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'WILL LIMITS OF THE EARTH’S RESOURCESCONTROL HUMAN NUMBERS?
by David Pimentel, O. Bailey, P. Kim,E. Mullaney, J. Calabrese, L. Walman,F. Nelson, and X. Yao.

College of Agriculture and Life SciencesCORNELL UNIVERSITYIthaca, NY 14853-0901February 25, 1999

Introduction
The current world population is about 6 billion. Based on the present growth rate of 1.5% per year, the population is projected to double in approximately 46 years (PRB, 1996). Because population growth can not continue indefinitely, society can either voluntarily control its numbers or let natural forces such as disease, malnutrition, and other disasters limit human numbers (Pimentel et al., 1994a; Bartlett, 1997-98). Increasing human numbers, especially in urban areas, and increasing food, water, air, and soil pollution by pathogenic organisms and chemicals, are causing a rapid increase in the prevalence of disease and number of human deaths (WHO, 1992, 1995; Murray and Lopez, 1996; Pimentel et al., 1998a). Currently, food shortages are critical, with more than 3 billion humans malnourished worldwide — the largest number and proportion ever (FAO, 1992a, b; Neisheim, 1993; McMichael, 1993; Maberly, 1994; Bouis, 1995; WHO, 1995; WHO 1996). An estimated 40,000 children die each day due to malnutrition and other diseases (WHO, 1992).
The planet’s numerous environmental problems emphasize the urgent need to evaluate the available environmental resources and how they relate to the requirements of a rapidly growing human population (Hardin, 1993; Cohen, 1995). In this article we assess the carrying capacity of the Earth’s natural resources, and suggest that humans should voluntarily limit their population growth, rather than letting natural forces control their numbers for them. (Pimentel et al., 1994a; Bartlett, 1997-98). In addition, we suggest appropriate policies and technologies that would improve the standard of living and quality of life worldwide.

Population Growth and Consumption of resources
All of our basic resources, such as land, water, energy, and biota, are inherently limited (Lubchenco, 1998). As human populations continue to expand and finite resources are divided among increasing numbers of people, it will become more and more difficult to maintain prosperity and a quality of life, and personal freedoms will decline (UNFPA, 1991; RS and NAS, 1992; Rees, 1996).
During recent decades there has been a dramatic worldwide population increase. The U.S. population doubled during the past 60 years from 135 million to more than 270 million (NGS, 1995) and, based on the current U.S. growth rate of approximately 1% per year (USBC, 1996), is projected to double again to 540 million in the next 70 years . China’s population is 1.3 billion and, despite the governmental policy of permitting only one child per couple, it is still growing at an annual rate of 1.2% (SSBPRC, 1990).
India has nearly 1 billion people living on approximately one-third of the land of either the United States or China. India’s current population growth rate is 1.9%, which translates to a doubling time of 37 years (PRB, 1996). Together, China and India constitute more than one-third of the total world population. Given the steady decline in per capita resources, it is unlikely that India, China, and the world population in total will double.
In addition to limitations due to population increases, high per capita consumption levels in the United States and other developed nations also put pressure on natural resources. For example, each American consumes about 50-times more goods and services than the average Chinese citizen (PRB, 1996). Americans consume more goods and services because of relatively abundant per capita land, water, energy, and biological resources, as compared to the Chinese (Table 1). Achieving an average European standard of living ($12,310 per capita/yr) or an average U.S. standard of living ($26,000 per capita/yr) appears unrealistic for most countries because of serious shortages of the basic natural resources (PRB, 1996). This does not imply that both developed and developing countries can not use their resources more efficiently than they are at present through the implementation of appropriate policies and technologies.
Thus far, the relative affluence enjoyed by most Americans has been possible because of an abundant supply of fertile cropland, water, and fossil energy. As the U.S. population continues to expand, however, resource shortages similar to those now being experienced by China and other developing nations will become more common (Tables 1 and 2). Accelerated declines in the U.S. standard of living are likely if the U.S. population increases as projected during the next 70 years, from 270 million in 1998 to 540 million (Grant, 1996; Pimentel and Pimentel, 1996).'

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