In some parts of the world, the historic trend toward longer life has been abruptly reversed. Even as world population continues to climb, it is becoming clear that the several billion additional people projected for the next half century are not likely to materialize. What is not clear is how the growth will be curtailed. They argue that without clearly defined national strategies for quickly lowering birth rates in certain countries, and without a commitment by the international community to support these efforts, one-third of humanity could slide into a demographic black hole. During the last three decades, the depletion of underground water reserves, known as aquifers, has spread from isolated pockets of the agricultural landscape to large portions of the world's irrigated land.
Irrigated land is disproportionately important to world food production.
Some 40 percent of the global harvest comes from the 17 percent of cropland that is irrigated. The world is betting on that share to increase markedly in the decades ahead, in order to feed the world's growing population. Postel reviews how groundwater overpumping may now be the single biggest threat to food production. See a related news release on drought and information on Postel's new book Pillar of Sand .