Study Reveals How Clouds Keep the Earth Cool

A team of researchers has now shown how pollutants that end up in the atmosphere are associated with the cooling effect of bright clouds.

Clouds are mostly water droplets that have condensed on to small bits of pollutants in the air. When there is enough humidity, these particles aggregate, giving rise to brighter, bigger clouds. Now, these particles can be both natural and man-made, and most of them have volatile compounds that turn to vapor when the atmosphere is humid, according to a new release from The University of Manchester.

When conditions are cold and moist, these volatile compounds stay liquid and make large particles that lead to brighter clouds.

"We discovered that organic compounds such as those formed from forest emissions or from vehicle exhaust, affect the number of droplets in a cloud and hence its brightness, so affecting climate," said professor Gordon McFiggans, from the University of Manchester's School of Earth, Atmospheric and Environmental Sciences and one of the study authors.

"More cloud droplets lead to brighter cloud when viewed from above, reflecting more incoming sunlight. We did some calculations of the effects on climate and found that the cooling effect on global climate of the increase in cloud seed effectiveness is at least as great as the previously found entire uncertainty in the effect of pollution on clouds," McFiggans said in the news release.

The study is published in the journal Nature Geoscience.