New Delhi: Brightening low lying clouds over the eastern Pacific Ocean by spraying fine seawater droplets could potentially reduce the intensity of future super El Niño events, according to a new modelling study published in Science Advances. Researchers say the approach may help limit global temperature spikes and reduce the widespread economic and social impacts associated with extreme El Niño episodes, although significant uncertainties and potential regional risks remain.
El Niño is a naturally occurring climate phenomenon that develops when trade winds weaken, allowing warm surface waters to spread eastward across the Pacific Ocean. The resulting rise in sea surface temperatures influences weather patterns worldwide, often triggering droughts, floods, heatwaves and disruptions to agriculture and economies.
The proposed geoengineering technique, known as marine cloud brightening, involves spraying microscopic seawater droplets beneath low lying stratocumulus clouds. These droplets increase the number of cloud particles making clouds brighter and more reflective, allowing them to bounce more sunlight back into space and cool the ocean surface below.
Researchers suggest that cooling the Niño 3.4 region of the eastern Pacific could interrupt the chain of feedbacks that fuels El Niño. Lower sea surface temperatures would strengthen trade winds, pushing warm water back toward the western Pacific while encouraging the upwelling of cooler water, potentially preventing an El Niño from intensifying.
“We can basically stop the dominoes from falling early when we do marine cloud brightening,” said Jessica Wan of the University of California, San Diego, one of the study’s authors. “We’re kicking the cycle in the other direction.”
The idea was inspired by observations following Australia’s 2019-2020 “Black Summer” bushfires, when smoke particles drifting over the Pacific are believed to have brightened clouds, cooled ocean waters and contributed to a prolonged “triple-dip” La Niña event.
Using climate models the researchers simulated how marine cloud brightening might have affected the powerful El Niño events of 1997-98 and 2015-16. They found that spraying seawater over a nine month period could have reduced warming in the Niño 3.4 region from more than 2°C to just above 1°C, effectively turning a super El Niño into a moderate event and ending it several months earlier.
However implementing such a strategy would require an unprecedented operational effort. The study estimates that around 2,400 ships would be needed to continuously spray seawater using technology that is not yet capable of delivering the required volume of aerosol particles.
Scientists also caution that the findings are based on modelling and may not fully reflect real world climate behaviour. Mat Collins of the University of Exeter, who was not involved in the research, noted that warmer oceans can reduce low level cloud cover through feedback mechanisms potentially requiring even greater levels of aerosol injection than those modelled.
The researchers also found that weakening El Niño could unintentionally strengthen the following La Niña phase. In one simulation, La Niña developed earlier and became more intense which could have adverse consequences for regions such as the Horn of Africa where strong La Niña events have previously been linked to severe drought and food insecurity.
Despite these uncertainties, the authors argue that short term climate interventions targeting individual extreme events may carry fewer long term risks than continuous geoengineering schemes aimed at offsetting global warming. Unlike long duration solar radiation management, temporary cloud brightening may reduce concerns over “termination shock” the rapid warming that could occur if large scale geoengineering efforts were suddenly halted.
The researchers say further studies are needed to better understand the feasibility, effectiveness and potential unintended consequences of marine cloud brightening before any real world deployment is considered.