vinces99 writes "Decades of drought in central Africa reached their worst point in the 1980s, causing Lake Chad, a shallow lake used to water crops in neighboring countries, to almost dry out completely. The shrinking lake and prolonged drought were initially blamed on overgrazing and bad agricultural practices. More recently, Lake Chad became an example of global warming. But new University of Washington research shows the drought was caused at least in part by Northern Hemisphere air pollution. Particles 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. That meant that rains no longer reached the Sahel region, a band that spans the African continent just below the Sahara desert."