EPIBuilding a Sustainable Future
Lester R. Brown

Chapter 1. A Planet under Stress: Farmers Facing Two New Challenges

As we exceed the earth's natural capacities, we create new problems. For example, farmers are now facing two new challenges: rising temperatures and falling water tables. Farmers currently on the land may face higher temperatures than any generation since agriculture began 11,000 years ago. They are also the first to face widespread aquifer depletion and the resulting loss of irrigation water.

The global average temperature has risen in each of the last three decades. The 16 warmest years since recordkeeping began in 1880 have all occurred since 1980. With the three warmest years on record1998, 2001, and 2002—coming in the last five years, crops are facing heat stresses that are without precedent.16

Higher temperatures reduce crop yields through their effect on photosynthesis, moisture balance, and fertilization. As the temperature rises above 34 degrees Celsius (94 degrees Fahrenheit), photosynthesis slows, dropping to zero for many crops when it reaches 37 degrees Celsius (100 degrees Fahrenheit). When temperatures in the U.S. Corn Belt are 37 degrees or higher, corn plants suffer from thermal shock and dehydration. They are in effect on sick leave. Each such day shrinks the harvest.17

In addition to decreasing photosynthesis and dehydrating plants, high temperatures also impede the fertilization needed for seed formation. Researchers at the International Rice Research Institute in the Philippines and at the U.S. Department of Agriculture have together developed a rule of thumb that each 1-degree-Celsius rise in temperature above the optimum during the growing season reduces grain yields by 10 percent.18

These recent research findings indicate that if the temperature rises to the lower end of the range projected by the Intergovernmental Panel on Climate Change, grain harvests in tropical regions could be reduced by an average of 5 percent by 2020 and 11 percent by 2050. At the upper end of the range, harvests could drop 11 percent by 2020 and 46 percent by 2050. Avoiding these declines will be difficult unless scientists can develop crop strains that are not vulnerable to thermal stress.19

The second challenge facing farmers, falling water tables, is also recent. With traditional animal- or human-powered water-lifting devices it was almost impossible historically to deplete aquifers. With the worldwide spread of powerful diesel and electric pumps during the last half-century, however, overpumping has become commonplace.

As the world demand for water has climbed, water tables have fallen in scores of countries, including China, India, and the United States, which together produce nearly half of the world's grain. Water tables are falling throughout the northern half of China. As the water table falls, springs and rivers go dry, lakes disappear, and wells dry up. Northern China is literally drying out. Water tables under the North China Plain, which accounts for a fourth or more of China's grain harvest, are falling at an accelerating rate.20

In India, water tables are also falling. As India's farmers try to feed an additional 16 million people each year, nearly the population equivalent of another Australia, they are pumping more and more water. This is dropping water tables in states that together contain a majority of India's 1 billion people.21

In the United States, the third major grain producer, water tables are falling under the southern Great Plains and in California, the country's fruit and vegetable basket. As California's population expands from 34 million to a projected 45 million by 2030, expanding urban water demands will siphon water from agriculture.22

Scores of other countries are also overpumping their aquifers, setting the stage for dramatic future cutbacks in water supplies. The more populous among these are

Pakistan, Iran, and Mexico. Overpumping creates an illusion of food security that is dangerously deceptive because it enables farmers to support a growing population with a practice that virtually ensures a future drop in food production.

The water demand growth curve over the last half-century looks like the population growth curve, except that it climbs more steeply. While world population growth was doubling, the use of water was tripling. Once the growing demand for water rises above the sustainable yield of an aquifer, the gap between the two widens further each year. As this happens, the water table starts to fall. The first year after the sustainable yield is surpassed, the water table falls very little, with the drop often being scarcely perceptible. Each year thereafter, however, the annual drop is larger than the year before.

In addition to falling exponentially, water tables are also falling simultaneously in many countries. This means that cutbacks in grain harvests will occur in many countries at more or less the same time. And they will occur at a time when the world's population is growing by more than 70 million a year.23

These, then, are the two new challenges facing the world's farmers: rising temperatures and falling water tables. Either one by itself could make it difficult to keep up with the growth in demand. The two together provide an early test of whether our modern civilization can cope with the forces that threaten to undermine it.


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16. Goddard Institute for Space Studies, NASA Goddard Space Flight Center Earth Sciences Directorate, "Global Temperature Anomalies in .01 C," at www.giss.nasa.gov/data/update/gistemp/GLB.Ts.txt, viewed 15 April 2003.

17. Effect of higher temperatures from John E. Sheehy, International Rice Research Institute, Philippines, e-mail to Janet Larsen, Earth Policy Institute, 2 October 2002.

18. Ibid.

19. U. Cubasch et al., "Projections of Future Climate Change," in Intergovernmental Panel on Climate Change, Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change (New York: Cambridge University Press, 2001).

20. Grain from USDA, op. cit. note 8; World Bank, China: Agenda for Water Sector Strategy for North China (Washington, DC: April 2001), pp. vii, xi; water tables falling from Sandra Postel, Last Oasis (New York: W.W. Norton & Company, 1997), pp. 36-37.

21. United Nations, op. cit. note 3; Postel, op. cit. note 20.

22. USDA, op. cit. note 5; U.S. Bureau of the Census, Projections of the Total Population of States: 1995-2025, at www.census.gov, updated 2 August 2002.

23. David Seckler, David Molden, and Randolph Barker, "Water Scarcity in the Twenty-First Century," Water Brief 1 (Colombo, Sri Lanka: International Water Management Institute, 1999); population from United Nations, op. cit. note 3.


Copyright © 2003 Earth Policy Institute