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Dimming the sun could cause chaos, scientists warn

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October 22, 2025
4 min read

Dimming the sun could cause chaos, scientists warn

One of the more radical approaches to combat climate change is dimming the sun, an idea once thought of as science fiction. It would involve cooling the Earth by scattering sunlight-reflecting particles in the upper atmosphere, a technique known as stratospheric aerosol injection (SAI). The radical idea is now being seriously considered by researchers.

The aim of dimming the sun is to offset global warming by mimicking the cooling effects of a volcanic eruption, with hundreds of scientific models exploring how it could work. But researchers from Columbia University advise caution, saying that these models are overlooking how complex, uncertain, and potentially risky dimming the sun could be.

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“Even when simulations of SAI in climate models are sophisticated, they’re necessarily going to be idealized,” atmospheric chemist and aerosol scientist at Columbia’s Climate School and Columbia Engineering, V. Faye McNeill said. “Researchers model the perfect particles that are the perfect size. And in the simulation, they put exactly how much of them they want, where they want them. But when you start to consider where we actually are, compared to that idealized situation, it reveals a lot of the uncertainty in those predictions. There are a range of things that might happen if you try to do this, and we’re arguing that the range of possible outcomes is a lot wider than anybody has appreciated until now.”

In a study published in Scientific Reports, McNeill and her team explored the physical, as well as economic and political barriers that make SAI more complex. They reviewed existing research to better understand how its results would depend on details such as how and where SAI is deployed, with key factors including the altitude and latitude of particle release, the time of year, and the quantity of materials in the atmosphere.

Among them, latitude has the greatest impact, they found. SAI concentrated by the poles could disrupt monsoons, while near the equator could impact jet streams and interfere with global air circulation.

“It isn’t just a matter of getting five teragrams of sulfur into the atmosphere. It matters where and when you do it,” says McNeill. These mean that, if SAI is actually going to be explored, it needs to be done in a centralised and coordinated manner, something that researchers say is unlikely due to geopolitics.

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