Science Daily: A new study of lake sediments in Ghana suggests that severe droughts lasting several decades, even centuries, were the norm in West Africa over the past 3,000 years. The earlier dry spells dwarfed the well-documented drought that plagued West Africa in the late-20th century, and as the planet warms, the study's authors believe the region's rainfall patterns will have an even greater impact.The team of geoscientists and climate scientists, led by Jonathan Overpeck of the University of Arizona and his former doctoral student, lead author Timothy Shanahan, who is now at the University of Texas (UT) at Austin, announced their findings in the April 17, 2009, issue of Science.
Because of close agreement amongst several data sets, the scientists believe the droughts are driven in part by circulation of the ocean and atmosphere in and above the Atlantic--and possibly beyond. If climate models for such circulation patterns hold true, the study suggests global warming could create conditions that favor extreme droughts. "Clearly, much of West Africa is already on the edge of sustainability," says Overpeck, "and the situation could become much more dire in the future with increased global warming."
The findings emerged from sediments that lie at the bottom of Lake Bosumtwi in Ghana, deposits of soil and organic matter that contain annual bands of light (winter) and dark (summer) layers that stretch back more than three millennia. "Lake Bosumtwi is really unique in that its one of the few locations in tropical West Africa where varves, annual sediment layers, are preserved. This allows us to look at changes in climate at very high resolution," said Shanahan, now an assistant professor at UT….
Lake Bosumtwi in Ghana, shot by Stig Nygaard from Copenhagen, Denmark, Wikimedia Commons via Flickr, under Creative Commons Attribution 2.0 License
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