From 1970 to 1985, a wide swath of Africa lay under the siege of a brutal drought that ultimately left 1.2 million dead. Now, a group of scientists from Australia and Canada says the deadly drought may have been caused in part by pollution from factories and power plants in North America, Europe, and Asia. In a process known as teleconnection, tiny aerosols — in this case, particles of sulfur dioxide — from those sources altered the formation of clouds and reduced rainfall in Africa by as much as 50 percent, the scientists say. Although environmental regulation of aerosols became much stricter in the 1990s, teleconnection continues today, and some suggest it might account for the drought currently gripping much of the United States. The African drought has also been attributed to other factors ranging from El Nino to overgrazing, and the authors of the current study acknowledge that teleconnection was probably just one of a combination of factors leading to the lack of rain.