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Engineers could combat climate change by tinkering with Earth’s atmosphere, but it’s a risky option.


A solar shield could save us from climate change. But its sudden collapse would doom the planet

Last year, the planet was plagued by powerful hurricanes, blistering fires, and temperatures that ranked as some of the hottest on record—ratcheting up concern that we’re already knee-deep in climate change. To stave off the heat, some scientists have proposed blanketing Earth in a sheet of sunlight-reflecting particles called aerosols. This solar shield could cool the planet and buy us time, but a new study suggests that if politicians turned off the hypothetical cloud, they could plunge the planet into a sudden ecological Armageddon.

The idea of injecting aerosols into the atmosphere first came to prominence in 2006, when Nobel Prize–winning atmospheric chemist Paul Crutzen argued that scientists should actively explore the possibility. He said it would be similar to what happens naturally following some volcanic eruptions. For example, the 1991 Mount Pinatubo eruption in the Philippines cooled the planet by 0.5°C, after spewing some 20 million tons of sulfur dioxide into the stratosphere. The gas created a sulfate aerosol cloud that reflected sunlight back to space for 2 years.

But injecting aerosols would require constant maintenance—and continuous global support. If a severe drought, a new government, or an economic downturn triggered its sudden collapse, the planet would rapidly warm to the steamy temperatures we otherwise would have been facing. “The minute you stop it you get the full force of the total emissions you’ve put out and that are still in the atmosphere,” says Camille Parmesan, a climate change biologist at the University of Plymouth in the United Kingdom and the University of Texas in Austin who was not involved in the new study.

Now, scientists have asked another question: How would such a collapse impact the world’s biodiversity? Christopher Trisos, an ecologist at the University of Maryland in Annapolis, and colleagues set out to answer that question by figuring out how fast plants and animals would have to move to escape changes in their local climate, with and without a stratospheric cloud. In their simulation, starting in 2020, planes would inject 5 million tons of sulfur dioxide into the stratosphere, essentially mimicking an eruption a quarter the size of Mount Pinatubo. That would continue year after year until 2070, at which point a geopolitical disaster—or some other event—would cause maintenance to cease. All the while, humans would continue emitting carbon into the atmosphere at rates that would peak midcentury and then begin to reduce.

Trisos’s team found that the aerosols initially lowered global temperatures by a quarter of a degree Celsius. But even with the cloud, the planet gradually warmed from 2030 to 2070. The big spike came when the aerosol injection failed—in the model, global temperatures shot up by nearly three-quarters of a degree in just 10 years. The researchers calculated that in order to keep up with this rapid temperature change, land-based species would need to permanently move their range by 10 kilometers per year. That’s four times faster than the speed at which they have to flee current climate change. But the story’s even worse for marine species—they’d need to move six times faster to escape the effects of rapid climate change, the team reports today in Nature Ecology and Evolution.

Species would have to move particularly quickly in tropical oceans and the Amazon—places that house a lot of the world’s biodiversity. This would put corals, frogs, and other slow-moving tropical species at risk of extinction. To make matters worse, many species are already lagging behind in their climate migrations. “Gradual climate change, which is happening now, is bad enough, but if we do something that makes climate change much faster, then it could be devastating for certain species,” says Alan Robock, a climate scientist at Rutgers University in New Brunswick, New Jersey, and a co-author of the study.

If the world took up a stratospheric aerosol project, the only way to avoid disaster, wrote Gavin Schmidt, a climate scientist at the NASA Goddard Institute for Space Studies in New York City, would be to have a permanent global commitment. “This will never be a sustainable option because such a system is inherently fragile.”

Parmesan agrees: “It’s very clear from what has happened with our latest presidential election that we cannot trust [international] agreements.”