Third millennium BC climate change and old world collapse

In tropical Africa the transition from the Middle Holocene (ca. 7000 to 3800 years BP) climate to the Late Holocene (ca. 3800 BP to present) was abrupt and marked by major paleoenvironmental shifts. The sediment and lake level changes in forested equatorial belt of tropical Africa, in the Sahel and Sahara and in the tropical areas of other continents (India, Australia and South America) are interpreted in terms of paleoclimate based on comparison made between the African paleodata and some present-day rainfall anomalies. These anomalies are associated with sea surface temperature (SST) variations and are closely linked to the intensity of upwelling and trade winds. We conclude that the abrupt changes in the tropical belt at the beginning of the Late Holocene could be related to the variation of the Zonal Walker Circulation, mainly the El Nino-Southern Oscillation (ENSO). The SST opposition between northern and southern Atlantic Ocean has a major influence on climatic changes in tropical Africa. Moreover, the predicted global warming during the next century could lead in tropical Africa to climate induced large rain forest destructions. (Résumé d'auteur