New research from the University of Washington shows that air pollution from the Northern Hemisphere indirectly caused reduced rainfall over Africa's largely arid Sahel region, causing Lake Chad, a major local water source, to dry up, and leading to widespread crop failures.
Originally, the drought was blamed on overgrazing and poor land management, but a forthcoming study in Geophysical Research Letters shows that the environmental catastrophe was partly the result of factory emissions in the Western world. As the University of Washington puts it:
Aerosols emanating from coal-burning factories in the United States and Europe during the 1960s, '70s and '80s cooled the entire Northern Hemisphere, shifting tropical rain bands south. Rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert.
Burning coal generates sulfate aerosols, particles that create hazy air and reflective clouds that cool the climate around them. Meanwhile, the world overall was getting warmer, thanks to rising greenhouse gas emissions, so the net temperature felt normal to Northern Hemisphere-dwellers at the time, the authors wrote.
This cooling disrupted normal rainfall: Other areas near the same latitude as North Africa, like some northern parts of India, also saw reduced precipitation during those decades. As further proof, the researchers found that the normal rain patterns were restored soon after clean-air laws were passed in Europe and the U.S.
These days, it appears the trend is being reversed: The Northern Hemisphere is warming faster than the Southern Hemisphere, a trend that's shifting tropical rainfall northward.
"To some extent, science messed this one up the first time around," the study's co-author, UW associate professor of atmospheric sciences Dargan Frierson, said. "People thought that a large part of that drought was due to bad farming practices and desertification."
While it's satisfying to have an explanation for this phenomenon (and to exculpate Sahelian farmers), in some ways the real answer is even more unsettling than the previously-held, wrong one.