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Chapter 2. Population Pressure: Land and Water: Introduction
The French use a riddle to teach schoolchildren the nature of exponential growth. A lily pond, so the riddle goes, contains a single leaf. Each day the number of leaves doubles—two leaves the second day, four the third, eight the fourth, and so on. “If the pond is full on the thirtieth day, at what point is it half full?” Answer: “On the twenty-ninth day.” 1
Trends in world cropland area and irrigation water supplies suggest that we are living in the thirty-first day. After expanding modestly from 1950 to 1981, world grain area stopped growing and the area declined somewhat as land losses from erosion and conversion to nonfarm uses offset new land brought under the plow. On close to one third of the world’s cropland, topsoil is eroding faster than new soil is being formed by geological processes, slowly reducing the land’s inherent productivity. 2
The world’s irrigated area tripled from 1950 to 2000 but has expanded little since then. It could soon begin to decline—as it is already doing in some countries—as aquifers are depleted by overpumping and as the mountain glaciers that sustain so many of the world’s rivers and irrigation systems melt and disappear. Many irrigation systems, whether dependent on underground water or on river water, are at risk. 3
We cannot escape the water intensity of food production. Worldwide, we drink on average close to 4 liters of water per day, either directly or in coffee, juice, soda, wine, and other beverages. But it takes 2,000 liters of water to produce the food we consume each day—500 times as much as we drink. In effect, we “eat” 2,000 liters of water each day. 4
Soil erosion initially reduces the inherent productivity of the land and then, after a point, leads to cropland abandonment. Both effects of erosion are undermining world food security. A combination of population growth and soil erosion has caused a number of countries that were once self-sufficient in grain to become heavily dependent on imports.
With water tables now falling in almost every country that irrigates with underground water, many of these countries are facing hunger-inducing losses of irrigation water as aquifers are depleted and wells go dry. Overpumping—the pumping of aquifers that exceeds the natural recharge—presents a classic case of ecological overshoot and collapse. It is a way of satisfying current food needs that virtually guarantees a future drop in food production when aquifers are depleted. In effect, we have created a “food bubble economy.” Both soil erosion and aquifer depletion reflect an emphasis on current consumption at the expense of the next generation. 5
2. Grain area from U.S. Department of Agriculture (USDA), Production, Supply and Distribution, electronic database, at www.fas.usda
.gov/psdonline, updated 9 April 2009; cropland losing topsoil is author’s estimate based on Mohan K. Wali et al., “Assessing Terrestrial Ecosystem Sustainability,” Nature & Resources, October-December 1999, pp. 21–33, and on World Resources Institute (WRI), World Resources 2000–01 (Washington, DC: 2000).
3. U.N. Food and Agriculture Organization (FAO), ResourceSTAT, electronic database, at faostat.fao.org, updated April 2009; Lester R. Brown, “Melting Mountain Glaciers Will Shrink Grain Harvests in China and India,” Plan B Update (Washington, DC: Earth Policy Institute, 20 March 2008).
4. Jacob W. Kijne, Unlocking the Water Potential of Agriculture (Rome: FAO, 2003), p. 26.
5. Lester R. Brown, Outgrowing the Earth (New York: W. W. Norton & Company, 2004), pp. 101–02.
Copyright © 2009 Earth Policy Institute