As carbon dioxide (CO 2 ) emissions continue to climb, interest in geoengineering is growing as governments, researchers, and environmental advocates search for ways to limit the worst effects of climate change. These large scale climate interventions could influence rainfall, agriculture, and ecosystems around the world, making their potential benefits and risks equally significant.
A new study from climate scientists at the University of California, Santa Barbara suggests that not all geoengineering strategies have the same consequences. While one proposed method could severely disrupt one of Earth's most important climate cycles, another appears to have little impact. The findings, published in Earth's Future , highlight why researchers say every proposal must be carefully evaluated before it is ever put into practice.
"We need to be careful about implementing geoengineering proposals before we fully understand what's going to happen," said first author Chen Xing, a doctoral student at UCSB's Bren School of Environmental Science & Management.
Xing and fellow Bren graduate student Cali Pfleger began the project to better understand how geoengineering might affect marine ecosystems. That question quickly led them to examine the El Niño Southern Oscillation (ENSO), a major driver of ocean and atmospheric conditions.
ENSO is a naturally occurring climate cycle that repeats every 2 to 7 years. It shifts warm ocean water across the tropical Pacific, influencing weather around the globe. During El Niño events, warmer waters move toward the west coasts of the Americas, often bringing wetter winters to California. During La Niña, warmer waters remain farther west, strengthening monsoon rains across parts of South and Southeast Asia.
Comparing Two Climate Cooling Strategies
The researchers studied two geoengineering approaches that aim to cool the planet by reflecting more sunlight back into space. Both rely on releasing tiny particles into the atmosphere, but they differ in the materials used and the altitude where they are released.
One method, known as marine cloud brightening (MCB), sprays sea salt particles less than 2 kilometers above the ocean surface. These particles create clouds with smaller, more numerous droplets, making the clouds brighter and more reflective.
The second method, called stratospheric aerosol injection (SAI), releases sulfate particles much higher in the atmosphere. Because these particles spread more evenly around the globe, they block a portion of incoming sunlight over a much larger area.
Marine cloud brightening has often been proposed for the eastern sides of ocean basins because of its strong cooling potential. However, the southeastern Pacific also plays an important role in maintaining ENSO.
The simulations revealed an unexpected result. "Deploying MCB in the subtropical eastern Pacific dramatically reduces ENSO amplitude by approximately 61%," the authors write.
"It's hard to get ENSO to change by that much that quickly," said Associate Professor Samantha Stevenson, who co-authored the study, and is Xing's and Pfleger's advisor.
The reason lies in how marine cloud brightening changes local weather. Brighter clouds cool the ocean surface below while also reducing rainfall because the smaller cloud droplets are less likely to combine into raindrops. As cooler, drier air spreads into the central Pacific, evaporation decreases, atmospheric circulation weakens, and winds along th...