Targeted marine cloud brightening could neutralize super El Niño events, model study finds
A new modeling study finds that deliberately brightening marine clouds over the Pacific could significantly weaken or even neutralize a developing El Niño, potentially sparing the world from its most destructive impacts.
A climate pressure point
The El Niño-Southern Oscillation (ENSO) is one of the most powerful natural climate cycles on Earth. During an El Niño event, weakened trade winds push warm water toward the coast of South America, heating the tropical Pacific and distorting global weather patterns. This year's El Niño is on track to be among the strongest on record, with forecasts warning of extreme heat, droughts, floods and cyclones. Combined with the background warming from fossil fuel burning, its economic toll could reach hundreds of billions of dollars.
El Niño is one of these things where something happens in the tropical Pacific, and then it rearranges the way the entire global atmosphere is holding energy that year. It's an ultimate pressure point in the climate system.
How cloud brightening works
Marine cloud brightening (MCB) is a geoengineering technique first proposed by British cloud physicist John Latham in 1990. The idea is to spray fine sea salt particles into marine clouds, making them brighter and more reflective, so they bounce more sunlight back into space. Unlike other solar geoengineering methods that operate globally, MCB can be applied regionally. The new study, published in Science Advances on 8 July, explores whether targeting a vast rectangular zone in the equatorial Pacific could cool the sea surface enough to stifle an emerging El Niño.
We were able to turn what was an extreme or super El Niño into a neutral event, so it wasn't even an El Niño anymore at that point.
Lessons from Australian megafires
The researchers were inspired by a recent natural experiment: the catastrophic bushfire season in Australia in 2019 and 2020. Those fires injected nearly 1 million metric tons of smoke into the atmosphere, one of the largest such inputs observed by satellites. The smoke aerosols interacted with low clouds over the southeastern subtropical Pacific, making them brighter and reducing the amount of heat reaching the surface. This phenomenon is now believed to have contributed to the unusually long La Niña that lasted from 2020 to 2023.
It was the key breakthrough for this to become a viable research question. Without that validation opportunity, I don't think our findings would be so credible.
Modeling a geoengineered future
To test the concept, Wan and Ricke used a well-established climate model to simulate what would have happened if MCB had been deployed during the major El Niño events of 1997–1998 and 2015–2016. They found that the intervention worked best when started early, in June, and sustained through February. The simulations showed that cloud brightening could have significantly weakened both events, potentially preventing some of the worst impacts on land.
But the reason people would ever care about this is not temperature in a box in the Pacific, but how the impacts translate over land.
- Study models MCB intervention that would have weakened the event
- Study also models intervention for this super El Niño
- Australian bushfires inject smoke that brightens clouds, contributing to subsequent La Niña
- Triple-dip La Niña occurs, partly attributed to brightened clouds from wildfire smoke
- Super El Niño forecast; study proposing MCB is published on 8 July
Cautions and unknowns
The authors stress that their work is a first step and that real-world deployment would carry risks and uncertainties. Geoengineering remains deeply controversial, and unintended consequences could ripple through the climate system. The study was supported by the U.S. National Science Foundation, NASA, the Department of Energy and NOAA. The researchers hope their findings will prompt governments to consider a wider portfolio of responses to climate change.
