schirinrangnick

A technique known as stratospheric aerosol injection could potentially help the world limit climate change, according to a new study by Yale and Harvard researchers.

Published on Nov. 23 in the journal Environmental Research Letters, the study explains that this method, which has not yet been perfected, would generate the same effects as a volcano, which, after a major eruption, sends sulfate particles into the stratosphere. These particles increase the amount of reflected sunlight that leaves the atmosphere of the Earth, and with less sunlight reaching the planet, the effects of global warming are decreased.

“It increases the reflectivity of the Earth such that a little bit less of the sunlight that comes to the Earth, penetrates and stays in the Earth. … There’s only a proportion of the sunlight that hits the Earth that goes into the climate system,” said Yale researcher Wake Smith ’79, co-author of the study. “This is what happens naturally when a big volcanic eruption occurs.”

This technique is undoubtedly effective at mitigating the effects of climate change, according to Smith and UCLA researcher Jesse Reynolds, who both cited evidence from volcanic eruptions. Unfortunately, they agreed that the method is not a solution to climate change. To truly combat climate change, the world will need to reduce and even eliminate carbon emissions, which this method does not attempt to do, they said.

Instead, stratospheric aerosol injection would be a way to buy time as the global community works to reduce carbon emissions. The technique would decrease the rate that the planet warms as researchers search for better and more permanent solutions to climate change.

“It doesn’t solve climate change. And engineered climate, engineered in this way, won’t be the same as the pre-industrial climate or the climate today, for that matter. It will be warmer in some places and cooler in some places, it may affect precipitation cycles,” Smith said. “While it could reduce the average surface temperature of the planet, it doesn’t mean it will return the climate in every place to the way the climate was.”

Smith and Reynolds both said that there are many potential issues with this technique, including whether implementation is even possible. According to Reynolds, the basic technologies for implementation exist but need significant refining to enable them to function with the precision necessary to ensure the technique’s success.

Moreover, it is also unclear exactly what country or transnational organization would ratify this strategy. There is currently no definite transnational body responsible for approving such a strategy or overseeing its maintenance.

Additionally, as Smith indicated, many of the side effects are unknown and would need to be studied more comprehensively before the injections could begin. For these reasons, both scientists agreed that aerosol injection will hopefully never have to be used, but rather can serve as one of a few backup plans — including others also under the umbrella of solar geoengineering — if humans are unable to reduce emissions quickly enough.

Many believe solar geoengineering methods such as this one should not be considered due to potential unforeseen side effects, including extreme weather events. Reynolds said, however, that he believed all options should be on the table.

“My perspective is that climate change is a serious enough risk that we need to take all options seriously. Solar geoengineering needs to be assessed thoroughly and rationally and should be discussed in appropriate political and governance forums.” he said. “I hope this never needs to be used.”

Nevertheless, there are a large number of scientists working on the issue, Reynolds said. He estimated that there are a couple hundred scientists studying this topic and about 700 published papers on solar geoengineering, most of which focus on the aerosol injection technique.

Despite the breadth of research on the topic, a fully functioning aerosol injection method is still a number of years away. While the paper discussed the possibility of beginning to inject aerosol into the stratosphere in 15 years, both Smith and Reynolds clarified that this was an optimistic estimate.

“I think there are good reasons to proceed with caution.” Reynolds said. “I think research should ramp up and out, but I think it’s going to take many years before uncertainties are reduced enough so we might be able to proceed with some degree of confidence.”

Even if the world is unable to eliminate emissions, aerosol injection still may not be the best way to reduce the warming of the planet relatively quickly, according to Smith. Even if we eliminated all emissions today, the planet would still warm an additional 1.5 degrees Celsius, Reynolds explained. And even if emissions are eliminated in about 15 years, Earth’s temperature would still rise by two degrees, which the Paris climate agreement marked as the maximum warming for the planet to remain safe.

Smith emphasized that while the main priority is eliminating carbon emissions, there needs to be multiple backup plans, especially given the magnitude of emission reduction required to keep the Earth inhabitable. Still, aerosol injection is just one of those plans.

“We should perceive this as an emergency remedy, not as the solution to climate change. We hope to not to have to use it,” he said. “There are other climate interventions that would be better than this one.”

In June 2017, President Donald Trump announced that the United States would withdraw from the Paris agreement.

Emmett Shell | emmett.shell@yale.edu