Aerosols have a bigger impact on cloud cover than expected

Aerosols are tiny particles suspended in the atmosphere, which play a fundamental role in the formation of clouds. With aerosols significantly increasing due to human activities, many assessments of the Intergovernmental Panel on Climate Change (IPCC) have suggested that these particles could have an important impact on climate change because clouds reflect sunlight and maintain lower temperatures. 

A new study led by the University of Exeter has found that aerosol particles in the atmosphere have a bigger impact on cloud cover than previously thought, but less effect on cloud brightness.

The scientists used 20 years of satellite cloud images from two different satellite platforms to compare the periods before and after the 2014 volcanic eruption from Iceland. 

“This massive aerosol plume in an otherwise near-pristine environment provided an ideal natural experiment to quantify cloud responses to aerosol changes, namely the aerosol’s fingerprint on clouds,” said study lead author Ying Chen, an expert in aerosol-cloud-climate interactions at the University of Exeter.

“Our analysis shows that aerosols from the eruption increased cloud cover by approximately ten percent. Based on these findings, we can see that more than 60 percent of the climate cooling effect of cloud-aerosol interactions is caused by increased cloud cover. Volcanic aerosols also brightened clouds by reducing water droplet size, but this had a significantly smaller impact than cloud-cover changes in reflecting solar radiation.”

While previous models and observations suggested that cloud brightening accounted for the majority of cooling caused by cloud-aerosols interaction, this study sheds new light on the complex – and sometimes unexpected – ways in which these particles interact with the climate.

 “Our earlier work had showed that model simulations could be used to disentangle the relative contribution of aerosol-cloud-climate impacts and potentially confounding meteorological variability,” said study co-author Jim Haywood, a professor of Atmospheric Science at Exeter.

“This work is radically different as it does not rely on models; it uses state-of-the-art machine learning techniques applied to satellite observations to simulate what the cloud would look like in the absence of the aerosols. Clear differences are observed between the predicted and observed cloud properties which can be used to assess aerosol-cloud-climate impacts,” he concluded.

The study is published in the journal Nature Geoscience.

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By Andrei Ionescu, Earth.com Staff Writer