Cloud brightening could cut super El Niño warming in half
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- Jessica Wan at UC San Diego led a study modeling marine cloud brightening — spraying seawater droplets into low-lying stratocumulus clouds over the eastern Pacific to make them whiter and reflect more sunlight back to space
- The simulation applied the technique to historical super El Niño events of 1997-1998 and 2015-2016, finding that nine months of spraying would have cut Niño 3.4 region warming nearly in half — from 2°C+ to just over 1°C — and ended El Niño by January
- The researchers drew their inspiration from Australia's 2019-2020 "black summer" bushfires, where drifting smoke particles brightened Pacific clouds and intensified the "triple dip" La Niña that persisted through three consecutive winters starting in 2020
- A hypothetical cloud-brightening mission would require an estimated 2,400 ships and volumes of seawater spray beyond current nozzle technology, but could downgrade a super El Niño to a moderate one
- Mat Collins at the University of Exeter warned that real-world cloud feedback — where warming seas dissipate low-level clouds — could demand more aerosol injection than the model assumes, calling the experiments "at the limit of what can be done"
- Both simulations showed an unintended consequence: the subsequent La Niña phase began earlier and became stronger after El Niño subsided, a pattern historically linked to drought and famine in regions like the Horn of Africa
- Wan argued short-term, targeted geoengineering like this sidesteps the "termination shock" risk of long-term approaches, since stopping the spraying would not unleash years of pent-up global warming
Why it matters: Super El Niños cost the global economy trillions in lost growth, and a super El Niño is currently developing in the eastern Pacific. This study opens a new frontier: geoengineering aimed not at long-term cooling but at disrupting specific climate cycles — yet the simulated side effect of a stronger follow-on La Niña means drought-vulnerable regions like the Horn of Africa could pay the price. The 2,400-ship scale and nonexistent nozzle technology put real-world deployment decades out.
