Plankton Make Clouds Brighter and the Earth Cooler

Plankton, the tiny organisms that drift through the ocean (plotting to take over the world, if SpongeBob Squarepants is to be believed), may play a vital role in keeping the Earth cool. A new study from the University of Washington and the Pacific Northwest National Laboratory finds that gases produced by plankton in the Southern Hemisphere create brighter clouds, reflecting sunlight.

The study, published in the journal Science Advances, found that clouds in the Southern Hemisphere are composed of smaller droplets in the summer, making them brighter than they would be otherwise. (Cloud reflectivity is based on both the amount of liquid they contain and the size of the droplets that liquid is spread across.)

A phytoplankton bloom off the coast of Alaska. Image Credit: NASA's Goddard Space Flight Center, Norman Kuring; USGS

Plankton double the concentration of water droplets in clouds in the summer, when phytoplankton bloom in the southern half of the world, according to the study. The tiny organisms produce gases like dimethyl sulfide that can seed cloud droplets, which form from aerosols. Caught up in sea spray, small particles of organic matter from plankton can also make their way into clouds, where they can absorb light. Over the course of the year, the increased brightness associated with these denser cloud droplets reflects an estimated 0.37 watts of solar energy per square foot of cloud. Meaning without plankton, the Earth would be even warmer.

Image Credit: Daniel McCoy / University of Washington

This adds to previous research showing that plankton are important climate mediators in the Southern Hemisphere. In the global north, however, their role is less understood, since there are more interfering aerosols from forests and pollution, among other factors.