How clouds form and how they help set the temperature of the earth are two of the big remaining questions in climate research. Now, a study of clouds over the world’s remotest ocean shows that ocean life is responsible for up to half the cloud droplets that pop in and out of existence during summer.
The study, which appears online July 17 in Science Advances, combines computer modeling with satellite data over the Southern Ocean, the vast sea surrounding Antarctica. It reveals how tiny natural particles given off by marine organisms — airborne droplets and solid particles called aerosols — nearly double cloud droplet numbers in the summer, which boosts the amount of sunlight reflected back to space. And for the first time, this study estimates how much solar energy that equates to over the whole Southern Ocean.
“It is a strong effect,” said climate scientist Susannah Burrows at the Department of Energy’s Pacific Northwest National Laboratory. “But it makes sense because most of the area down there is ocean, with strong winds that kick up a lot of spray and lots of marine microorganisms producing these particles. And continental aerosol sources are mostly so far away that they only have a limited impact. Really the marine aerosols are running the show there.”
Burrows and co-author Daniel McCoy at the University of Washington worked with other colleagues from the University of Leeds, Los Alamos National Laboratory, UW and PNNL to explore the atmospheric show-runners.
Ocean born
Although the Southern Ocean’s borders have yet to be settled on by the International Hydrographic Organization, it comprises the southernmost parts of the Atlantic, Pacific and Indian Oceans, and is one of the cloudiest places on Earth. Important to the Southern Hemisphere’s atmospheric and oceanic circulation, Southern Ocean clouds might also help determine how sensitive Earth is to the accumulation of greenhouse gases in its atmosphere.
But to understand that climate sensitivity, scientists need to improve their understanding of how tiny aerosol particles brighten clouds by serving as seeds for cloud droplets. Over land, aerosols arise from vegetative matter, pollution, and dust. Sea spray shoots sea salt — a large source of ocean aerosols — into the atmosphere, but marine organisms also produce aerosols, most of which evaporate into the air.
But studying marine aerosols has been hard because they get overpowered by man-made pollutants in measurements near coastlines. Even so, studying marine aerosols in the Southern Ocean has been difficult as well.
Continue reading at Pacific Northwest National Laboratory.
Cloud image via Shutterstock.