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Long-term climatic variations over the past 400,000 years, disclose a cyclical alternation of cold or glacial phases. At the present time, the world is experiencing one of its warmer climatic periods. Nevertheless, summer insolation has decreased sharply during the last 9,000 years and, apart from human influences, a gradual reduction in temperature, might well be expected to occur during the next 50,000’ years. On the other hand, if die human-induced ’greenhouse effect’ manifests itself as is sometimes forecast, climatic changes will take place. much faster, and temperatures could reach higher levels than in any of the post-Pleistocene interglacial phases. The future of the Sahara depends to a considerable extent upon which of these trends actually manifests itself