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by David Pimentel, Xuewen Huang, Ana Cordova, and Marcia Pimentel

Presented at AAAS Annual Meeting, Baltimore, MD, 9 February 1996
Submitted for publication to Population and Development Review, New York, NY, USA

As the world population continues to grow geometrically, great pressure is being placed on arable land, water, energy, and biological resources to provide an adequate supply of food while maintaining the integrity of our ecosystem. According to the World Bank and the United Nations, from 1 to 2 billion humans are now malnourished, indicating a combination of insufficient food, low incomes, and inadequate distribution of food. This is the largest number of hungry humans ever recorded in history. In China about 80 million are now malnourished and hungry. Based on current rates of increase, the world population is projected to double from roughly 6 billion to more than 12 billion in less than 50 years (Pimentel et al., 1994). As the world population expands, the food problem will become increasingly severe, conceivably with the numbers of malnourished reaching 3 billion.

Based on their evaluations of available natural resources, scientists of the Royal Society and the U.S. National Academy of Sciences have issued a joint statement reinforcing the concern about the growing imbalance between the world's population and the resources that support human lives (RS and NAS, 1992).

Reports from the Food and Agricultural Organization of the United Nations, numerous other international organizations, and scientific research also confirm the existence of this serious food problem. For example, the per capita availability of world grains, which make up 80 per cent of the world's food, has been declining for the past 15 years (Kendall and Pimentel, 1994). Certainly with a quarter million people being added to the world population each day, the need for grains and all other food will reach unprecedented levels.

More than 99 per cent of the world's food supply comes from the land, while less than 1 per cent is from oceans and other aquatic habitats (Pimentel et al., 1994). The continued production of an adequate food supply is directly dependent on ample fertile land, fresh water, energy, plus the maintenance of biodiversity. As the human population grows, the requirements for these resources also grow. Even if these resources are never depleted, on a per capita basis they will decline significantly because they must be divided among more people.

At present, fertile cropland, is being lost at an alarming rate. For instance, nearly one-third of the world's cropland (1.5 billion hectares) has been abandoned during the past 40 years because erosion has made it unproductive (Pimentel et al., 1995). Solving erosion losses is a long-term problem: it takes 500 years to form 25 mm of soil under agricultural conditions.

Most replacement of eroded agricultural land is now coming from marginal and forest land. The pressure for agricultural land accounts for 60 to 80 percent of the world's deforestation. Despite such land replacement strategies, world cropland per capita has been declining and is now only 0.27 ha per capita; in China only 0.08 ha now is available. This is only 15 per cent of the 0.5 ha per capita considered minimal for a diverse diet similar to that of the U.S. and Europe. The shortage of productive cropland combined with decreasing land productivity is, in part, the cause of current food shortages and associated human malnutrition. Other factors such as political unrest, economic insecurity, and unequal food distribution patterns also contribute to food shortages.

Water is critical for all crops which require and transpire massive amounts of water during the growing season. For example, a hectare of corn will transpire more than 5 million liters of water during one growing season. This means that more than 8 million liters of water per hectare must reach the crop. In total, agricultural production consumes more fresh water than any other human activity. Specifically, about 87 per cent of the world's fresh water is consumed or used up by agriculture and, thus, is not recoverable (Pimentel et al., 1996).

Competition for water resources among individuals, regions, and countries and associated human activities is already occurring with the current world population. About 40 percent of the world's people live in regions that directly compete for shared water resources. In China where more than 300 cities already are short of water, these shortages are intensifying. Worldwide, water shortages are reflected in the per capita decline in irrigation used for food production in all regions of the world during the past twenty years. Water resources, critical for irrigation, are under great stress as populous cities, states, and countries require and withdraw more water from rivers, lakes, and aquifers every year. A major threat to maintaining future water supplies is the continuing over-draft of surface and ground water resources.

Diseases associated with water rob people of health, nutrients, and livelihood. This problem is most serious in developing countries. For example, about 90 per cent of the diseases occurring in developing countries result from a lack of clean water (Pimentel et al., 1996). Worldwide, about 4 billion cases of disease are contracted from water and approximately 6 million deaths are caused by water-borne disease each year. When a person is ill with diarrhea, malaria, or other serious disease, anywhere from 5 to 20 percent of an individual's food intake offsets the stress of the disease.

Disease and malnutrition problems in the third world appear to be as serious in rural areas as they are in urban areas, especially among the poor. This will intensify in the future. Furthermore, the number of people living in urban areas is doubling every 10 to 20 years, creating major environmental problems, including water and air pollution and increased disease and food shortages.

Fossil energy is another prime resource used for food production. Nearly 80 per cent of the world's fossil energy used each year is used by the developed countries, and part of it is expended in producing high animal protein diets. The intensive farming technologies of developed countries use massive amounts of fossil energy for fertilizers, pesticides, irrigation, and for machines as a substitute for human labor. In developing countries, fossil energy has been used primarily for fertilizers and irrigation to help maintain yields rather than to reduce human labor inputs (Giampietro and Pimentel, 1993).

Because fossil energy is a finite resource, its depletion accelerates as population needs for food and services escalate. The U.S. is already importing more than 50 per cent of its oil, and projections from the U.S. Department of Energy indicate that the country will exhaust all of its oil reserves within the next 15 to 20 years (Pimentel et al., 1994). Oil imports will then have to increase, worsening the U.S. trade imbalance. As supplies of fossil energy dwindle, the cost of fuel increases everywhere. The impact of this is already a serious problem for developing countries where the high price of imported fossil fuel makes it difficult, if not impossible, for poor farmers to power irrigation and provide for their other agricultural needs. Worldwide, per capita supplies of fossil energy show a significant decline.

In general, developing countries have been relying heavily on fossil energy, especially for fertilizers and irrigation to augment their food supply. The current decline in per capita use of fossil energy, caused by the gradual decline in oil supplies and their relatively high prices, is generating direct competition between developed and developing countries for fossil energy resources.

Economic analyses often overlook the biological and physical constraints that exist in all food production systems. The assumption is that market mechanisms and international trade are effective insurances against future food shortages. A rich economy is expected to guarantee a food supply adequate to meet a country's demand despite existing local ecological constraints. In fact, the contrary is true. When global biological and physical limits to domestic food production are reached, food importation will no longer be a viable option for any country. At that point, food importation for the rich can only be sustained by starvation of the powerless poor.

These concerns about the future are supported by two observations. First, most of the 183 nations of the world are now, to some extent, dependent on food imports. Most of these imports are cereal surpluses produced only in those countries that have relatively low population densities and practice intensive agriculture. For instance, the United States, Canada, Australia, Oceania, and Argentina provide 81 percent of net cereal exports on the world market. If, as projected, the U.S. population doubles in the next 60 years (Pimentel et al., 1994), then its cereal and other food resources would have to be used domestically to feed 520 million hungry Americans. Then the U.S. would cease to be a food exporting country.

In the future, when exporting nations must keep surpluses at home, Egypt, Jordan, and countless other countries in Africa and Asia will be without the food imports that now help them survive. China, which now imports many tons of food, illustrates this problem. As the Worldwatch Institute has pointed out, if China's population increases by 500 million and their soil erosion continues unabated, it will need to import 200-400 million tons of food each year by 2050 (Brown, 1995). But by then, sufficient food imports probably will not be available on the international market.

Certainly improved technology will assist in more effective management and use of resources, but it cannot produce an unlimited flow of those vital natural resources that are the raw materials for sustained agricultural production. For instance, fertilizers enhance the fertility of eroded soils, but humans cannot make topsoil. Indeed, fertilizers made from finite fossil fuels are presently being used to compensate for eroded topsoil. Per capita fish catch has not increased even though the size and speed of fishing vessels has improved. On the contrary, per capita fish production is lower than ever before because greater efficiency led to overfishing. In regions like eastern Canada, overfishing has been so severe that cod fishermen have no fish to catch, and the economy of that region has been devastated. All of the world's fishing grounds are facing overfishing problems.

Consider also the supplies of fresh water that are available not only for agriculture but also for industry and public use. Water withdrawn from the Colorado River in several states for irrigation and other purposes results in the river being nearly dry by the time it reaches the Sea of Cortes, Mexico. No available technology can double the flow of the Colorado River, although effective water conservation would be a help. Similarly, the shrinking ground water resources stored in vast aquifers cannot be refilled by human technology. Rainfall is the only supplier.

A productive and sustainable agricultural system depends on maintaining the integrity of biodiversity. Often small in size, diverse species are natural enemies of pests, degrade wastes, form soil, fix nitrogen, pollinate crops, etc. For example, in New York State on one bright, sunny day in July, the wild and other bees pollinate an estimated 6,000,000 million blossoms of essential fruits and vegetables. Humans have no technology to substitute for many of the services provided by diverse species in our environment.

Strategies for the future must be based first and foremost on the conservation and careful management of land, water, energy, and biological resources needed for food production. Our stewardship of world resources must change and the basic needs of people must be balanced with those resources that sustain human life. The conservation of these resources will require coordinated efforts and incentives from individuals and countries. Once these finite resources are exhausted they cannot be replaced by human technology. Further, more efficient and environmentally sound agricultural technologies must be developed and put into practice to support the continued productivity of agriculture.

Yet none of these measures will be sufficient to ensure adequate food supplies for future generations unless the growth in the human population is simultaneously curtailed. Several studies have confirmed that to maintain a relatively high standard of living, the optimum population should be less than 200 million for the U.S. and less than 2 billion for the world (Pimentel et al., 1994). This assumes that from now until an optimum population is achieved, strategies for the conservation of land, water, energy, and biological resources are successfully implemented and a sound, productive environment is protected.



Brown, L.R. 1995. Who Will Feed China? New York: W.W. Norton.

Giampietro, M., and D. Pimentel. 1993. The Tightening Conflict: Population, Energy Use, and the Ecology of Agriculture. Edited by L. Grant. Negative Population Forum. Teaneck, NJ: Negative Population Growth, Inc.

Kendall, H.W., and D. Pimentel. 1994. "Constraints on the expansion of the global food supply." Ambio 23: 198-205.

Pimentel, D., R. Harman, M. Pacenza, J. Pecarsky, and M. Pimentel. 1994. "Natural resources and an optimum human population." Population and Environment 15 : 347-369.

Pimentel, D., C. Harvey, P. Resosudarmo, K. Sinclair, D. Kurz, M. McNair, S. Crist, L. Sphpritz, L. Fitton, R. Saffouri, and R. Blair. 1995. "Environmental and economic costs of soil erosion and conservation benefits." Science 267 : 1117-1123.

Pimentel, D., J. Houser, E. Preiss, O. White, H. Fang, L. Mesnick, T. Barsky, S. Tariche, J. Schreck, and S. Alpert. 1996. "Water resources: agriculture, the environment, and society." BioScience (in press).

RS and NAS. 1992. "The Royal Society and the National Academy of Sciences on Population Growth and Sustainability." Population and Development Review 18 (2) : 375-378.

David Pimentel, College of Agriculture and Life Sciences
Xuewen Huang, College of Agriculture and Life Sciences
Ana Cordova, College of Agriculture and Life Sciences
Marcia Pimentel, Division of Nutritional Sciences
5126 Comstock Hall
Cornell University, Ithaca, NY 14853-0901

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