Scientists are exploring the potential of a geoengineering technique known as marine cloud brightening to mitigate the effects of El Niño, a natural climate pattern that disrupts global weather and causes significant economic damage. New research from the University of California, San Diego suggests that increasing the reflectivity of marine clouds over the southeast Pacific Ocean at the onset and during the growth phase of El Niño could weaken the event’s intensity.

El Niño is characterized by warmer-than-average sea surface temperatures in the central and eastern tropical Pacific Ocean. This phenomenon, part of the broader El Niño-Southern Oscillation (ENSO) cycle, impacts weather patterns worldwide, often leading to extreme weather such as droughts, floods, and storms. The study, published in Science Advances, examined whether targeted cloud brightening could disrupt the ocean-atmosphere feedback mechanisms that lead to El Niño’s development.

Marine cloud brightening involves injecting aerosols—tiny particles such as sea salt—into the lower atmosphere to enhance the reflectivity of marine clouds. These brighter clouds reflect more sunlight back into space, reducing heat absorption by the ocean surface. By cooling these critical ocean areas, researchers believe they can prevent or dampen the progression of El Niño events.

Lead author Jessica Wan, a postdoctoral researcher at the University of Chicago who conducted the study while at UC San Diego, noted that targeting natural climate variability like El Niño could achieve some benefits of geoengineering without requiring continuous deployment. Study coauthor Kate Ricke explained that this approach cools ocean temperatures in regions instrumental to the ocean-atmosphere feedback loops fostering El Niño, effectively shifting the Pacific back to a neutral or La Niña state, which is characterized by cooler ocean temperatures and typically brings different weather patterns.

The concept draws partial support from observations of the 2019-2020 Australian bushfires, which released aerosols that brightened marine clouds over the southeast Pacific. Researchers treated this event as a “natural experiment,” finding that the cloud-brightening effects may have contributed to the Pacific's transition to a La Niña phase following the fires.

Model simulations of major El Niño events in 1997 and 2015 showed that early deployment of marine cloud brightening could substantially reduce El Niño’s intensity. If applied over the central Pacific, the approach might even amplify La Niña’s cooling and drying effects by over 40%.

Despite promising modeling results, significant challenges remain before marine cloud brightening can be considered a feasible intervention. David Keith, a climate systems engineering specialist at the University of Chicago not involved in the study, emphasized that the technology necessary to produce the aerosol sprays does not yet exist and would require substantial innovation. However, he noted that related solar reflection approaches, like injecting sulfur into the stratosphere, could be implemented with current technology.

Experts also caution about the uncertainties and potential risks linked to geoengineering. Holly Buck from the University at Buffalo highlighted that the ecological impacts of marine cloud brightening remain poorly understood, especially the possibility of unintended climate effects in distant regions.

The UC San Diego researchers acknowledge that no proposals are currently underway to test marine cloud brightening against the developing El Niño event. Nevertheless, as understanding advances, the technique could enter consideration by policymakers seeking novel strategies to manage extreme climate variability.