In a Warmer World, Cloud Brightening Could Backfire, Study Finds

To keep warming in check, some experts have proposed brightening clouds over the ocean to reflect more of the sun’s light. A new study finds that doing this in the north Pacific could, in the future, actually worsen heat in Europe.

The churn of ocean water sends sea salt spraying into the air, naturally brightening big, puffy ocean clouds. As water condenses around airborne salt particles, it reflects light from the sun. Some scientists have called for amplifying this process to reflect more light and slow warming. In California, researchers have sprayed small amounts of sea salt into the air over San Francisco Bay to study the effect.

Farther south, at the University of California, San Diego, researchers recently modeled the impact of cloud brightening if deployed on a massive scale, with ships scattering salt into the air across huge swaths of the north Pacific every spring, summer, and fall for 30 years.

They found that brightening would cut the risk of dangerous summer heat in North America. Though, their modeling showed it would also curtail rainfall in both Alaska and the Sahel region of Africa.

Looking ahead, researchers examined the effect of brightening in 2050, in a world that had warmed by 2 degrees C. In that scenario, brightening would no longer curb the regional risk of summer heat. It would, however, intensify heat over most of Europe. The findings were published in Nature Climate Change.

UCSD climate scientist Katharine Ricke, coauthor of the new paper, has previously argued for investigating the impact of reflecting sunlight to cool the planet. Writing in Nature, she said that while cloud brightening can help protect against warming, “we have very little evidence on how this would affect weather, agriculture, human health, or other living things.”


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