Biomass smoke coming from South Africa can help cool the Earth and counteract greenhouse effects that contribute to global warming.
More Reflective Clouds Can Cool Down Earth
Aerosols in the atmosphere can reflect sunlight away from Earth. Researchers now reveal that as biomass smoke from South Africa drifts over the southeast Atlantic Ocean, it significantly improves the brightness of low-level clouds and creates a reflective process that can cool down Earth.
Scientists have known that smoke can reduce the cooling effect of clouds by absorbing light supposedly reflected by the clouds beneath the aerosol.
In a new study, however, researchers discovered that smoke and cloud layers are closer to each other than what was believed earlier. It allows the clouds to be more reflective of light and capable of accelerating cooling effects.
Previous studies have shown that aerosols can disturb radiation in the top atmosphere by scattering and absorbing solar radiation as well as altering the cloud properties by changing the lower tropospheric stability.
Smoke During Fire Season
During the fire season of the year, which runs between July and October, wildfires and man-made fires intentionally set to clear farmland to produce biomass-burning aerosols that are emitted into the atmosphere. As the aerosols travel westward over the southeast Atlantic Ocean, they interact with the underlying stratocumulus cloud decks.
Using advanced computer models and satellite observations, Xiaohong Liu from the University of Wyoming and colleagues discovered that aerosols mixed into the clouds serve as cloud condensation nuclei, and increase the brightness of stratocumulus clouds, which can result in substantial cooling of our planet.
"We found the smoke comes down and can mix within the clouds," Liu said. "The changed clouds are more reflective of sunlight. Brighter clouds counteract the greenhouse effect. It creates cooling."
Liu and colleagues said that human-generated carbon monoxide causes a greenhouse effect of 1.66 watts per square meter uniformly distributed all over the globe. The fire smokes causes a much larger cooling effect of 7 watts per square meter over the southeast Atlantic ocean.
"Marine stratocumulus clouds cover nearly one-quarter of the ocean surface and thus play an extremely important role in determining the global radiative balance," the researchers wrote in their study published in the Proceedings of the National Academy of Sciences on March 5. "Our results highlight the importance of realistically representing the interactions of stratocumulus with biomass burning aerosols in global climate models in this region."