Starting in the 1960s, the rainfall band shifted southward, drying out Central Africa and parts of South America and South Asia, the study found. At the same time, northeast Brazil and Africa's Great Lakes started to see more rain, thanks to the southerly drift.
The team modeled the reasons for the changing tropical rainfall with all 26 of the climate models used by the Intergovernmental Panel on Climate Change. Every model agreed that sulfate aerosol pollution in the Northern Hemisphere triggered the terrible Sahel drought.
"Precipitation is tough to forecast, and you don't often see all the models agreeing on things like that," Frierson said. "I think it's pretty clear that in addition to greenhouse gases, air pollution really does affect climate, and not just in one place. These emissions over the U.S. and in Europe affected rainfall over Africa," he told LiveScience.
Frierson said cooling in the Northern Hemisphere sent the tropical rainfall band southward until clean air legislation significantly lessened aerosol pollution emitted in North America and Europe. Since the 1990s, tropical rainfall has drifted back toward the north, he said.
The researchers are now studying the global effects of aerosol pollution emitted in Asia.
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