The renowned physicist muses on the days when the Sahara was wet.

Randall Hagadorn, Courtesy of the Institute for Advanced Study

The mystery of the wet Sahara has fascinated me ever since I read Henri Lhote’s book, The Search for the Tassili Frescoes, first published in English in 1959. The book includes reproductions of 50 rock paintings, showing people with herds of animals. The paintings are abundant and of superb artistic quality, comparable with the famous cave paintings at sites in France and Spain.

The Saharan rock paintings are actually more recent than the cave paintings; they were probably painted over a period of several thousand years, up until roughly 5,000 years ago. They are strong evidence that the Sahara was wet at that time. There appears to have been enough rain to support herds of cows and giraffes, which must have grazed on grass and trees. There were also some hippopotamuses and elephants, suggesting that the Sahara must have been like the Serengeti today.

At roughly the same point in the earth’s history, there were also trees standing in mountain valleys in Switzerland, valleys that are now filled with famous glaciers; these glaciers, which are shrinking, were smaller then than now. Six thousand years ago seems to have been the warmest and wettest period of the interglacial era, which began 12,000 years ago (when the last ice age ended).

Given the current warming trend, I would like to ask the following two questions: First, if the modern increase of carbon dioxide in the atmosphere continues, shall we arrive at a climate similar to the climate of 6,000 years ago, when the Sahara was wet? Second, if we could choose between the climate of today with a dry Sahara and the climate of 6,000 years ago with a wet Sahara, should we prefer the climate of today? Since I am a heretic, I am inclined to answer yes to the first question and no to the second.

Freeman Dyson is a futurist and professor emeritus of physics at the Institute for Advanced Study in Princeton, New Jersey.

Originally published March 22, 2006


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