Marine Cloud Brightening in Southeastern Pacific Cuts ENSO Amplitude 61 Percent in UCSB Simulations

The study published in Earth's Future used CESM2 simulations to compare marine cloud brightening with stratospheric aerosol injection. MCB applied over the southeastern Pacific cooled local sea surface temperatures and suppressed rainfall, which propagated westward and intensified the Walker circulation. This feedback loop stabilized the tropical Pacific, sharply damping both El Niño and La Niña extremes. SAI produced far smaller ENSO changes because its aerosols were released at higher altitudes and dispersed more uniformly.

ENSO drives global precipitation and temperature anomalies that affect agriculture from California to Southeast Asia. A 61 percent amplitude drop would alter monsoon timing and intensity, potentially reducing rice yields in Indonesia while shifting drought risk in the Amazon. The authors note that current governance discussions focus on global mean temperature targets and rarely model regional circulation feedbacks at this resolution.

Existing IPCC assessments flag geoengineering uncertainties but lack high-resolution ENSO experiments for MCB. Real-world deployment would require continuous ocean-atmosphere monitoring arrays across the Pacific that do not yet exist at the needed density. Without them, early warning of circulation shifts would arrive only after impacts on fisheries and rainfall had begun.

Policy timelines now include small-scale MCB field trials proposed for 2027-2030 in the same southeastern Pacific region identified as high-risk. Embedding ENSO diagnostics into those trials offers the clearest path to test whether the modeled damping occurs outside idealized simulations.