Plants may seem to sit passively as climate decides their fate, but scientists are beginning to believe that vegetation can strongly amplify the climate's most subtle whims--sometimes with abrupt and devastating results. A new computer simulation indicates that plants helped to turn the Sahara from a lush grassland thriving with hippos and elephants to its current condition as the world's largest desert.
The Sahara's succulent sojourn faced an abrupt end about 5,500 years ago. In a matter of centuries, rainfall levels plummeted, the green grasslands paled to a sandy yellow, and civilizations were forced to relocate. Many scientists have assumed that human beings, who arrived there 7,000 years ago, overused the land, which led to the quick loss in vegetation. But the new simulations show that a steady but slow loss of grasses--stemming from a gradual trend toward less rainfall beginning about 9,000 years ago--ran wildly out of control.