A termination shock could further increase the cost of climate damage

Solar geoengineering could be even more costly than unabated global warming if it were suddenly interrupted, leading to a “termination shock” of rapidly rising temperatures.

As greenhouse gas emission rates continue to rise, there is growing interest in solar radiation modification (SRM) to cool the planet, for example by spreading sulfur dioxide aerosols in the stratosphere to block solar radiation.

But solar geoengineering would have to continue uninterrupted for centuries or the warming that was “masked” would return at a faster rate. This rebound, known as a termination shock, would give humans and animals little time to adjust to the heat and could trigger climate tipping points such as ice sheet collapse.

Based on the established relationships between temperature rise and GDP loss, Francisco Estrada at the National Autonomous University of Mexico and his colleagues modeled the risks of climate inaction compared to the risks of solar geoengineering.

If humanity fails to reduce fossil fuel emissions, temperatures could reach a median of 4.5°C above pre-industrial levels by 2100, causing $868 billion in economic damage, researchers estimate. A hypothetical stratospheric aerosol injection program beginning in 2020 that kept the temperature rise to around 2.8°C could halve this damage.

But if the aerosol program were abruptly ended in 2030 and temperatures rebounded by 0.6°C over the next eight years, the damage could exceed $1 trillion by the end of the century. While the numbers may be higher or lower in real life, “the message doesn’t really change,” Estrada says. “It would be much worse if we get a termination shock than if we do nothing if we have unabated climate change.”

The study is innovative in estimating damage based not only on overall warming, but also on how fast it’s coming, he says Gernot Wagner at Columbia University in New York.

Solar geoengineering “is riskier than it first appears,” he says. “That’s the post.

Silicon Valley start-up Make Sunsets already did released more than 200 sulfur dioxide balloons into the stratosphere to sell emissions offsets. This included a launch in Mexico that prompted the government to threaten to ban geoengineering.

The Israeli company Stardust has raised 75 million dollars and lobbied the US government on solar geoengineering. According to a survey conducted by the company, two-thirds of scientists expect large-scale SRM this century The new scientist last year.

It would take at least 100 airplanes to cool the Earth by 1°C spreading many millions of tons of sulfur dioxide into the stratosphere each year without interruption by political strife, wars, pandemics, or other black swan events.

Today, major players such as the US are actively undermining international cooperation on climate policy, but this kind of cooperation would be necessary to avoid termination shock and make SRM a net benefit, the researchers conclude.

From a graph of different combinations of parameters, they found that aerosol injection is likely to reduce climate damage only if the probability of its termination in any given year is only a few tenths of a percent, or if that termination could be limited over more than 15 years.

If the country reduces emissions and only a small amount of geoengineering cooling is needed, aerosol injection can be beneficial with a termination probability of up to about 10 percent. Although a 10 percent probability of termination in any given year implies a 99.9 percent probability of failure over the century, the temperature rebound should be small in this low-emissions scenario.

This need for international climate cooperation reveals what Estrada calls the “governance paradox” of solar geoengineering. “The probability of failure has to be very, very low; you have to be able to handle if things go wrong and, importantly, you have to have very good mitigation management,” he says. But “if you are able to… manage the problem of global greenhouse gas emissions reduction, then you wouldn’t really need SRM”.

These findings suggest that solar geoengineering research is not necessarily the “slippery slope” for its deployment that some have claimed. Chad Baum at Aarhus University in Denmark. Funding for the new work came from The Degrees Initiative, which funds geoengineering research in more vulnerable, low-income countries.

“You want to have all the steps of the research … to have more input from the affected communities,” says Baum, who also works with Degrees.

But as emissions and climate impacts increase, more research is still needed on the trade-offs of geoengineering, Wagner says. “We’re pushed to the wall,” he says.

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