‘Cloud brightening’ won’t have effect many are hoping for, scientists say

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Clouds form when water vapor condenses around particles in the atmosphere. Some scientists have speculated that fossil fuel emissions and other types of air pollution will help seed bigger, brighter clouds — clouds that will reflect sunlight and slow global warming.

However, new research suggests the phenomenon known as “cloud brightening” is likely to be counteracted by sea salt.

By studying cloud formation in the pollution-free skies above the Southern Ocean, scientists were able to identify an inverse relationship between sea salt availability and sulfate aerosols.

“Greater sea-spray nuclei availability mostly suppresses sulfate aerosol activation leading to an overall decrease in cloud droplet concentrations,” researchers wrote in their paper on the topic, newly published in the journal Climate and Atmospheric Science.

In other words, the presence of sea salt is likely to diminish the ability of pollution particles to seed and brighten clouds.

“This means that recent theories that increased sulphate production can decrease the impact of climate change need to be reconsidered,” researcher Colin O’Dowd, professor of atmospheric physics at the National University of Ireland Galway, said in a news release. “Science is clearly pointing to the fact that carbon-based human activity is hurting our environment and there’s only one pathway to solve this — less fossil fuel and no interference with nature.”

In addition to smothering the hopes of supporters of climate engineering efforts, the latest research could help climate scientists produce more accurate prediction models.

“Clouds, particularly those overlying dark ocean surfaces, are the Earth’s key climate regulators, accounting for half of global reflectance,” said lead study author Kirsten Fossum, postdoctoral researcher at NUI Galway.

“Pollution-induced changes to cloud reflectance, represent the single biggest uncertainty in predicting future climate change,” Fossum said. “The large area covered and systematic evidence from the cruise to Antarctica provided the vast sample of clean air needed to conclusively support this study.”

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