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The devastating drought that hit Africa's Sahel region in the 1970s and 1980s was caused by warming of the Indian Ocean, and not environmental degradation by humans as previously thought, according to a new study.

Alessandra Giannini of the US National Center for Atmospheric Research in Boulder, Colorado, and colleagues used a climate model to explore the effects of sea surface temperatures from 1930 to 2000. They report in this week's Science Express that their model could reproduce the Sahel's rainfall record over the same time period.

Many researchers have suggested that the drought in this semiarid region in West Africa was largely due to human land use. According to one hypothesis, the expansion of farming and herding into marginal areas produced a spiral of changes, in which reduced vegetation led to reduced rainfall, producing further decreases in vegetation and still less rainfall.

But even if warming of the Indian Ocean caused the drought, humans might still be to blame. "People have put out the idea that it could be global warming, but it's not at all tested," Giannini told Science.

Link to news story in Science: 'Warming Indian Ocean wringing moisture from the Sahel'

Link to research paper in Science Express by A. Giannini et al

References: Science 302, 210 (2003)/ Science Express 9 October 2003