The Sahara
The Sahara is the largest hot desert on Earth, filling nearly all of northern Africa from the Atlantic coast to the Red Sea. Britannica gives it a total area of some 3,320,000 square miles (8,600,000 square km) — but the figure depends on how the desert boundary is drawn: an analysis of twentieth-century rainfall puts the climatological Sahara at 7,426,000 square km, while other reviews cite about 9.2 million square km. Some 2.5 million people live in the desert itself, in oases and along its margins — Tuareg, Teda, Chaamba and other communities whose camel caravans once linked the Mediterranean world to Timbuktu. Between about 14,800 and 5,500 years ago much of the Sahara was green, a landscape of rivers, lakes and savanna known as the African Humid Period; the rock art of Tassili n'Ajjer and the Ennedi Massif still records elephants, giraffes and hippopotamuses where there is now sand. Today the Sahara lifts some 182 million tons of dust past its western edge every year, studies indicate it expanded about 10 percent during the twentieth century, and its fossil aquifers, oil, gas and mineral wealth shape the economies of the region.