Impacts of Mesoscale Cloud Patterns on Climate

What is it about?

Shallow clouds in the trade-wind regions help cool the Earth by reflecting sunlight back into space. Today’s global climate models cannot directly represent these small clouds because their resolution is too coarse, so they typically assume the clouds only respond to large-scale weather patterns spanning more than 1,000 kilometers. However, satellite images show that these clouds consistently form distinctive “mesoscale” patterns over distances of tens to a few hundred kilometers. In this study, we show, for the first time, that the interplay between the processes shaping these mesoscale cloud patterns can influence the Earth’s energy balance even when the large-scale conditions are controlled for.

Featured Image

Photo by Flavius Floare on Unsplash

Photo by Flavius Floare on Unsplash

Why is it important?

Clouds—especially shallow clouds—have been one of the largest sources of uncertainty in climate projections since the earliest climate models in the 1990s. Trade-wind cumulus clouds are one important type of shallow cloud. Their formation depends on processes that span an enormous range of scales: from tiny droplets only tens of microns across, to individual clouds several kilometers wide, all the way up to weather systems larger than 1,000 kilometers. Satellite images consistently show that these shallow clouds form organized patterns at “mesoscales,” meaning tens to a few hundred kilometers. High-resolution atmospheric models also confirm that these mesoscale patterns arise from the clouds’ own internal dynamics—not just from large-scale weather. Because global climate models are too coarse to represent these mesoscale processes, they may miss an important piece of how shallow clouds behave. This leads to a key open question in climate science: Would representing mesoscale cloud organization in climate models change their estimates of cloud feedback, and help reduce the long-standing uncertainty in how clouds influence future climate? In this paper, we show that mesoscale processes have a substantial influence on how warm or cool the current climate is—an influence that is comparable to that of large-scale conditions. Surprisingly, even when the large-scale environment is kept the same, mesoscale processes affect the climate not by changing how much sunlight the clouds reflect, but by altering the amount of water vapor—a key greenhouse gas—in the upper parts of the cloud layer. This suggests that mesoscale processes can influence the larger-scale climate system, and may therefore play a role in shaping cloud–climate feedbacks.