A new study by researchers from the University of Washington confirms that air pollution in the Northern Hemisphere can be held partly responsible for the African droughts in the 1980s.
Central Africa experienced decades of droughts, which reached its worst point in the 1980s. Lake Chad, used to water crops in neighboring countries nearly dried out completely, and poor agricultural practices and animal grazing were held responsible for this occurrence. However, a new study conducted by researchers from the University of Washington confirms that the Northern Hemisphere air pollution can be held partly responsible for the African droughts in the 1980s.
The pollutants emitted by coal-burning factories in the U.S. and Europe were responsible for shifting tropical rain bands to the South. Owing to this, the Sahel region was deprived of rain. However, when a clean-air policy was passed in the U.S., tropical rains stopped being shifted to the South. Now again, research has shown that owing to global warming, the Northern Hemisphere has begun to cool faster than the Southern Hemisphere, revising the previous trend.
This is the first study that used decades of historical observations to arrive a the conclusion that this drought was part of a global shift in tropical rainfall, and then used multiple climate models to determine why.
"One of our research strategies is to zoom out," said lead author Yen-Ting Hwang, a UW doctoral student in atmospheric sciences, said in a press release. "Instead of studying rainfall at a particular place, we try to look for the larger-scale patterns."
Researchers of the study looked at 26 climate models used by the Intergovernmental Panel on Climate Change and discovered that almost all the models also showed some southward shift and that cooling from sulfate aerosols in the Northern Hemisphere was the primary cause.
"We think people should know that these particles not only pollute air locally, but they also have these remote climate effects," Hwang said.
"To some extent, science messed this one up the first time around," said co-author Dargan Frierson, a UW associate professor of atmospheric sciences. "People thought that a large part of that drought was due to bad farming practices and desertification. But over the last 20 years or so we've realized that that was quite wrong, and that large-scale ocean and atmosphere patterns are significantly more powerful in terms of shaping where the rains fall."
The study concluded that the U.S. Clean Air Act and its European counterpart have had positive effects on the drought situation of Africa. While shorter-term droughts continue to affect the Sahel, the long-term drought began to recover in the 1980s.
