Dr. Stefan Kroepelin, a geologist and climate researcher at the University of Cologne, studies the 10,000-year interplay of human settlements and the Sahara’s changing climate.

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Egypt’s pharaonic civilization rose on the Nile, but it was rooted in the deep Saharan desert and pushed by climate change, says Stefan Kröpelin.

Described in Nature magazine as “one of the most devoted Sahara explorers of our time,” Kröpelin has survived every kind of desert hardship to discover the climate and cultural history of northern Africa. He found that the “Green Sahara” arrived with monsoon rains 10,500 years ago, and people quickly moved into the new fertile savannah. There they prospered as cattle pastoralists—their elaborate rock paintings show herds of rhinoceros and scenes of prehistoric life—until 7,300 years ago, when gradually increasing desiccation drove them to the Nile river, which they had previously considered too dangerous for occupation.

To manage the Nile, the former pastoralists helped to invent a pharaonic state 5,100 years ago. Its 3,000-year continuity has never been surpassed.

Kröpelin, a climate scientist at the University of Cologne, is a dazzling speaker with hair-raising stories, great images, and a compelling tale about climate change and civilization.

The Sahara and civilization

“Almost everything breaks in the desert,” Kröpelin began. He showed trucks mired in sand, one vehicle blown up by a land mine, and a Unimog with an impossibly, hopelessly broken axle. (Using the attached backhoe, it hunched its way 50 miles back to civilization.)

The eastern Sahara remains one of the least explored places on Earth, and it is full of wonders. Every year for 40 years Kröpelin has made multi-month expeditions to figure out the paleoclimatological changes and human saga in the region over the last 17,000 years. There are no guides, no roads. When you find something—astonishing rock art (there are thousands of sites), an amazing geological feature—you know you’re the first human to see it in thousands of years.

A great river, 7 miles wide, 650 miles long, once flowed into the Nile from the desert. Now called Wadi Howar, its rich, still unstudied archeological sites show it used to be a thoroughfare from the deep desert. A vast spectacular plateau called the Ennedi Highlands, as big as Switzerland, has exquisite rock art detailing pastoral herds of cattle and even dress and hair styles. Mouflon (wild sheep) and crocodiles still survive there.

Most remarkable of all are the remote Ounianga Lakes, some of them kept charged with ancient deep-aquifer fresh water because of the draw of intense evaporation from a hypersaline central lake. In 1999 Kröpelin began a stratigraphic study of another lake’s sediment, eventually collecting a treasure for climate study---a 52-foot core sample which shows every season for the last 11,000 years.

For Kröpelin, many strands of evidence spell out the sequence of events in the eastern Sahara. From 17,000 to 10,500 BP (before the present), there were only a few human settlements along the Nile. But the Sahara was gradually getting wetter in the period 10,500 to 9,000 BP, and people moved up from the south. The peak of the African Humid Period, when the Sahara was green and widely occupied, was 9,000 to 7,300 years ago. Then a gradual desiccation from 7,300 to 5,500 BP drove people to the Nile, and the first farms appeared there. From 5,500 BP on, the Nile’s pharaonic civilization got going and lasted 3,000 years.

Unique artifacts such black-rimmed pots and asymmetric stone knives, once used in the far desert, turn up in the settlements that created Egypt. Kröpelin concluded: “Egypt was a gift of the Nile, but it was also a gift of the desert.”

And of climate change.