If people had the means to leave, they left," says Mathieu Ouédraogo, a development specialist in Burkina Faso, a landlocked nation in the heart of the Sahel. "The only people who stayed here had nothing—not enough to leave."
Scientists still dispute why the Sahel transformed itself from a savanna into a badland. Suggested causes include random changes in sea-surface temperatures, air pollution that causes clouds to form inopportunely, removal of surface vegetation by farmers moving into the desert periphery—and, of course, global warming. Whatever the cause, the consequences are obvious: Hammered by hot days and harsh winds, much of the soil turns into a stone-hard mass that plant roots and rainwater cannot penetrate. A Sahelian farmer once let me hack at his millet field with a pick. It was like trying to chop up asphalt.