From a beach or the deck of a ship, marine stratocumulus clouds don’t look like anything special. Quite frankly, they’re too big—often stretching for hundreds of miles—for us to appreciate from below. We see only a fraction of a formation, a lumpy or ripply blanket draped across the sky, from our typical puny human vantage. It’s only from far above, thanks to satellite imagery, that their shifting patterns of light and dark catch the eye.
Climate scientists have been keeping close watch on these formations for years, because of the role they play in global climate and what they can reveal about hyperlocal environmental conditions.
On any given day, almost a quarter of Earth’s oceans are covered with marine stratocumulus clouds—they’re one of the most common kinds of cloud moving through the atmosphere. You’ll find them primarily along western coasts in the mid- to lower latitudes, where upwelling occurs. That’s when Earth’s rotation can push warm surface water away from the coast, bringing cold water surging up from the depths. This chilly water cools the air above it, ultimately leading to these low-lying clouds, which are roughly a mile above the surface. And that’s when things get interesting.
The clouds organize into open- or closed-cell formations; the latter, as you might imagine, is denser and puffier, and the sun’s radiation largely bounces off it. These closed-cell marine stratocumulus clouds essentially shade the planet, cooling off the surface by reflecting sunlight back into space.
Open-cell marine stratocumulus clouds, on the other hand, are thin and ethereal, with an open center that allows the sun to shine through and hit the surface of the planet, heating it up. They also tend to break up faster, unlike their closed-cell cousins, which can stick around for the better part of a day—for now.
In 2019, a Nature Geoscience paper showed that, in simulations, high concentrations of greenhouse gases caused closed-cell marine stratocumulus clouds to break up and not re-form. This exposed more of Earth’s surface to the sun, which increased warming. The levels of carbon dioxide used in the simulations were considerably higher than they are on Earth today—1,200 parts per million, or about three times current levels—and the authors considered the results preliminary. But the research hints at the importance of keeping these common clouds around. As a result, marine stratocumulus clouds are among the most closely studied types of cloud.
Even on a local scale, marine stratocumulus clouds are sensitive to environmental changes. Papers in the Journal of Geophysical Research and other peer-reviewed journals found that emissions from ships chugging across the oceans, as well as pollutants, smoke from wildfires, sand from dust storms, and other matter that gets released into the atmosphere all affect whether the clouds are open- or closed-cell.
Speaking of things getting released into the atmosphere, if you’re along the Southern California coast and see something big and white floating by, don’t assume it’s a spy balloon. In February, researchers from UC-San Diego’s Scripps Institute and the Department of Energy began a yearlong project that includes plans to release four weather balloons each day to study marine stratocumulus clouds in real time. It’s just the latest effort to understand how these clouds may be critical for climate control—and canaries in the coal mine for changes in global patterns.