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Holocene climate change in the Eastern Sahara: Lessons from the past

Dr Stefan Kröpelin | Institute of Prehistoric Archaeology | University of Cologne

Abstract: A summary of geological and archaeological research undertaken during the last 40 years in the Eastern Sahara of Libya, Egypt, Chad and Sudan – presently the largest hyperarid hot desert on Earth – suggests a consistent model of climate change and prehistoric migration for a coherent region of sub-continental scale throughout the Holocene. Key archives are lacustrine deposits, botanical and faunal remains, and the distribution of ancient settlements. Humans in drylands are sensitive indicators of environmental change. Their archaeological record, or its absence, traces variations in rainfall and living conditions and reveals a nearly latitudinal shift of the desert margins from the dawn of the so-called “Green Sahara” until recent times.
Main results prove the early Holocene regreening and reoccupation of the Eastern Sahara at 8500 BCE, ending the apparently continuous late Pleistocene hyperaridity since the Eemian interglacial over 100,000 years ago, and allow the identification of climatic zones and climate-controlled cultural and socioeconomic responses during the following humid optimum. The gradual drying of the Sahara started at the tropic of Cancer around 5300 BCE and lasted about 5000 years. The desiccation of one third of the African continent was linked to important developments in the history of civilization and can be considered a motor of Africa’s evolution.
The multiproxy terrestrial data set contradicts the concept of the so-called “African Humid Period” that has been deduced from a single ocean core alone, and discloses agreements and discrepancies to ice core data and numeric climate models. As a distinct natural analogue, it helps to foresee how North Africa’s climate and environments might evolve due to anthropogenic global warming.
Increasing precipitation in uninhabited regions of the southern Sahara since the late 1980s may be a first effect of global warming, and explained by higher evaporation over the heating oceans and intensifying monsoons which bring more moisture into the northern hemisphere deserts, just like after the last Ice Age. Disputing the generally postulated desert encroachment, a continuation of this trend would be a blessing signal for the Sahelian belt, and counteract man-made desertification by exponentially increasing populations.