China's growing deserts.

In northern and northwest China, there are 1.1 million square kilometers of desert. But only 61 percent of this represents true climatic desert, caused by less than 100 millimeters of precipitation annually. roughly 170,000 square kilometers are human-made deserts; another 260,000 are arid steppes undergoing or seriously threatened with desertification as a result of human activities, according to Bill Dahl of Texas Technological University in Lubbock. Dahl, who has toured affected areas studying the human abuse of these arid lands, says Chinese scientists now cite population pressures "as the primary cause of environmental deterioration in this area."

"Exploitative land management," he says, has produced a vicious cycle: Expanding cultivation of the steppes leads to wind erosion, which reduces soil fertility, which reduces the land's agricultural, productivity, which in the end leads to an expansion of cultivation. It's analogous, he says, to what is occurring in Africa. Dahl cites Chinese data suggesting overcultivation was responsible for 45 percent of the desertification, overgrazing for 27 percent, firewood collection for 18 percent, urbanization and roads for 3 percent and misuse of water resources for 1.5 percent. Fostering this problem, he says, is a population growth rate in northwest China, "where birth control is not enforced on the minorities," of roughly 2.8 percent--a rate about as high as anywhere in the world.