The largest desert of all, the Sahara in North Africa, contains half the desert surface of the world​—three and a half million square miles of it.a

“In One Year, Sahara Engulfs Much of Chad,” heralds another. Reams are being written on the threat of spreading deserts.

Now read below the headlines. “The Sahara has been extending its desert barrenness southward at the rate of 6 to 12 miles [10 to 20 km] a year for more than a decade, gradually incorporating the Sahel, the semiarid belt at its southern fringe,” says The New York Times of January 2, 1985.