U.S. Population Growth versus Environmental Resources

by David and Marcia Pimentel

The high cost of fuel at the gas pump is alerting Americans that fossil fuel does run our lives. Other emerging problems are related to adequate cropland and freshwater for food, plus the global warming threat. Too often ignored is the adverse effect of human population expansion on all of these essential environmental resources.

In a mere 7 years, the U.S. population has expanded 10%, from 270 million to 300 million. In the next 70 years, U.S. population is projected to double to about 600 million, based on its current growth rate of 1.1%. Put another way, U.S. population will double in just 70 years. This present rate of our population growth is nearly twice that of China. However, because of the volatile issues surrounding U.S. immigration policies, it is conceivable that the population may easily exceed the projected 600 million in 70 years.

Thus far, the vast environmental resources of the United States have been sufficient to support the American lifestyle. Genuine concern is growing as to how human numbers and human needs are outpacing the availability of vital basic resources. Problems include: providing future food security, maintaining human health, protecting environmental integrity, and insuring personal freedoms.

The major resources required for a secure American food supply include fertile land, freshwater, biodiversity, and several fossil energy resources. In diverse ways these same resources support housing, industrial development, the transport systems, and other activities considered important by most Americans. Some people are beginning to wonder how many people can be supported by U.S. natural resources without catastrophic degradation of the environment, and whether we will be able to move to a sustainable solar energy system.

To reach sustainability, we estimate an optimal U.S. population would be 100 to 200 million people for a suitable, European living standard.

LAND FOR AGRICULTURE

To feed the rapidly growing human population, food yields must continue to increase; to achieve this goal, fertile cropland is vital. At present, the U.S. is fortunate to possess 0.5 ha (2.5 acres per hectare) of cropland per person, an area considered a minimum to provide a diverse food supply. In contrast, worldwide cropland per person has diminished to only 0.23 ha. As human numbers escalate and their activities cover over the land, cropland is lost. As this loss continues, food production for future generations will be in jeopardy

Cropland must have fertile soil. As the soil is used, soil quality diminishes unless great care is practiced. For example, if soil is left unprotected without biomass cover, it is susceptible to loss by the energy in heavy rains and winds. Then severe soil erosion takes place and the productivity of the soil declines. Eroded soil loses its water content, nutrients, and soil organic matter, all vital components for plant growth. Soil erosion is often a slow and unnoticed activity, but 1 mm can be easily lost during one rain or windstorm. Under agricultural conditions 500 years are required to replace 2.5 cm (1 inch) of valuable topsoil.

Each year more than 1 million hectares of U.S. cropland is destroyed by erosion and has to be abandoned. All too often, valuable forestland must be cleared to replace the eroded cropland.

To protect soil quality, major conservation techniques, like crop rotations and cover crops, need to be practiced to insure the conservation of soil fertility.

WATER

Freshwater is essential for the survival of all living organisms, including humans, plants, and microbes. Indeed rainfall provides all the water required for the diversity of life on earth.

Agriculture is the major consumer of water in the U.S. and is now using 80% of available freshwater. Approximately 1,000 mm of rainfall, spread over most of the year, is needed for successful crop production.

In traditionally arid regions, with 500 mm or less rainfall, irrigation must be used. Crop irrigation not only requires large amounts of water from stored sources, but also enormous amounts of fossil energy to pump and apply the water. In many arid regions, large aquifers provide this water. As overall water demands increase, more water is being pumped from the aquifers and their capacity is reduced. In one region of Arizona, water is being removed from aquifers 10 times faster than the recharge by rainfall. Because irrigation is costly, farmers in some regions must abandon the growing of low value crops, like alfalfa, and replace them with higher value crops, like cotton.

Pollution of water is increasing due to wastes produced from industry, agriculture, and urban areas. The EPA reports that 40% of U.S. lakes are not suitable for swimming because of severe pollution.

All freshwater supplies must be shared by people, for their agricultural and other activities. For example, the 7 states that border the great Colorado River use its water not only for basic human needs, but also for agriculture. As human numbers grow so does the pressure on all water resources, as conflicts between users intensify.

ENERGY

Throughout history, significant quantities of energy have been expended for agriculture. The ever-present solar energy was first augmented by human and animal power. Water and wind power were developed. In about 1850 when sufficient and cheap fossil energy, like coal, oil, and natural gas became available, their use increased and become widespread. For crop production, energy is used not only in producing and operating the farm equipment, and in powering irrigation systems, but also in the manufacture of fertilizers and pesticides.

Society has drawn down the supplies of oil through frequent and widespread overuse. Petroleum geologists report that the peak production of oil and natural gas sources has been reached and now their supplies will be declining. Fossil energy (oil, natural gas, and coal) is a finite resource. Americans, who represent only about 4% of the world population, use 25% of the world’s fossil energy, or more than any other country in the world. Furthermore, the U.S. is now importing more than 63% of its oil and most of its natural gas.

Fortunately, the U.S. currently has ample supplies of coal that are projected to last from 50 to 100 years. But coal is more polluting than oil and natural gas, and contributes greatly to global warming. Nuclear energy does not add to global warming, but has significant other environmental problems associated with its use.

RENEWABLE ENERGY

With more than 90% of U.S. oil resources depleted and now having to rely on oil and natural gas imports, Americans are beginning to evaluate the potential of renewable energy sources for the future. Captured solar energy is promising as a source for electricity, heat, and the production of hydrogen as a potential liquid fuel. Possible energy sources are photovoltaics, wind power, hydropower, biomass thermal, solar thermal, and geothermal. Most and probably all solar energy systems will need improvement and increased efficiency. New and improved storage systems, like batteries, would be a major help.

However, it should be emphasized that to produce just half of U.S. current energy consumption by renewable energy would require 17% of total U.S. land area, and this area is equal to the total land area currently in crops.

Using biomass requires not only large areas of land, but also water and additional energy, for management. In particular, the use of corn to produce ethanol requires significant amounts of fossil energy input, and thus is not a practical solution for liquid fuels. Currently, the U.S. is producing 3.4 billion gallons of ethanol per year (DOE). This amount represents only 1% of total U.S. vehicle fuel use per year while using 14% of U.S. corn production. If 100% of U.S. corn were used, the ethanol produced would provide only 7% of current U.S. vehicle fuel use. Will this make the U.S. oil independent? Converting cellulosic biomass in ethanol requires more fossil energy input than producing ethanol using corn. Thus, woody biomass will not provide an adequate supply of liquid fuel.

To balance the potential contribution of solar energy production and supply in the future, Americans will have to reduce their overall energy consumption by 50%.

BIODIVERSITY

Often not recognized as important in agricultural production are the roles natural plants, animals and microbes play in agriculture and in every day life. For instance, one third of all food crops depend on pollinators, like wild bees and honeybees. Earthworms help in soil formation, enhance the percolation of water into the soil, and along with microbes help in the recycling of organic wastes. Some insect species and microbes contribute to the biological control of pests, thus saving an estimated $10 to $12 billion each year in pest control.

Biodiversity loss throughout the world, as well as in America, is escalating because of the more than 100,000 different chemicals used in agriculture, gardens, and industry. Further, the continued expansion of human activities continues to destroy the natural habitats vital to the preservation of species.

In this era of global trade and travel, organisms of all kinds are being transferred and introduced into new environments. Some of these ”invader” organisms become pests and damage their new ecosystems. In fact, invaders cause about 40% of the current loss of U.S. crops. The National Park Service recently reported that more than 100 species of invading plants have become established in the Colorado area. Bark beetle species, in particular, are killing vast numbers of trees throughout the Western United States. A comprehensive program of educating the public and screening goods and materials brought into the U.S. should be implemented to prevent future damage to our crops, livestock, and public health.

FUTURE OUTLOOK

The force of population expansion is destroying the earth’s resources faster than any time in history. Based on the current unprecedented high U.S. immigration rates, the previous projection of 600 million in 70 years appears too conservative and we project a population of at least 700 million by 2075.

Population numbers will determine how quickly essential resources of cropland, freshwater, and biodiversity are reduced. Energy in its many forms emerges as a major limiting factor in the future. Conservation is now vital.

Working together, Americans can take action to ensure that future generations can enjoy a quality and safe life, with their personal freedoms protected.

David Pimentel is a professor of ecology and agricultural sciences at Cornell University. His Ph.D. is from Cornell University; postdoctoral study at Oxford University and University of Chicago. His research spans the fields of energy, ecological and economic aspects of pest control, biological control, biotechnology, sustainable agriculture, land and water conservation, and environmental policy. Pimentel has published more than 600 scientific papers and 24 books. He has served on many national and government committees including the National Academy of Sciences; President’s Science Advisory Council; U.S Department of Agriculture; U.S. Department of Energy; U.S. Department of Health, Education and Welfare; Office of Technology Assessment of the U.S. Congress; and the U.S. State Department.

Marcia Pimentel is a senior lecturer in the Division of Nutritional Sciences at Cornell University. Her B.S. and M.S. degrees are from Cornell University. Her research has dealt with food science and nutrition, environmental resources, and population and society. She has published more than 60 scientific papers and 3 books.

Americans, who represent only about 4% of the world population, use 25% of the world’s fossil energy, or more than any other country in the world. Furthermore, the U.S. is now importing more than 63% of its oil and most of its natural gas.

Currently, the U.S. is producing 3.4 billion gallons of ethanol per year (DOE). This amount represents only 1% of total U.S. vehicle fuel use per year while using 14% of U.S. corn production. If 100% of U.S. corn were used, the ethanol produced would provide only 7% of current U.S. vehicle fuel use.