UC San Diego climate scientists are floating a bold idea for taking the edge off a looming “very strong” El Niño: make certain Pacific clouds a bit brighter so the ocean below does not heat up quite as much.
Researchers at UC San Diego’s Scripps Institution of Oceanography say that deliberately brightening low clouds over parts of the southeast Pacific could blunt the peak impacts of powerful El Niño events, based on new seasonal forecasting experiments. Using smoke from the 2019–20 Australian “Black Summer” bushfires as a kind of natural dress rehearsal, the team ran model scenarios and found that targeted cloud brightening can markedly reduce the ocean heating and the downstream extremes that make El Niño so damaging. The work appears this week in the journal Science Advances.
How the team put the idea to the test
The authors replayed two of the strongest El Niño events on record, 1997–98 and 2015–16, while switching on modeled marine cloud brightening over the southeast subtropical Pacific, according to Scripps Institution of Oceanography. They used the vast 2019–20 Australian “Black Summer” smoke plume as a validation case, checking that the model reproduced the same cloud-brightening fingerprint before experimenting with any deliberate interventions.
In many of the experiments, early and sustained cloud brightening reduced El Niño’s ocean warming and weakened its global rainfall and temperature teleconnections. In plain language, the models suggest that tweaking clouds over one patch of ocean could dial down extreme weather patterns that typically ripple around the world during a supercharged El Niño.
What a seasonal ‘sunscreen’ would involve
The researchers argue that a seasonal or event-specific deployment could, in principle, blunt extreme El Niños if it started soon after the spring predictability barrier and stayed in place through the peak of the event. They also stress that the window for effectiveness is narrow and that timing and duration matter a great deal. This would not be a set-it-and-forget-it global thermostat, more like a finely timed, regional “sunscreen” for the ocean surface.
No immediate tests and major caveats
The study’s authors say they are not aware of any concrete plans to test marine cloud brightening on the El Niño that is now forming, and they emphasize that more modeling and impact assessments are needed before any real-world experiment, according to EurekAlert. For now, the idea is firmly in the “what if” stage.
The U.S. Climate Prediction Center currently gives an 81% chance of a “very strong” El Niño by October–December, which raises the stakes for potential mitigation tools, per NOAA’s Climate Prediction Center. At the same time, the World Meteorological Organization notes there is no evidence that climate change has increased El Niño frequency or intensity, even though a warmer background climate can amplify the impacts of any given event. That caveat complicates how an intervention like cloud brightening might interact with long-term warming patterns, according to WMO.
Experts urge caution
Researchers and policy experts say that before anyone even contemplates a field test, the world would need robust multi-model comparisons, detailed regional impact studies, and international governance frameworks spelling out who decides when and how such tools might be used.
What comes next
The authors argue that their new study should motivate coordinated model intercomparisons and focused research on regional side effects and governance, rather than any rush to field experiments. The work is published in Science Advances (DOI 10.1126/sciadv.adx3012), and EurekAlert notes support from the National Science Foundation, NASA, the U.S. Department of Energy and NOAA.
For now, scientists frame marine cloud brightening as a possible future addition to flood control, seasonal forecasts and other risk-reduction tools, not as any kind of substitute for cutting greenhouse gas emissions. Turning down the sun a notch over one stretch of ocean, they argue, is no replacement for turning down the world’s fossil fuel use.
