Natural Variability of the Asian, Indian and African Monsoons over the Last 130 KA

A review of the geological multi-proxy records observed over the transitional area extending, in northern Africa and Asia, between the humid tropics and the desert belts, is presented for the last 130 ka. Long-term arid/humid alternations took place in rough phase with the global cold/warm variations, reflecting a coherent behaviour of the monsoon patterns, cold phases corresponding to an extension of the arid zones to the South, warm phases corresponding to their regression to the North. The total surface affected by the induced sharp environmental changes between the last two climatic extremes was about 14 000 000 km2, which may have highly contributed to the variations of the methane atmospheric ratio.