Humans, like all organisms on Earth, interact with both the biotic (living) and abiotic (nonliving) factors in their environment. Environmental degradation occurs when a potentially renewable resource—one of the biotic or abiotic factors humans need and use—such as soil, grassland, forest, or wildlife—is extracted at a rate faster than the resource can be replaced, and thus becomes depleted. If the rate of use of the resource remains high, the resource can become nonrenewable on a human time scale or even become nonexistent.
For example, topsoil is important to farmers because crops are grown in topsoil. It can take as many as 200 years to form 1 centimeter (0.40 inches) of topsoil through natural processes. Topsoil can also be lost through various causes. One of the main causes of topsoil loss is erosion. Erosion can happen when water washes soil downhill or when wind blows unprotected soil away. Worldwide, topsoil is being lost to erosion much more quickly than it is being replaced.
If topsoil loss is allowed to continue unchecked, the land can be rendered permanently infertile through a process known as desertification. Many areas of the world suffer from desertification. Grasslands do not receive much rain. If the soil cover is removed by overgrazing or by poor farming practices, the topsoil can be rapidly removed by wind erosion. This happened in parts of Texas and Oklahoma during the 1930s, leading to dust-bowl conditions. Although drought contributed to dust-bowl formation, the main cause was overgrazing and poor farming practices.
Loss of biodiversity is an important aspect of environmental degradation. Biologists agree that species are becoming extinct at an alarming rate. Biodiversity is also being lost at the ecosystem level due to environmental degradation. Tropical forests are recognized as the most diverse ecosystems on Earth and are experiencing the highest rate of ecosystem loss, but temperate habitats are also suffering degradation. Because the temperate parts of the world were settled first, the loss of biodiversity has been greatest there.
The quantitative loss of ecosystems is easy to measure. When a native prairie is converted to a cornfield or an open field is paved over to make a parking lot, the number of hectares can easily be calculated. Qualitative ecosystem degradation is harder to measure. The structure, function, or composition of an ecosystem can slowly change until the habitat is lost.
The Population Factor
Who is responsible for degrading the environment? We all are. Ordinary human activity from even the most responsible individuals inevitably pollutes and degrades the environment to some extent. We degrade the environment directly when we consume resources (for example, burning wood in a fireplace), and indirectly when we extract resources and transform them into products we need or want.
In 1999, the number of people on Earth exceeded 6 billion. The population of the world increased fourfold in the twentieth century. This rapid increase in population was accompanied by an even more rapid increase in the use of resources to support the growing population and to raise living standards. During the twentieth century, global energy use increased by a factor of 20. Following World War II, the world became even more dependent on extractive industries, such as mining and oil exploration, to supply the various minerals and fossil fuels required to support a higher standard of living. Energy shortages have an even greater impact on developing nations that are heavily dependent on subsidized fuel supplies to maintain food production.
The role of agriculture.
During the twentieth century, agriculturally productive land has been extensively modified to make it even more productive. This includes the widespread use during the twentieth century of chemical fertilizers (often produced from oil) pesticides, and extensive irrigation. To supply the needs of extensive irrigation, surface water has been diverted and many wells have been drilled seeking ever more subsurface water. At the same time that industrial agriculture was growing, agriculturally productive land was being lost to urban development and industry. In the twenty first century, competition for remaining land and water resources is expected to continue to increase.
Modern agriculture has been able to produce an enormous amount of food. Intensive agriculture is able to produce more food per hectare, but increases the need for fresh water and chemicals for pesticides and fertilizer. Much of the rise in the food supply since 1950 has been due to greatly expanded irrigation and the use of pesticides and fertilizers. However, reservoirs will eventually silt up and aquifers (subsurface water supplies) will be depleted. Irrigation with surface or subsurface water can also cause salt to accumulate in the soil. As the irrigation water soaks into the soil and evaporates, it leaves the minerals behind. Eventually, these minerals, including sodium chloride and other salts can build up to the point that the soil is rendered unsuitable for growing anything. This has already happened in much of the central valley of California. In addition, the simple ecosystems used by modern industrial agriculture are much less resilient than the complex ecosystems they replace. High-yield crops in monocultures are more susceptible to insect infestations and disease than traditionally farmed crops. High-yield agricultural practices can also lead to soil erosion, and thus a further loss of topsoil.
Forests suffer similar pressures. Trees are harvested for timber and pulp. Land is cleared for agriculture. Mixed, old-growth forests are replaced with trees all of the same species planted at the same time. These forest monocultures suffer many of the same problems as food crop monocultures. They suffer from insect infestations and are much less stable than a diverse ecosystem. Grasslands have also been extensively modified and in many areas suffer desertification. As a consequence, there are significant losses of productivity in agricultural and forest lands from overcultivation, overgrazing, desertification, and deforestation around the world. The human population is expected to continue to grow rapidly during the twenty-first century. As it does, many of the environmental resources on which humans depend are being degraded.
According to one simple model developed by G. Tyler Miller in Living in the Environment, the total environmental degradation, or total environmental impact, of a population depends on three factors: (1) the number of people, (2) the average number of units (kilograms, liters or pounds, gallons) of resources used by each person, and (3) how each person uses those resources. According to this model, there are different ways over-population can cause the environment to become unable to support the rate of resource consumption.
In some regions of the world, people use a relatively small number of units of any given resource, but there are so many people that the resource is still depleted. This is called people overpopulation and it is the principal cause of environmental degradation in the world's poorer developing nations. Because the population is already consuming the minimum amount of resources possible to sustain life, reducing consumption is not possible. In order to prevent or limit resource depletion, some countries have instituted family planning or have strictly limited the number of children allowed in each family.
In other regions there are relatively few people, but each person uses (on the average) so many units of a resource that the resource still becomes depleted. Miller calls this consumption overpopulation. The United States has the highest level of consumption of any nation, although the level of resource consumption in many other nations is rapidly increasing. Reducing resource consumption is certainly possible, but is politically unpopular. Many economists connect the high standard of living in the United States to a high level of resource consumption, and possible reductions in standards of living are never popular.
There are several other factors related to environmental degradation. The first is population distribution. When large numbers of people are concentrated in a small area together with industrial activity, air and water pollution can rise to unacceptable levels. Other factors are wasteful patterns of consumption and overconsumption. When people consume more than they need to maintain a high standard of living or fail to effectively control waste through recycling and conservation, then environmental degradation can occur.
Another factor related to environmental degradation is carrying capacity, the maximum population of a given species that an ecosystem can support for an extended period of time. Every habitat, ecosystem, or biome has a carrying capacity for the best population level of any particular species. This is the level that maintains ecosystem diversity (including genetic diversity) without depleting ecosystem resources. Humans now inhabit every portion of Earth and occupy a variety of different ecosystems. Discussions of carrying capacity for human population must include the whole Earth as an ecosystem. There is much debate and discussion of Earth's carrying capacity. Many scientists feel that Earth is already overpopulated and that drastic measures must be taken immediately to reduce population and resource consumption. Others feel, just as strongly, that Earth can support far more people than it does now at a high standard of living. New technology, including extractive technologies and genetic engineering of food crops, will continue to increase Earth's carrying capacity.
A Global Issue
Environmental degradation affects everyone. International environmental concerns frequently focus on large-scale problems such as desertification or global warming. However, vulnerable groups, such as impoverished people living in marginal areas, are more concerned with local issues. They may worry about the loss of rangeland, soil erosion, or the need for more intensive farming. These and similar issues affect poor people because they are directly related to the household food supply and food security. Environmental degradation results in decreased production and lowered income. As the land is more intensively farmed, soil fertility decreases and crop yields are reduced. Unfortunately, rural poor people have few choices other than to overusing the limited resources available. The resulting environmental degradation can trigger a downward spiral in which the intensive use of resources results in more environmental degradation, which requires even more intensive use of resources.
see also Habitat Loss.
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Dregne, Howard E., and Adli Bishay. Desertification of Arid Land. Newark, NJ: Gordon & Breach Publishing Group, 1983.
Ehrlich, Paul R. The Population Bomb. New York: Ballantine Books, 1971.
Findley, Rowe. "Will We Save Our Own?" National Geographic 178, no. 3 (1990): 106-136.
Miller, G. Tyler, Jr. Living in the Environment, 6th ed. Belmont, CA: Wadsworth Publishing Company, 1990.
Odum, Eugene Pleasants. Fundamentals of Ecology, 3rd ed. Philadelphia: W. B. Saunders Company, 1971.
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Many of the resources to which humans have free access such as clean air, open oceans and the fishes in these oceans, wildlife, migratory birds, atmospheric gases, and stratospheric ozone are held in common. Everyone has the opportunity to use or even abuse these resources. Because it is each individual's self-interest to extract as much of a resource as possible, resources can easily be overharvested or converted to nonrenewable resources. This is often called the "tragedy of the commons," after the practice of grazing sheep or other animals on property held in common by the whole community. When there are relatively few users, the use of resources held in common has little effect. When there are many users, the cumulative effect of many people trying to maximize their use of the same resource can lead to degradation or destruction of the resource. Humans may be able to avoid the tragedy of the commons if they can convert their thinking from a self-centered viewpoint to a broader perspective.