Scientists in Australia and Canada say that pollution from western countries may have caused the droughts which ravaged Africa's Sahel region in the 1970s and 1980s. Other Sahelian countries, from Senegal in the west stretching east to the Red Sea, were also devastated by the lack of rain and the southwards spread of the Sahara desert. The research says that sulphur dioxide from factories in Europe and the United States has cooled the Northern Hemisphere, driving the tropical rain belt south away from the Sahel.