Scientists investigate if brighter clouds could blunt deadly El Niño weather

As scientists warn that a powerful El Niño, a climate pattern pushing temperatures up, could develop in the coming years, new research suggests a controversial form of solar geoengineering might one day help reduce the natural occurence's most destructive impacts.

The study, published this week in Science Advances by researchers at the Scripps Institution of Oceanography and cited by CNN, examined whether marine cloud brightening—a technique designed to reflect more sunlight back into space—could lessen the intensity of extreme El Niño events.

El Niño is a naturally occurring climate pattern in the tropical Pacific Ocean that typically raises global temperatures and alters weather patterns around the world, increasing the likelihood of heatwaves, droughts, wildfires and flooding in many regions.

Scientists say human-driven climate change is amplifying these effects by raising the planet's baseline temperature, making strong El Niño events increasingly damaging.

Marine cloud brightening works by spraying tiny particles into low-lying marine clouds, making them more reflective so they bounce a greater share of the Sun's energy back into space. The resulting cooling effect could, in theory, weaken warming in the Pacific Ocean that drives El Niño.

Unusual research method

Because deliberately testing such geoengineering techniques in the real world could carry significant environmental risks, the researchers instead relied on what they described as a "natural experiment."

They analysed the aftermath of Australia's devastating 2019–20 "Black Summer" bushfires, which released vast amounts of smoke particles into the atmosphere. Earlier studies found those particles mixed with clouds over the Pacific Ocean, increasing their reflectivity and helping cool the ocean, potentially contributing to the La Niña conditions that followed.

Using climate models, the team isolated the cloud-brightening effect produced by the bushfire smoke and simulated what might have happened if a similar increase in cloud reflectivity had occurred before the major El Niño events of 1997 and 2015.

The models suggested that targeted marine cloud brightening could reduce the strength of El Niño while enhancing the cooling and drying conditions associated with La Niña by as much as 40 percent. The researchers also found the technique would likely be most effective if deployed early in an El Niño's development.

Despite the findings, the researchers stress that the work is theoretical and does not amount to a recommendation for deployment.

Conflicting views

Solar geoengineering remains one of the most controversial areas of climate science. Critics warn that deliberately altering Earth's climate could trigger unintended consequences that are difficult to predict and potentially impossible to reverse. Some also fear that once such interventions begin, they would need to continue indefinitely to avoid a rapid rebound in global temperatures—a phenomenon known as "termination shock."

Study co-author Kate Ricke, a climate scientist at Scripps Oceanography and the University of California San Diego's School of Global Policy and Strategy, said the approach examined in the study differs from proposals to cool the planet continuously.

Instead, she said, the idea would be to use geoengineering temporarily during exceptionally severe El Niño events that are expected to cause widespread damage.

"It’s not something that you're locking yourself into," Ricke said.

The researchers also acknowledged that weakening El Niño could have unintended regional consequences.

While El Niño causes trillions of dollars in global economic losses, some regions benefit from its effects. California, for example, often relies on the heavy rainfall associated with El Niño to replenish reservoirs after drought, even though those storms can also cause flooding and landslides.

Scientists say further research is needed to understand how marine cloud brightening could influence the timing, strength and frequency of subsequent La Niña events, as well as its impacts on different parts of the world.

"You have to think very carefully about trade-offs," Ricke said. Geoengineering "is probably best to think about for now in terms of super El Niños, where most people, most places are losers and really extreme, damaging events are most possible," she added.

By Nazrin Sadigova