UCL in the News: Shift From Savannah to Sahara Was Gradual

Kenneth Chang, 'New York Times'  Six thousand years ago, northern Africa was a place of trees, grasslands, lakes and people.

Today, it is the Sahara - a desolate area larger area than Australia.

Lake Yoa, in northeastern Chad, has remained a lake through the millennia and is still a lake today, surrounded by hot desert. …

By analyzing thousands of layers sediment in a core drilled from the bottom of this lake, an international team of scientists has reconstructed the region's climate as the savannah changed to Sahara. …

In Friday's issue of the journal Science, the researchers, led by Stefan Kröpelin, a geologist with the Institute of Prehistoric Archaeology at the University of Cologne in Germany, report that the climate transition occurred gradually. …

The findings run counter to a prevailing view that the change happened abruptly, within a few centuries, about 5,500 years ago. …

That view arises from ocean sediment cores drilled off the coast of Africa, to the west of Mauritania. …

"On the face of it, it's puzzling," said Jonathan A. Holmes, director of the UCL Environmental Change Research Center. Dr. Holmes said both sets of research had been carefully done, and the challenge will be to put together a more complex history of the Sahara's climate. …

Dr. Holmes said one possibility was that the offshore dust might reflect a drop in water levels around Lake Chad, revealing more dust-producing soil, rather than a large-scale change in climate. …