 |
| El Niño represented by sea surface height in June 2026. Image Credit: NASA |
Scientific Frontline: Extended "At a Glance" Summary: Targeted Marine Cloud Brightening
The Core Concept: Targeted marine cloud brightening is a short-term geoengineering intervention designed to weaken the extreme weather impacts of "super" El Niño events by increasing the reflectivity of oceanic cloud cover.
Key Distinction/Mechanism: Unlike long-term geoengineering schemes meant to continuously offset human-caused greenhouse gas warming, this method targets short-term natural climate variability. By injecting reflective aerosols into clouds over the Pacific Ocean, the intervention bounces incoming solar radiation back into space, thereby cooling the lower atmosphere and diminishing the heat that fuels El Niño patterns.
Origin/History: The viability of this concept was validated by a "natural experiment" during the 2019–2020 "Black Summer" Australian bushfires. Record-breaking aerosol emissions from the fires mixed with clouds over the southeastern Pacific Ocean, artificially brightening them and enhancing a global La Niña event.
Major Frameworks/Components:
- Marine cloud brightening (MCB): The deliberate introduction of reflective aerosols to manipulate cloud albedo.
- Aerosol-cloud interactions: The physical mechanism where particulate matter increases water droplet nucleation, resulting in increased solar reflection.
- Seasonal climate modeling: The use of predictive simulations, specifically modeling hypothetical interventions during historical super El Niños (such as the 1997 and 2015 events), to evaluate efficacy.
- Short-term targeted deployment: A strategic framework minimizing the sociotechnical risks associated with indefinite, sustained geoengineering deployments.
Branch of Science: Atmospheric Science, Climatology, Meteorology, and Oceanography.
Future Application: Government agencies could deploy strategic marine cloud brightening as a temporary, rapid-response tool, alongside traditional flood control measures, to mitigate the severe heat, flooding, and infrastructure damage anticipated from brewing super El Niños.
Why It Matters: El Niño events frequently cause trillions of dollars in global economic damage. Targeted geoengineering offers a method to substantially reduce these immediate physical risks without the need for the continuous, indefinite deployment required by broader climate change mitigation strategies.
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 coauthors 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 that target natural variability, rather than the forced response to greenhouse gases,” the authors noted 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.”
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 Niño events 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 Niño events 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 coauthor 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 with that from volcanic eruptions.
The reflective particles in that smoke brightened the clouds, increasing the amount of solar radiation bouncing back to space, altering the atmosphere's circulation, and 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 Niño events that originated in 2015 and 1997. The simulation suggested that the targeted marine cloud brightening would indeed attenuate the events' effects, becoming more effective the earlier it was 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 Niño events, why wouldn’t we consider it?”
Funding: The National Science Foundation, NASA, the US Department of Energy, and NOAA supported the research.
Published in journal: Science Advances
Title: Targeted marine cloud brightening weakens subsequent El Niño
Authors: Jessica S. Wan, John T. Fasullo, Nan Rosenbloom, Chih-Chieh Chen, and Katharine Ricke
Source/Credit: University of California, San Diego | Robert Monroe
Edited by: Scientific Frontline
Reference Number: as070926_01
.jpg)