A team of US geoscientists and climate scientists found that severe droughts lasting several decades and sometimes even centuries have been the norm in west Africa for the past three centuries.
The most recent such drought lasted from 1400 to 1750, according to the researchers, whose study was published in the journal Science.
It was the first study to examine climate conditions in west Africa over thousands of years by analysing annual layers of mud and tree sediment in Ghana's Lake Bosumtwi, a crater lake.
'Clearly, much of west Africa is already on the edge of sustainability,' said University of Arizona geoscience professor Jonathan Overpeck, the study's lead author, 'and the situation could become much more dire in the future with increased global warming.'
The latest Sahel drought killed over 100,000 people and displaced scores more, according to a 2002 report by the United Nations Environment Program.