The combined effect of these three growing demands is stunning: a doubling in the annual growth in world grain consumption from an average of 21 million tons per year in 1990-2005 to 41 million tons per year in 2005-2010. Most of this huge jump is attributable to the orgy of investment in ethanol distilleries in the United States in 2006-2008.
While the annual demand growth for grain was doubling, new constraints were emerging on the supply side, even as longstanding ones such as soil erosion intensified. An estimated one third of the world's cropland is losing topsoil faster than new soil is forming through natural processes -- and thus is losing its inherent productivity. Two huge dust bowls are forming, one across northwest China, western Mongolia, and central Asia; the other in central Africa. Each of these dwarfs the U.S. dust bowl of the 1930s.
Satellite images show a steady flow of dust storms leaving these regions, each one typically carrying millions of tons of precious topsoil. In North China, some 24,000 rural villages have been abandoned or partly depopulated as grasslands have been destroyed by overgrazing and as croplands have been inundated by migrating sand dunes.
In countries with severe soil erosion, such as Mongolia and Lesotho, grain harvests are shrinking as erosion lowers yields and eventually leads to cropland abandonment. The result is spreading hunger and growing dependence on imports. Haiti and North Korea, two countries with severely eroded soils, are chronically dependent on food aid from abroad.
Meanwhile aquifer depletion is fast shrinking the amount of irrigated area in many parts of the world; this relatively recent phenomenon is driven by the large-scale use of mechanical pumps to exploit underground water. Today, half the world's people live in countries where water tables are falling as overpumping depletes aquifers. Once an aquifer is depleted, pumping is necessarily reduced to the rate of recharge unless it is a fossil (nonreplenishable) aquifer, in which case pumping ends altogether. But sooner or later, falling water tables translate into rising food prices.