Scientists ponder a new climate defense tactic: Throwing shade at El Niño

Study Models Marine Cloud Brightening Effects on Historic El Niño Events

A study published Wednesday in Science Advances examines whether marine cloud brightening could reduce the intensity of El Niño events in model simulations. The research uses observations from the 2019-2020 Australian bushfires as a proxy for the technique’s regional effects.

El Niño occurs when trade winds weaken in the tropical Pacific, allowing warmer water to shift eastward toward South America. This phase typically raises global average temperatures and alters precipitation patterns, increasing drought risk in some areas and heavy rainfall in others. The current El Niño event has been described by monitoring agencies as potentially among the stronger episodes in recent decades.

The study’s authors, including Katherine Ricke of UC San Diego and the Scripps Institution of Oceanography, tested whether increasing the reflectivity of marine clouds over the Pacific could limit surface warming and thereby moderate El Niño development. Marine cloud brightening involves generating fine seawater droplets that, in principle, make low clouds more reflective. No large-scale field experiments of this method have been conducted; existing trials remain limited to small areas.

Because direct data on marine cloud brightening at scale do not exist, the researchers modeled the radiative effects observed during the Australian bushfire season. That event injected nearly one million metric tons of smoke into the stratosphere. Earlier analyses linked the smoke’s reflective particles to the subsequent development of a rare triple-dip La Niña, the cool phase opposite to El Niño. The team incorporated similar aerosol-driven reductions in incoming sunlight into climate model runs for two past El Niño episodes.

In those simulations, the imposed reduction in solar radiation reaching the ocean surface produced measurable decreases in the peak sea-surface temperature anomalies associated with the modeled El Niño events. The authors report corresponding reductions in some of the atmospheric circulation changes that typically accompany strong El Niño conditions.

Ricke described El Niño as a sensitive point in the climate system because temperature changes in the tropical Pacific influence atmospheric energy distribution on a global scale. She noted that the modeling exercise addressed a long-standing question about whether targeted regional interventions could affect large-scale modes such as El Niño.

The paper distinguishes this regional approach from earlier proposals for solar geoengineering that aim to offset global mean temperature rise through stratospheric aerosol injection. Marine cloud brightening, the authors argue, could in theory be applied over limited ocean areas rather than uniformly across the planet.

Andrew Dessler, a professor of atmospheric sciences at Texas A&M University who was not involved in the study, stated that the underlying physical reasoning appears consistent with current understanding of cloud-aerosol interactions. He added that practical implementation would face substantial governance and geopolitical obstacles, including the risk of unintended cross-border effects. Dessler emphasized that existing climate models contain uncertainties that could produce outcomes different from those simulated.

Ricke similarly cautioned that further modeling work is required before any real-world testing could be considered. She observed that interest in solar geoengineering research stems from scenarios in which conventional emissions reductions prove insufficient to limit climate impacts.

The study does not claim that marine cloud brightening has been demonstrated to work at scale or that it should be deployed. It presents results from one set of model experiments that used a specific natural analog for aerosol effects. Additional research would be needed to assess side effects on regional weather, ocean circulation, and precipitation outside the Pacific basin.