Improving the ability to predict influence of aerosols on cloud cover

NASA/Goddard Space Flight Center: Using a novel theoretical approach, researchers from NASA and other institutions have identified the common thread that determines how aerosols from human activity, like the particles from burning of vegetation and forests, influence cloud cover and ultimately affect climate. The study improves researchers’ ability to predict whether aerosols will increase or decrease cloud cover.

“We connected the dots to draw a critical conclusion, and found evidence over the Amazon that traces the direct path of the effect of human activity on climate change by way of human-caused aerosols,” said study co-author Lorraine Remer, a physical scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “During the dry season in the Amazon, the only aerosols of any magnitude are from smoke emerging from human-initiated fires.”

It is well documented from previous studies that aerosols play an essential role in how clouds develop. With this knowledge, a team comprised of Remer, Ilan Koren of the Weizmann Institute in Rehovot, Israel and J. Vanderlei Martins of the University of Maryland Baltimore County set out to explore one of the least understood but most significant aspects of climate change caused by human activity: the connection between a change in the amount of human-caused aerosols and change in the structure of clouds. Findings from their study will be published tomorrow in the journal Science.

“Scientists have observed instances where increases or decreases in the amount of these tiny particles have increased and decreased cloud cover in different places and times,” said Remer. “We saw an example of this ourselves: increased aerosols over the Amazon produced less cloud cover. Over the Atlantic Ocean, however, increased aerosols actually produced more cloud cover. We wanted to know what the link was between these different outcomes from varying amounts and types of aerosols. This paper gives us a clear picture of what is occurring.”

The team developed an analytical model, or line of thinking that combined knowledge of cloud development, satellite observations and mathematical calculations of aerosol concentration and cloud properties in an effort to explain how the two opposing effects of aerosols on clouds can influence cloud coverage and life cycle.

“This result helps us understand aerosols’ effect on a cloud’s mass and lifetime -- how long it will provide cloud cover, how deep the clouds will be, and when and where it will rain,” said Remer. “This improved understanding leads to prediction and prediction can help us plan and perhaps prevent some of the potential consequences of putting aerosols from human activity into the atmosphere.”….

Clouds rise through smoke over the Amazon. During the dry season, smoke covers wide swaths of the Amazon. Isolated towers of cumulus clouds poke through the dense layer of smoke in this photograph taken from an airplane in 2005. Credit: Ilan Koren, Weismann Instutute, from the NASA/Goddard website