Research and Application News
UMBC physicists discover unexpected effect of African wildfires on climate
05 March 2018
Clouds play a prominent role in moderating Earth's climate, but their role is still poorly understood. Generally, clouds cool the Earth by reflecting incoming sunlight back out into space. Reducing the clouds' reflectivity—with a layer of pollution, for example—reduces the cooling effect. However, new research in Proceedings of the National Academy of Sciences by Zhibo Zhang, associate professor of atmospheric physics at UMBC, two of his students, and collaborators from University of Wyoming, University of Science and Technology of China, Universities Space Research Association, and University of Michigan adds another level of complexity to this model.
Every fall, fires race across central and southern Africa. Many are wildfires; others are intentionally set by humans to clear farmland. They create so much smoke that it's clearly visible from space. Wind sweeps the smoke westward over the Atlantic Ocean, where it rises above the largest semi-permanent gathering of clouds in the world. For years, scientists believed that overall, the smoke diminishes the clouds' cooling effect by absorbing light that the clouds beneath otherwise would reflect. The new study by Zhang and colleagues doesn't dispute the existence of this effect, but introduces a new mechanism that counteracts it by making the clouds more reflective.
Image credit: NASA/Kirk Knobelspiesse - View from a data-collecting aircraft over the Atlantic Ocean, where a layer of smoke is visible above the clouds.