UCSD - University of California - San Diego

07/08/2026 | Press release | Distributed by Public on 07/08/2026 12:07

Could Geoengineering Work to Tamp Down Super El Niños

Published Date

July 08, 2026

Article Content

Key Takeaways

  • A 2019 Australian bushfire provided a rare opportunity to scientists by creating an effect analogous to what could be achieved through the geoengineering technique known as marine cloud brightening.
  • A team of researchers used model simulations to reveal that if the 2019 brightening event occurred at different times in history instead, marine cloud brightening could weaken individual strong El Niño events.

With an anticipated "super" El Niño looming, a new study led by UC San Diego's Scripps Institution of Oceanography considers whether society could use a weather-altering technique as a tool to mitigate the floods, extreme heat and other events that El Niño would bring.

An attempted real-world field test could lead to disastrous unintended consequences but the "Black Summer" bushfires that scorched Australia in 2019 and 2020 served as a "natural experiment." The smoke that wafted into the atmosphere was filled with reflective, cloud interacting aerosols akin to those used in a geoengineering method called marine cloud brightening.

Previous research by one of the study co-authors found that the smoke-brightened clouds throughout the southeastern Pacific Ocean appeared to play a key role in creating global La Niña-like weather patterns. The effect was compelling enough that the team led by Scripps Oceanography researchers Kate Ricke and Jessica Wan used a seasonal forecasting model to investigate what would have happened if a similar event had occurred before a "super El Niño" instead. The results suggest that this might be an instance where geoengineering is worthy of serious consideration, the authors said.

"As long-term anthropogenic warming and short-term natural variability often compound to produce extreme weather events, our findings suggest it may be worth considering interventions which target natural variability, rather than the forced response to greenhouse gases," said the authors in the study released July 8 in the journal Science Advances. "Such an approach could result in similar physical risk reduction with shorter duration interventions that carry less sociotechnical risk than a sustained deployment."

The study appears July 8 in the journal Science Advances.

Geoengineering - the altering of climate by making clouds brighter, the oceans more greenhouse gas-absorbent or other means - has been proffered as a solution to slow the pace of global warming for decades but is always accompanied by controversy. Scientists and environmental agencies cite the potential for such methods to make things worse in ways not easily predicted. Entrepreneurs seeking to build a new industry have pushed for real-world testing and have quietly done so in a few regions of the world.

Ricke, a climate scientist with appointments at Scripps Oceanography and UC San Diego's School of Global Policy and Strategy, is usually firmly in the camp of scientists who urge caution, saying much more research needs to be done to make an adequate risk/reward analysis. This case is not ordinary, she said. Applied to El Niños like the one forming now, geoengineering could be used temporarily as a tool to help society mitigate specific events nearly guaranteed to produce significant damage. Economic analyses have shown that recent large El Niños cost society trillions of dollars in damage, the authors note.

Strategic marine cloud brightening could be added to an arsenal that already includes flood control and other measures.

The rapid-response nature of such an intervention contrasts with geoengineering schemes that address human-caused global warming but entail a need for international cooperation to manage them over years or decades, Ricke and Wan said.

"One of the biggest social concerns around geoengineering is the fact that if we use it to reduce long-term climate risks, we have to deploy it continuously for an indefinite period of time," said Wan, now a postdoctoral researcher at the University of Chicago who performed the research while she was a graduate student in Ricke's lab. "If we could target natural variability, we could get some of the benefits of geoengineering without having to employ it indefinitely."

Ricke and Wan say this analysis wouldn't have been possible without a 2023 study led by John Fasullo of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado. (Fasullo is also a co-author of this paper.) Fasullo's team charted the effects of the bushfire smoke that mixed with clouds over the southeastern Pacific Ocean. Another research team had earlier found that the fires emitted a record-breaking amount of aerosols, an effect on par to that from volcanic eruptions.

The reflective particles in that smoke brightened the clouds, increasing the amount of solar radiation bouncing back to space and altering the atmosphere's circulation, lessening how much El Niño-fueling heat made it to the lower atmosphere. The team also found that it enhanced the La Niña that formed in 2020.

"It was the key breakthrough to this becoming a viable research question," said Ricke. "Without that validation opportunity, I don't think our findings would be so credible."

The team modeled what would happen if - instead of "natural" cloud brightening from smoke during La Niña - deliberate marine cloud brightening were deployed in the Southeast Pacific during major El Niños that originated in 2015 and 1997. The simulation suggested that the targeted marine cloud brightening would indeed attenuate its effects, becoming more effective the earlier in the El Niño event they were introduced. If deployed over the central Pacific Ocean, marine cloud brightening could increase the cooling and drying effects associated with La Niña by more than 40%.

The researchers said they are not aware of any proposals to test this on the El Niño brewing now, but as research progresses, actual geoengineering schemes could be considered by government-level decision makers in the future.

"It's a different way of thinking about geoengineering," said Ricke. "We need to understand a lot more, but if there is a way to use this in addition to the risk reduction tools to mitigate El Niños, why wouldn't we consider it?"

Besides Wan, Ricke and Fasullo, study co-authors are Nan Rosenbloom and Chih-Chieh Chen of NCAR.

The National Science Foundation, NASA, the U.S. Department of Energy and NOAA supported the research.

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