Population Growth, Environmental Resources, and the Global Availability of Food

Social Research, Spring, 1999 by David Pimentel, Marcia Pimentel

Agricultural shortages exist because the human population is increasing faster than the food production capability of the agricultural system. Uneven distribution of food, inability to afford food, and political unrest also threaten world food security for human society.

Currently, more than three billion humans worldwide are malnourished; this is the largest number and proportion of hungry people ever recorded in history (WHO, 1996)! Based on current rates of increase, the world population is projected to double to more than 12 billion in less than 50 years (PRB, 1997). As the world population continues to expand at a rate of 1.5%/year--adding more than a quarter million people daily--the task of providing adequate food becomes an increasingly difficult problem. The number of malnourished people could conceivably reach four to five billion in future decades.

Reports from the Food and Agriculture Office (FAO) of the United Nations and the U.S. Department of Agriculture, as well as numerous other international organizations, further confirm the serious nature of the global food supply problem (NAS, 1994). For example, the per capita availability of world cereal grains, which make up 80% of the world's food supply, has been declining since 1983 (Figure 1) (Kendall and Pimentel, 1994). These shortages have economic consequences as well, as is reflected in recent major increases in the price of cereal grains (USDA, 1996).

[Figure 1 ILLUSTRATION OMITTED]

Because the world population continues to expand, more pressure than ever before is being placed on the basic resources that are essential for food production. Unfortunately, the human population is growing exponentially, whereas food production can only increase linearly. Furthermore, degradation of land, water, energy, and biological resources that are vital to a sustainable agriculture continues unabated (Pimentel et al., 1998a).

Agricultural Resources

More than 99% of the world's food supply comes from the land; less than 1% is obtained from oceans and other aquatic habitats (FAO, 1991; Pimentel et al., 1998a). As mentioned previously, the continued production of an adequate food supply is directly dependent on the availability of ample quantities of fertile land, fresh water, energy, and natural biodiversity. And obviously, as the human population grows, the requirements for all these resources escalates. Even if these resources are never completely depleted, their supply, on a per capita basis, will decline significantly because they must be divided among more and more people.

Land

Throughout the world, fertile cropland is being lost from production at an alarming rate. This is clearly illustrated by the diminishing amount of land now devoted to cereal grains (Figure 2). Soil erosion by wind and water, in addition to general overuse of the land, are responsible for the loss of about 30% of the world's cropland during the past 40 years (WRI, 1994; Pimentel et al., 1995). The natural reformation of a mere 25 mm (1 inch) of fertile soil takes 500 years; to sustain adequate crop production, a soil depth of 150 mm is needed.

[Figure 2 ILLUSTRATION OMITTED]

Most eroded and unproductive agricultural land is now being replaced with cleared forest land and/or marginal land. Indeed, the urgent need for more cropland accounts for more than 60% of the world's deforestation (Myers, 1994). Despite such land replacement strategies, per capita world cropland is declining, currently standing at only 0.27 ha per capita. This is only about 50% of the 0.5 ha per capita that is considered the minimum land area needed for the production of a diverse diet similar to that of the United States and Europe (Lal and Stewart, 1990; Pimentel et al., 1998a). Other countries have even less land; for example, China now has only 0.08 ha available per capita, about 15% of the accepted minimum (Pimentel et al., 1998a).

Water

Rainfall, and its collection in rivers, lakes, and vast underground aquifers, provides the water needed by humans for their personal survival and diverse activities.

Fresh water is critical for all vegetation, especially crops. All plants transpire massive amounts of water during the growing season. For example, a hectare of corn, producing about 8,000 kg, transpires more than five million liters of water during just one growing season (Pimentel et al., 1997a). This means that more than eight million liters of water must reach each hectare during the growing season both as rainfall and irrigation, to provide the adequate water supply for crop production. In total, agricultural production consumes more fresh water than any other human activity. About 70% of the world's fresh water supply is consumed, or used up by agriculture, making it unavailable for other uses (Postel, 1996).

Water resources are continually stressed as populous cities, states, and countries increase their withdrawal of water from rivers, lakes, and aquifers every year. For example, by the time the Colorado River reaches Mexico it has dwindled down to a trickle (Sheridan, 1983; Postel, 1996). Also, the great Ogalla aquifer in the central U.S. is suffering an overdraft rate that is about 140% above its natural recharge rate (Gleick, 1993). Water shortages in the U.S. and elsewhere in the world are already reflected in the per capita decline in crop irrigation that has occurred during the past twenty years (Postel, 1996).