematurely.
Francisco Estrada of the National Autonomous University of Mexico and his team modeled scenarios showing that a sudden termination in 2030 would cause temperatures to rebound by 0.6°C over eight years. This rapid spike, termed termination shock, could exceed $1 trillion in damages by century's end, surpassing the costs of unabated warming. "It would be much worse if we have a termination shock than if we did nothing," Estrada stated.
The research emphasizes not just total warming but its speed, as fast changes leave little adaptation time and risk tipping points like ice sheet collapse. Gernot Wagner of Columbia University praised the approach: "Solar geoengineering is riskier than it looks at first glance."
Real-world efforts, such as Make Sunsets releasing over 200 sulphur dioxide balloons—including in Mexico, prompting a ban threat—and Stardust raising $75 million to lobby the US, illustrate growing interest. A New Scientist survey found two-thirds of scientists anticipate large-scale SRM this century. However, sustaining it requires at least 100 aircraft dispersing millions of tonnes of aerosols annually, uninterrupted by conflicts or disruptions.
The study concludes SRM benefits only with termination risks below a few tenths of a percent yearly or a gradual phase-out over 15 years. In low-emission futures, up to 10% risk might be tolerable. Estrada described a "governance paradox": effective global mitigation would obviate the need for SRM, yet SRM demands such cooperation. Chad Baum of Aarhus University noted that funding research, like from The Degrees Initiative, aids vulnerable nations without sliding toward deployment. Wagner urged more studies on trade-offs amid rising emissions.
