Researchers have found that marine cloud brightening (MCB)—injecting aerosols into the atmosphere to reflect sunlight—can reduce the intensity of El Niño events, according to a study published July 8 in Science Advances. By brightening clouds over the eastern subtropical Pacific, scientists simulated a cooling effect that could mitigate the extreme weather associated with these climate patterns.
How Marine Cloud Brightening Influences El Niño
Marine cloud brightening works by injecting aerosols, specifically sea salts, into the atmosphere. These particles make clouds whiter and more reflective, sending more solar radiation back into space. According to the study led by Jessica Wan, a climate scientist at the University of Chicago, targeting the eastern subtropical Pacific can trigger atmospheric changes that weaken the “warm” phase of the El Niño–Southern Oscillation.
The research was inspired by a natural occurrence during the 2019–2020 Australian wildfires. Wan, who conducted the research while at the Scripps Institution of Oceanography, observed that massive plumes of smoke particles drifted over the southeastern subtropical Pacific. These particles brightened the clouds, which helped trigger a multiyear La Niña event—the flip side to an El Niño.
Simulation Results from 1997 and 2015 Events
To test the viability of geoengineering, the team used computer simulations to revisit two strong El Niño events: 1997–1998 and 2015–2016. They simulated a high concentration of aerosol injections—approximately 500 particles per cubic centimeter—in the regions where wildfire particles had previously been densest.
The simulations revealed that the timing of the intervention is critical to its success:
- Early Intervention: For the 2015–2016 event, injecting particles from June through the following February produced the strongest cooling effect.
- Late Intervention: Starting injections in December resulted in the least cooling, as the El Niño dynamics were already well under way.
By April 2016, the simulated sea surface temperatures were significantly cooler than the actual real-world conditions recorded during that event, according to the research data.
Risks and Geoengineering Constraints
Despite the simulated success, climate scientists warn that tinkering with the atmosphere carries significant risks. James Haywood, a climate scientist at the University of Exeter, noted that previous simulations of MCB suggested that cooling the eastern Pacific might produce a “mega La Niña” many times stronger than previously seen.
While El Niño is often viewed as the more destructive phase, Wan notes that the impacts of both El Niño and La Niña are “heterogeneous” across the planet. A cooling effect that benefits one region may cause severe weather or drought in another.
Daniele Visioni, a climate scientist at Cornell University, stated that while this is not a final answer, the study indicates that the concept is “worth thinking about” given the damage caused by large El Niño events.
Current Implementation Status
Though the Earth entered its most recent El Niño phase in June, MCB is not currently being deployed. Wan cited several major hurdles preventing immediate use, including engineering constraints and sociological barriers. A primary concern remains the governance of such technology—specifically, who should determine whether these interventions are worth any possible negative climate consequences.
| Feature | El Niño (Warm Phase) | La Niña (Cool Phase) |
|---|---|---|
| Ocean Temp | Above average in Central/Eastern Pacific | Below average in Central/Eastern Pacific |
| Typical Effects | Heat waves, torrential rains, severe droughts | Generally cooler temperatures, milder weather |
| MCB Goal | Cool the surface to reduce intensity | (Potential risk of over-strengthening) |
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