A climate-modeling study published in Science Advances argues that reflecting more sunlight away from parts of the Pacific could reduce the severity of future El Niño events. The proposal is not a deployment plan. It is a model result, and the usual geoengineering caveats are doing a lot of work here.
The study’s authors, including Katherine Ricke of UC San Diego and the Scripps Institution of Oceanography, examined marine cloud brightening, a solar geoengineering technique that would spray seawater into low marine clouds so they reflect more incoming sunlight. The idea is to cool the ocean surface in a targeted region rather than try to shade the whole planet.
El Niño forms every few years in the tropical Pacific when trade winds weaken and warm ocean water shifts eastward toward South America. That ocean rearrangement can raise average global temperatures and change weather patterns far from the Pacific, including drought in some regions, heavier rain and flooding in others, and more cyclones in the Pacific. Against the background of fossil-fuel-driven warming, a strong El Niño can produce economic losses in the hundreds of billions, according to the study discussion reported by Wired.
Ricke described El Niño as a climate lever with global reach. “El Niño is one of these things where something happens in the tropical Pacific, and then it rearranges the way the entire global atmosphere is holding energy that year,” she said. “It’s an ultimate pressure point in the climate system.”
Marine cloud brightening remains mostly theoretical at climate-relevant scale. Some pilot projects and randomized controlled trials have tested pieces of the method, but only at small scale. Other solar geoengineering concepts, such as injecting aerosols into the stratosphere from aircraft, are generally discussed as global interventions. The attraction of marine cloud brightening, in this study, is its possible regional use.
Because researchers do not have large real-world marine cloud brightening experiments to analyze, Ricke’s team looked to a messy natural analog: Australia’s 2019-2020 bushfire season. More than 10,000 fires burned across the country and produced almost 1 million metric tons of smoke, one of the largest smoke injections into the stratosphere observed by satellites. Prior research found that reflective particles from that smoke helped contribute to a rare three-year La Niña, the cool counterpart to El Niño.
The researchers then built a model using the sunlight-reflecting effect associated with that event and tested it against two past El Niño episodes. Their simulations found that reducing sunlight reaching the Pacific surface would have significantly lowered the strength of those El Niño events and reduced their global effects.
The political and scientific warning labels are not small print. Geoengineering has drawn sustained criticism because climate systems do not respond like tidy lab equipment, and interventions that change weather can create losers as well as winners. Andrew Dessler, an atmospheric science professor at Texas A&M University, told Wired that the study’s argument “seems quite reasonable,” while calling real-world deployment “a political nightmare.”
Dessler also warned that model error is not a footnote. “These models are imperfect, and there's the possibility that you'll create an unpredicted problem that is worse than the problem you're trying to solve,” he said. He added that the paper was interesting, but said he would not treat it as a reason to implement the idea.
Ricke also said more modeling is needed before any real-world attempt. Her rationale for studying solar geoengineering is conditional and grim: if fossil fuel pollution is not cut enough, researchers may face a future in which such tools are considered. That is a research argument, not a permission slip.
This story draws on original reporting from WIRED.
