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Referat :: POLLUTION
POLLUTION, ENVIRONMENTAL. Efforts to improve the standard of living for humans--through the control of nature and the development of new products--have also resulted in the pollution, or contamination, of the environment. Much of the world's air, water, and land is now partially poisoned by chemical wastes. Some places have become uninhabitable. This pollution exposes people all around the globe to new risks from disease. Many species of plants and animals have become endangered or are now extinct. As a result of these developments, governments have passed laws to limit or reverse the threat of environmental pollution.
All living things exert some pressure on the environment. Predatory animals, for example, reduce the population of their prey, and animal herds may trample vast stretches of prairie or tundra. The weather could be said to cause pollution when a hurricane deposits tons of silt from flooded rivers into an estuary or bay. These are temporary dislocations that nature balances and accommodates to. Modern economic development, however, sometimes disrupts nature's delicate balance. The extent of environmental pollution caused by humans is already so great that some scientists question whether the Earth can continue to support life unless immediate corrective action is taken.
Ecology and Environmental Deterioration
The branch of science that deals with how living things, including humans, are related to their surroundings is called ecology (see Ecology). The Earth supports some 5 million species of plants, animals, and microorganisms. These interact and influence their surroundings, forming a vast network of interrelated environmental systems called ecosystems. The arctic tundra is an ecosystem and so is a Brazilian rain forest. The islands of Hawaii are a relatively isolated ecosystem. If left undisturbed, natural environmental systems tend to achieve balance or stability among the various species of plants and animals. Complex ecosystems are able to compensate for changes caused by weather or intrusions from migrating animals and are therefore usually said to be more stable than simple ecosystems. A field of corn has only one dominant species, the corn plant, and is a very simple ecosystem. It is easily destroyed by drought, insects, disease, or overuse. A forest may remain relatively unchanged by weather that would destroy a nearby field of corn, because the forest is characterized by greater diversity of plants and animals. Its complexity gives it stability.
Every environmental system has a carrying capacity for an optimum, or most desirable, population of any particular species within it. Sudden changes in the relative population of a particular species can begin a kind of chain reaction among other elements of the ecosystem. For example, eliminating a species of insect by using massive quantities of a chemical pesticide also may eliminate a bird species that depends upon the insect as a source of food.
Such human activities have caused the extinction of a number of plant and animal species. For example, overhunting caused the extinction of the passenger pigeon (see Endangered Species; Pigeon and Dove). The last known survivor of the species died at the Cincinnati Zoo in 1914. Less than a century earlier, the passenger pigeon population had totaled at least 3 billion. Excessive hunting or infringement upon natural habitats is endangering many other species. The great whales and the California condor are among the endangered. (See also Conservation, " Wildlife Conservation. ")
Population Growth and Environmental Abuse
The reduction of the Earth's resources has been closely linked to the rise in human population. For many thousands of years people lived in relative harmony with their surroundings. Population sizes were small, and life-supporting tools were simple. Most of the energy needed for work was provided by the worker and animals. Since about 1650, however, the human population has increased dramatically. The problems of overcrowding multiply as an ever-increasing number of people are added to the world's population each year.
The rate of growth of the world's population has finally begun to slow, after reaching an all-time high of about 2 percent in 1970. In 1987 there were 5 billion people on the planet. The United Nations predicts the population growth rate will decline to 1. 5 percent by the year 2000. Even so, there will be 6. 1 billion people living on Earth at the beginning of the 21st century--twice the number of people living on Earth in 1960. (See also Population.)
The booming human population is concentrated more and more in large urban areas. Many cities now have millions of inhabitants. In less developed countries of Asia, Africa, and Latin America, many of these cities are overpopulated because of an influx of people who have left rural homes in search of food, shelter, and employment. Some ...
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