“For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.”

Richard Feynman



by David Pimentel of Cornell University and Mario Giampietro Istituto of Nazionale della Nutrizione, Rome

Executive Summary Released November 21, 1994

For copies of the full report contact:
Carrying Capacity Network 2000 P Street, N.W., Suite 240 Washington, D.C. 20036 (202) 296-4548


The following two pages are highlights of the study, “Food, Land, Population, and the U.S. Economy” by Drs. David Pimentel of Cornell University and Mario Giampietro of the Istituto Nazionale della Nutrizione, Rome. This comprehensive assessment of U.S. population growth and its impact on America’s agricultural productivity was commissioned by Carrying Capacity Network (CCN), a non-profit organization in Washington, DC which focuses on the interrelated nature of the economy, population growth, and environmental degradation.


  • At the present growth rate of 1.1% per year, the U.S. population will double to more than half a billion people within the next 60 years. It is estimated that approximately one acre of land is lost due to urbanization and highway construction alone for every person added to the U.S. population.
  • This means that only 0.6 acres of farmland would be available to grow food for each American in 2050, as opposed to the 1.8 acres per capita available today. At least 1.2 acres per person is required in order to maintain current American dietary standards. Food prices are projected to increase 3 to 5-fold within this period.
  • If present population growth, domestic food consumption and topsoil loss trends continue, the U.S. will most likely cease to be a food exporter by approximately 2025 because food grown in the U.S. will be needed for domestic purposes.
  • Since food exports earn $40 billion for the U.S. annually, the loss of this income source would result in an even greater increase in America’s trade deficit.
  • Considering that America is the world’s largest food exporter, the future survival of millions of people around the world may also come into question if food exports from the U.S. were to cease.


Drs. Pimentel and Giampietro have concluded that U.S. population growth is a primary cause of these harsh potential outcomes. The study explains that the United States is the fastest-growing industrialized country in the world, now increasing by approximately three million people per year. This population growth rata is equivalent to adding 58,000 people per week or a city the size of Washington, D.C. to our country every year. The overall growth rate of the U.S. population has escalated in large part because of the unprecedented number of immigrants that have been allowed to come into the United States and their disproportionately higher birth rates compared to the native-born. About half of U.S. population growth is currently the result of immigration.


Land: On-going soil erosion and expanding urbanization contribute to the continuous loss of cropland in the U.S. Annually, more than two million acres of prime cropland are lost to erosion, salinization, and waterlogging. In addition, more than one million acres are removed from cultivation as America’s limited arable land is Overwhelmed by the demands of urbanization, transportation networks, and industry. As a result of arable land shortages, U.S. meat consumption may be reduced.

Water: The groundwater that provides 31% of the water used in agriculture is being depleted up to 160% faster than its recharge rate. The vast U.S. Ogallala aquifer (under Nebraska, Oklahoma, and Texas) will likely become non-productive within the next 40 years. Even if water management is substantially improved, the projected 520 million Americans in 2050 would have about 700 gallons/day/capita, considered the minimum for all human needs, including agriculture.

Energy: The availability of non-renewable fossil energy explains in part the historically high productivity of U.S. agriculture. Currently the 400 gallons of oil equivalents expended to feed each American amount to about 17% of all energy used in this country each year. Yet given current use levels, only 15 to 20 years of oil resources remain in the U.S. Although imports now account for 58% of oil used in the U.S., these international reserves are expected to be exhausted within the next 30 to 50 years.


Given current depletion rates of land, water, and energy resources, U.S. agricultural productivity is already unsustainable. Should the U.S. population double within the next 60 years, the subsequent decrease in arable land will substantially change American eating habits and dramatically reduce future food exports. If Americans want continued access to abundant and affordable food with the ability to continue exporting food, we must work together to stop U.S. population growth and conserve our country’s limited land, water, and energy resources in order to achieve a sustainable American future.

*carrying capacity refers to the number of individuals who can be supported without degrading the natural, cultural, and social environment, i.e. without reducing the ability of the environment to sustain the desired quality of life over the long term.


Population growth reduces self-sufficiency in food, availability of vital natural resources, standard of living, and ultimately U.S. national security. The United States is in a privileged situation compared to many other nations in the world because its per capita endowment of natural resources is relatively high based on its current population density. However, the United States is at serious risk of losing this privilege if attention is not given to the control of population growth (including immigration), the sustainable management of natural resources, and the development of alternative energy sources. Food security depends on ample fertile land, fresh water, energy, and protecting biodiversity of plant and animal species.

Native-born Americans are reproducing at about replacement level. However, the overall growth rate of the U.S. population has been escalating during the past decade in large part because of the unprecedented number of immigrants that have been allowed to come into the United States and their high birth rate (Figure 1). Since the 1950’s, the U.S. population has grown from 150 to 260 million. This means that about 3 million people are being added each year or 58,000 per week. About half of this increase results from our liberal immigration policy. At the present growth rate of 1.1% per year, the U.S. population will double to about 520 million within the next 60 years. Such a major expansion will dramatically decrease per capita availability of all the resources that support human life. Significant changes in food availability, type of diets, food costs, food exports, and food security will follow.

Consider also that 36 million Americans now live in poverty and many of these do not have sufficient food. The number in jeopardy continues to grow and gives further evidence that our food situation will worsen as our population grows and all resources, including food, become in shorter supply than ever before.

To clarify the extent of the problems concerning land and food supply we surely will face in 2050, an assessment is made of the carrying capacity of available land, water, and energy resources-all vital to achieving an adequate supply of food. Balanced against these, are the impacts a doubling of the U.S. population can be expected to inflict on these natural resources.

Land Resources

Arable land, with its fragile top 6 inches of fertile soil, determines the productivity of our food system. More than 99% of U.S. food comes from this land while less than 1% comes from aquatic systems 1. Of the 2.3 billion acres of U.S. land, only 20% is sufficiently fertile for crop production 2. Most land is either too dry, wet, steep, or cold for crop production. Approximately 26% of our land is used to pasture livestock, 25% for forestry 3, while the remaining 29% is deserts, mountains and devoted to urbanization and highways.

Nearly 400 million acres of arable land now are in cultivation in the U.S. to produce our food. Included are about 215 million acres planted to grains. Of this, 68 million acres are used for food products and 68 million acres for livestock feed. The remaining nearly 80 million acres are planted to corn, wheat, rice, and other grains for export. These exports give a return of about $40 billion per year. Fortunately, an additional 70 million acres suitable for crop production are held in reserve and are not being used at present 4.

On a per acre basis the United States now has 1.8 acres of cropland resource per capita to provide Americans with an ample diet of plant and animal products (Figure 1) (Table 1).

Not only does population expansion reduce available cropland per capita, but on going soil erosion and expanding urbanization continually result in the slow but continuous loss of cropland. Annually, more than 2 million acres of prime cropland are lost to erosion, salinization, and waterlogging. In addition, more than I million acres are lost from cultivation as urbanization, transportation networks and industries take over croplands.

Soil erosion, whether by wind or water, occurs when vegetative cover is removed from land and also when conservation practices are not implemented by farmers. Erosion not only depletes the soil of nutrients and water resources, but also removes soil organic matter and beneficial soil biota, which are essential for maintaining a productive soil.

The natural replacement of fertile soil is infinitesimally slow. For example, it takes about 500 years to replace just 1 inch of soil. Depending on the area of the country, wind and water erosion are reducing productivity of U.S. soils from 5 to 65% each year. For instance, Iowa, a prime agricultural state, has lost one-half of its topsoil after farming for about 100 years. There, soil is being lost about 30 times faster than the natural formation rate.

Furthermore, soil erosion removes about $20 billion worth of plant nutrients from U.S. agricultural soils each year. At present these nutrients are being replaced by heavy applications of expensive, fossil energy-based fertilizers. Other fossil-based inputs, like pesticides and fossil-powered irrigation systems also are being used to offset soil degradation. Once land becomes seriously degraded and unproductive, however, farmers are forced to abandon it and look elsewhere for more land to cultivate. However, this option will not be possible in the future, because there will be no more land to move into agriculture.

Water Resources

Direct rainfall and that collected in rivers, lakes, and ground provide the freshwater supply needed by individuals, industry, and agriculture. Agriculture, the major consumer of water, uses about 85% of all U.S. freshwater resources pumped from storage sources. All crops utilize and transpire massive amounts of water during growth, fruit and seed production. For example, a corn crop that produces about 118 bushels/acre/year of grain takes up and transpires more than 500,000 gallons/acre of water during the growing season. To produce 1 pound of corn grain requires about 1,400 pounds (175 gallons) of water for its production.

Surface water supplies depend on rainfall and thus vary according to the climate of a particular region. Although periodic droughts are common in all parts of the United States, many western states are considered to be arid, based on their annual rainfall. To provide the ever increasing amounts of water needed for all human activities, overdraft is occurring from many surface water resources, especially in the west and south. For example, by the time the Colorado River enters Mexico it has literally disappeared because the states of California, Arizona, and Colorado have removed excessive quantities of water to meet their local needs and return little or no water.

In the United States, surface water supplies about 60% of the water used in irrigation, with the remainder coming from ground water supplies. Ground water is referred to as fossil water because it accumulates in aquifers deep below the surface and once removed is replenished only very slowly. That is, less than 0.1% of the stored ground water mined annually by pumping is replaced by rainfall. The overdraft of U.S. ground water averages 25% greater than its rate of replacement. But in some locations, like the vast U.S. Ogallala aquifer, which stores water for Nebraska, Oklahoma, and Texas, the annual overdraft is 130% to 160% above its replacement rate. If this is allowed to continue, the Ogallala will probably become non-productive within the next 40 years. Thus, the Ogallala and all ground water resources must be carefully managed to prevent their overdraft and subsequent depletion.

On arid crop lands, convenient water supplies from lakes, rivers, and aquifers are pumped for irrigation to make crop production possible. Irrigation costs 2 to 5 times more per acre than rainfed crop production in both equipment and fossil energy needed to power the application of the water. Therefore, farmers generally irrigate only when no alternatives are available or the irrigation cost is subsidized. Note, the U.S. government is currently spending about $4 billion annually to subsidize irrigation in our western states.

Energy Resources

The availability of non-renewable fossil energy is supporting the high levels of crop production now being enjoyed by U.S. agriculture. Thus far, production has been able to keep up with the food needs of our expanding population. Fossil energy also powers our vast transportation system and industrial development. As important, its availability has improved the quality of life, protecting humans from numerous diseases. For example, many diseases are transmitted via water, and the availability of energy makes possible the purification and delivery of clean water. Fossil fuels are used in processes to remove sewage and to process wastes before they are returned to the environment. Pesticides, produced from petrochemicals, play a major role in protecting crops from pests and controlling vectors of human disease, e.g. mosquito vectors of encephalitis.

Fossil energy use in all U.S. economic sectors has increased from 20 to as much as 1000-fold in just 4 decades. U.S. citizens consume 20 to 30 times more fossil energy per capita than most people in developing countries. Since 1945, energy for agricultural use has increased about 4-fold while crop yields have increased about 3-fold. Currently the 400 gallons of oil equivalents expended to feed each American amount to about 17% of all energy used in this country each year.

Fossil fuels are finite, meaning their supply is subject to depletion and more importantly once gone, they can not be replenished. The estimates concerning future availability of fossil fuels are discouraging, especially for oil and gas. Government reports indicate that only 15 to 20 years of oil resources and 20 to 30 years of natural gas reserves remain, given current use levels. Note, Alaska peaked for its oil production in 1988 and oil reserves are expected to be depleted by 2015. U.S. oil production has been declining by 400,000 to 500,000 barrels per year. To augment the diminishing supply, the U.S. now imports 58% of its oil from the Middle East and other areas which are estimated to have reserves lasting from 30 to 50 years. The diminishing levels of oil and gas reserves become more critical each year and indicate a serious energy problem already exists here. Furthermore, U.S. reliance on foreign oil causes a negative balance of trade payments and obscures the realization of how serious the domestic fossil fuel situation is. Fortunately, U.S. coal reserves, projected to last about 100 years, give some time in which to develop renewable energy systems. Meanwhile the burning of coal resources creates serious environmental pollution problems which need to be overcome.

Environmental Costs of Agriculture The use of inappropriate agricultural practices, like large monocultures and removal of shelterbelts, contributes to serious wind and water erosion. Soil and water losses are responsible for significant economic and environmental on-site costs in U.S. agriculture. Each year the estimated 4 billion tons of soil and 130 billion tons of water lost from 400 million acres of U.S. cropland translate into an on-site economic loss of more than $27 billion. The most significant component of this cost is the loss of valuable soil nutrients, which must be replaced by increased applications of fossil-based fertilizers in order to maintain and augment yields.

In addition, erosion causes a loss of biodiversity that is impossible to quantify in terms of dollars, although preservation of soil biota is of major benefit to maintaining soil quality and productivity. Erosion causes significant ecological damage, in the form of siltation of aquatic systems and destruction of stream and lake ecosystems. Frequently, some pesticides and fertilizers contained in eroded agricultural sediments may poison fish and other wildlife.

Erosion damages extend beyond the cultivated land far into the surrounding environment. Off-site costs include: roadway, sewer, and basement siltation; disruption of drainage; undermining of foundations and pavements; gullying of roads; earth dam failures; eutrophication of waterways; siltation of reservoirs and harbors and channels; general flooding; damage to public health from blowing dirt; plus increased water treatment costs. Remedies for such damages require substantial expenditures by individuals and governments. The combined yearly cost of all off-site damages caused by erosion is estimated to be about $17 billion.

Food Produced and Consumed

With a population of about 260 million people, most Americans enjoy a high standard of living and an abundance of relatively cheap food. The average yearly income per family in the United States is nearly $30,000 compared with only $4,000 per family in developing countries. About 15% of U.S. income is spent on food, whereas in most developing countries the amount spent on food ranges from 50% to 60%.

The average American consumes about 2,175 pounds of food per person per year, which provide about 3,600 Calories of food energy per day. This daily intake contrasts with the worldwide average of 2,700 Calories.

Americans eat large amounts of animal products, totaling nearly 800 pounds per person per year, including dairy products. Approximately one-third of their calories is from animal sources and two-thirds from plant sources (Table 1). These animal products contribute excellent protein quality to the diet, but increase the fat intake of the average American to about 40% of the calories consumed.

In addition to all the food consumed by Americans, approximately 20% of all food produced, especially grains, is exported. At present, food crops represent a major U.S. export, and thereby help to diminish the deficit in our trade balance, caused in large measure by oil imports.

Self-sufficiency in food production and availability of basic resources, especially expensive fossil energy, support the high standard of living currently enjoyed by most Americans.

Future Food Security and Population Growth

Population in 2050

At the current rate of increase of 1.1% per year including legal immigration, the U.S. population is projected to double and reach more than 520 million by the year 2050. If this growth rate does not increase further, as it has recently, by the year 2100 the United States will have a population of 1 billion or a population similar to that existing now in China. For this analysis, however, the focus is on the year 2050.

Land Resources

Over the next 60 years both erosion and urbanization will diminish our arable land base of 470 million acres. Currently 2 million acres per year are lost from production because of erosion, salinization, and waterlogging. Based on this rate of loss, 120 million acres are projected to be lost during the next 60 years. No doubt some of this unproductive land will be replaced, but most probably with marginal land, the type that requires substantial fossil-fuel inputs of fertilizers, pesticides, and irrigation to maintain crop productivity.

Often overlooked is the continuous impact of urbanization and transportation systems on arable land resources. Over the past 200 years, for instance, the expansion of these systems has covered 260 million acres, approximately half of which was arable land. Thus, about 1 acre of land has been used for urbanization and highways by each person added to the U.S. population. Based on this average rate of expansion, the doubling of the U.S. population can be expected to use up an additional 250 million acres, with half being arable land. This means our vital arable land resource will be significantly affected by the expansion of urbanization and highways throughout the country. Even assuming that in the future the arable land lost to these processes will approach half an acre per capita, which is approximately the current rate of expansion in Europe, still 60 million acres of arable land will be taken out of production.

The combined reduction of 60 million acres by urbanization and the 120 million acres lost to production because of erosion, leaves the United States only about 290 million acres of arable land. Based on these projected trends and the expanded population, only 0.6 acres of arable land per person will be available in 2050 (Table 1). Agronomists, however, stress that more than 1.2 acres per person are needed for a productive agriculture, one that produces a varied diet of plant and animal products. Faced with this major reduction in per capita arable land, production patterns will have to be altered to include increased production of grains, legumes, and tubers, while animal production will be sharply curtailed. Then the U.S. diet will shift from a mixed plant/animal diet to primarily a vegetarian diet, and certainly one with less variety of choice than we presently enjoyed.

Furthermore, experience has demonstrated that the intensive management of land to increase crop yields increases soil erosion. Then too, as more marginal land types have to be put into production to compensate for land shortages, erosion will worsen. If available and affordable, more fossil-based fertilizers and pesticides will have to be used to insure ample harvests, thereby increasing environmental pollution.

If techniques are developed to slow soil erosion by employing various soil and water conservation practices, the supplies of water and energy resources could be extended and give us more time to develop ecologically sustainable practices. Unfortunately, the history of soil and water conservation practices in the United States and world is discouraging.

Water Resources

Americans currently use about 1,450 gallons/day/capita (g/d/c) for all their needs, with the largest amount expended in agriculture. If water management is substantially improved, the projected 520 million Americans will have about 700 g/d/c in 2050 (Table l). Hydrologists consider 700 g/d/c minimal for human needs, including water for adequate food production. Clearly Americans will have to make major adjustments in their water use, especially in the arid regions of the nation. There is no technology available that is able to double the flow of the Colorado River to insure a viable river flow reaches Mexico. Indeed, the major users of this and other rivers will have to find ways to share, as each tries to cope with increased demands for water.

In addition, irrigation will, of necessity, decrease as our ground water resources continue to be mined and the water resources have to be divided among more people. As mentioned, at its present rate of use, the Ogallala aquifer will become significantly less productive during the next 50 years. Because arid sections of our western and southern states already are experiencing increased water shortages, we can expect some agricultural production to shift from these regions to the midwest and northeast where rainfall is relatively abundant. Such a major reallocation of production will impose other constraints on the U.S. food production as a whole and on the variety of foods available in the consumer market.

Energy Resources

Because the projected 15 to 20 years of oil reserves remaining is based on current consumption rates, the continued growth of the population makes this projection uncertain. The United States currently imports 58% of its oil, creating an annual trade debt of more than $70 billion and this reflects not only our high consumption levels but also the depletion of domestic oil supplies. By 2000, U.S. oil imports are expected to increase to about $100 billion per year, while food exports will diminish as more food is needed domestically. Then the U.S. trade imbalance will worsen as food exports, especially grains, decrease. Approaching 2050, most of the oil and natural gas in the United States will be exhausted and world supplies will be ever closer to depletion. Coal will be the remaining fossil fuel. Although coal can be used to produce oil and natural gas, it is expensive to convert to usable liquid and gaseous fuels and its use is extremely polluting. However, once coal becomes the major fuel, its supplies will experience heavy use, thereby speeding the depletion of that finite resource.

At present, nuclear energy does not represent a safe and reliable alternative to oil because of its problems with radioactive waste disposal and safety. Furthermore, it is not a renewable energy system because uranium fuel is consumed in nuclear fission plants and uranium is a finite resource. In contrast, nuclear fusion technology is a renewable energy system, and may eventually be developed. If so, it will augment the energy supply. However, this technology also has serious limitations, including the enormous amounts of radioactivity and waste heat it produces. The inevitable conclusion is that future energy supplies will become increasingly limited, not only for use in food production but for all human activities.

The transition to renewable energy systems, like solar energy, certainly can be achieved, but will take several decades for their full development. In addition to access to sunlight, solar systems need significant expenditures of fossil energy as well as large quantities of other material resources. Furthermore, all known solar energy technologies require large acreages of land for the collectors that capture the dilute solar energy. Estimates are that about 20% of U.S. land area (about 450 million acres) would be required to support a solar energy system that would supply but one-half (37 quads) of our current energy consumption (80 quads). This land requirement can be expected to diminish arable, pasture, and forest lands to some extent, with the most critical loss being arable land.

Faced with double population numbers, solar energy systems will be able to provide only one-quarter of the current per capita energy consumption or about 600 gallons of oil equivalents (Table 1). Clearly this will require a drastic decrease in energy use and no doubt will adversely affect the U.S. standard of living, including food availability. Meeting energy needs based on solar energy will cause major competition between land needed for energy production, crop and livestock production, forestry production, and urbanization. Given the need for food, agriculture and the entire food system will remain a high priority in the use of the remaining fossil energy.

Sustainability of Agriculture

U.S. agriculture is not sustainable based on current cultivation practices and resources for the following reasons: (i) soil nutrients (nitrogen, phosphorus, potassium, and calcium) are removed from the land when crops are harvested and when soil is eroded from the land; (ii) these nutrients are being replaced with the use of fos the effective management and exploitation of various natural resources, but technology cannot increase the flow of natural resources. For instance, increasing the size and number of fishing vessels has enabled us to overfish our oceans. However, larger and more numerous fishing vessels does not increase fish populations, if fact it is causing their decline. There is no technology that will double the flow of the Colorado River. In addition, using more chain saws causes a decrease in forest production and does not increase tree growth.

Food Supply and Costs

By 2050, when crop land is projected to decrease to about 0.6 acre and pasture land to 1.1 acres per capita, food production will be reduced (Table 1). Even if all food exports are eliminated, the diet of the average American will, of necessity, include more grains, legumes, tubers, fruits, and vegetables and significantly less animal products. According to nutritionists this can be a more healthful diet than our current diet of high animal products. Yet, the freedom of choice in our diet as we enjoy today will be restricted.

It follows that the increased need for food will significantly increase the price of food, because of the inelasticity of food prices. That is, for every 1% increase in demand of food, the price at the farm gate increases 4.5%. Even with some reduction in food consumption and decreased use of animal products, food prices are expected to increase 3 to 5 fold (Table 1). Then Americans may be spending from 30% to 50% of their income for food which is typical at present in Europe and other developed nations.


Food security for the United States and quality of life are directly affected by the natural resources at our disposal, their level of use, and the number of people who must share them. The United States has been fortunate to possess superior supplies of these resources. Perhaps it is this wealth that has made Americans great consumers of resources. Our use of water supplies and especially the consumption of fossil fuels, compared with other countries illustrate these use patterns.

This analysis has emphasized the on going depletions of land, water, and energy resources. These losses are expected to increase in future decades as the U.S. population doubles and its needs for these resources concurrently increase.

Given the fact that the supply of natural resources is finite and that the ability of technology to replace many of these resources is limited, we are left with the necessity of controlling population numbers. Certainly, diminishing consumption levels by stringent conservation programs will help slow depletion. But individual responsibility on the part of men and women to control family size is vital to control population numbers and maintain a high standard of living, otherwise the harsh realities of nature will impose its control on the population.


1. Per capita fish production from aquatic systems will continue to decline because of overfishing, pollution, and population growth.

2. Combined, crop and pasture land occupy 50% of the U.S. total land area. This amount of land is essential to provide the diverse diet Americans presently enjoy. However, if the U.S. population doubles in about 60 years, Americans will have a less varied diet, one consisting mostly of grains and vegetables.

3. Additional forests should not be converted into agricultural and urban uses because forest products are already in short supply. U.S. forests also are essential in preventing flooding, purifying water, and removing carbon dioxide from the atmosphere.

4. This 70 million acres in reserve represents less than 0.7% of U.S. agricultural land. This small amount of land is insufficient to rescue agriculture when the population doubles.

ResourceCurrent Population
(260 million)
2050 Population
(520 million)
Arable Land1.8 acres0.6 acres
Pasture Land2.3 acres1.1 acres
Forest Land2.2 acres1.0 acres
Fresh Water1,300 gallons700 gallons
Energy2,500 gal oil equivalents a1,600 gal oil equivalents b
Food Exports$155$0
Foodanimal + 69% plantanimal + 85% plant
Food CostsCurrent level3- to 5-fold increase

Table 1.
Current and future resources for U.S. food production and costs of food per capita.

a. Current energy consumption is mainly from fossil energy sources.

b. Estimated supply of energy from renewable sources.