Environment, the thin layer of life and life supports called the biosphere, including the earth's air, soil, water, and living organisms.

Constituents of the Environment

The atmosphere that shelters the earth from excessive amounts of ultraviolet radiation and enables life to exist is a gaseous mixture of nitrogen, oxygen, hydrogen, carbon dioxide, water vapour, other elements and compounds, and dust particles. Heated by the sun and by radiant energy from the earth, the atmosphere circulates about the planet and modifies temperature differences. Of the earth's water, 97 per cent makes up the oceans, 2 per cent is ice, and 1 per cent is the fresh water in rivers, lakes, groundwater, and atmospheric and soil moisture. The soil is the thin mantle of material that supports terrestrial life. It is the product of climate, parent material such as glacial till and sedimentary rocks, and vegetation. Dependent on all these are the earth's living organisms, including humans. Plants use water, carbon dioxide, and sunlight to convert raw materials into carbohydrates through photosynthesis; animal life, in turn, is dependent on plants, in a sequence of interconnected relationships known as the food web.
Throughout its long history, the earth has changed slowly. Continental drift (the result of Plate Tectonics) separated landmasses, oceans invaded and retreated from the land, and mountains rose and were worn down, depositing sediments along the edges of seas (See Geology). Climates warmed and cooled, and life forms appeared and disappeared as the environment changed. The most recent major environmental event in the earth's history occurred in the Quaternary period, during the Pleistocene epoch (between 2.5 million and 10,000 years ago), also known as the Ice Age. The subtropical climate was destroyed and the face of the northern hemisphere was reshaped. Ice sheets advanced and retreated four times in North America and three times in Europe, swinging the climate between cold and temperate, influencing vegetation and animal life, and ultimately forming the environment as it exists today. The epoch following the Pleistocene is known variously as the Recent, the Postglacial epoch, and the Holocene. During this time the environment of the earth has remained more or less stable.

Environmental Problems

The species Homo sapiensюthat is, humansюappeared late in the earth's history, but was ultimately able to modify the earth's environment by its activities. Although humans apparently first appeared in Africa, they quickly spread throughout the world. Because of their unique mental and physical capabilities, humans were able to escape the environmental constraints that limited other species and to change the environment to meet their needs. Although early humans undoubtedly lived in some harmony with the environment, as did other animals, their retreat from the wilderness began with the first, prehistoric agricultural revolution. The ability to control and use fire allowed them to modify or eliminate natural vegetation, and the domestication and herding of grazing animals resulted in overgrazing and soil erosion. The domestication of plants also led to the destruction of natural vegetation to make room for crops, and the demand for wood for fuel denuded mountains and depleted forests. Wild animals were slaughtered for food and destroyed as pests and predators.
While human populations remained small and human technology modest, their impact on the environment was localized. As populations increased and technology improved and expanded, however, more significant and widespread problems arose. Rapid technological advances after the Middle Ages culminated in the Industrial Revolution, which involved the discovery, use, and exploitation of fossil fuels, as well as the extensive exploitation of the earth's mineral resources. With the Industrial Revolution, humans began in earnest to change the face of the earth, the nature of its atmosphere, and the quality of its water. Today, unprecedented demands on the environment from a rapidly expanding human population and from advancing technology are causing a continuing and accelerating decline in the quality of the environment and its ability to sustain life.

Carbon Dioxide

One impact that the burning of fossil fuels has had on the earth's environment has been the increase of carbon dioxide (CO2) in the earth's atmosphere. The amount of atmospheric CO2 apparently remained stable for centuries, at about 260 ppm (parts per million), but over the past 100 years it has increased to 350 ppm. The significance of this change is its potential for raising the temperature of the earth through the process known as the greenhouse effect. Carbon dioxide in the atmosphere tends to prevent the escape of outgoing long-wave radiation from the earth to outer space; as more heat is produced and less escapes, the temperature of the earth increases.
A significant global warming of the atmosphere would have profound environmental effects. It would speed the melting of polar ice caps, raise sea levels, change the climate regionally and globally, alter natural vegetation, and affect crop production. These changes would, in turn, have an enormous impact on human civilization. Since 1850 there has been a mean rise in global temperature of about 1ђ C (1.8ђ F). Some scientists have predicted that rising levels of CO2 and other "greenhouse gases" will cause temperatures to continue to increase, with estimates ranging from 2ђ to 6ђ C (4ђ to 11ђ F) by the middle of the 21st century. However, other scientists who research climate effects and trends dispute the theories of global warming, and attribute the most recent rise to normal temperature fluctuations.

Acid Deposition

Also associated with the burning of fossil fuels is acid deposition, which is caused by the emission of sulphur dioxide and nitrous oxides into the air from power plants and motor vehicles. These chemicals interact with sunlight, moisture, and oxidants to produce sulphuric and nitric acids, which are carried with the atmospheric circulation and come to earth in rainfall and snowfall, commonly referred to as acid rain, and as dry deposits in the form of dry particles and atmospheric gases.

Acid rain is a major global problem. The acidity of some precipitation in northern North America and Europe is equivalent to that of vinegar. Acid rain corrodes metals, weathers stone buildings and monuments, injures and kills vegetation, and acidifies lakes, streams, and soils, especially in the poorly buffered regions of north-eastern North America and northern Europe. In these regions, lake acidification has killed some fish populations. It is also now a problem in the south-eastern United States and in central North Africa. Acid rain can also slow forest growth; it is associated with forest decline at high elevations in both North America and Europe.

Ozone Destruction

In the 1970s and 1980s, scientists began to find that human activity was having a detrimental effect on the global ozone layer, a region of the atmosphere that shields the earth from the sun's harmful ultraviolet rays. Without this gaseous layer, which is found at about 40 km (25 mi) above sea level, no life could survive on the planet. Studies showed the ozone layer was being damaged by the increasing use of industrial chemicals called chlorofluorocarbons (CFCs, compounds of fluorine) which are used in refrigeration, air conditioning, cleaning solvents, packing materials, and aerosol sprays. Chlorine, a chemical by-product of CFCs, attacks ozone, which consists of three molecules of oxygen, by taking one molecule away to form chlorine monoxide. Chlorine monoxide then reacts with oxygen atoms to form oxygen molecules, releasing chlorine molecules that break up other molecules of ozone.
It was initially thought that the ozone layer was being reduced gradually all over the globe. In 1985, however, further research revealed a growing ozone hole concentrated above Antarctica; 50 per cent or more of the ozone above this area of the earth was being depleted seasonally (beginning each October). A thinning of the ozone layer exposes life on earth to excessive ultraviolet radiation, which can increase skin cancer and cataracts, reduce immune system responses, interfere with the photosynthetic process of plants, and affect the growth of oceanic phytoplankton. Because of the growing threat of these dangerous environmental effects, many nations are working towards eliminating the manufacture and use of CFCs at least by the year 2000. However, CFCs can remain in the atmosphere for more than 100 years, so ozone destruction will continue to pose a threat for decades to come.

Chlorinated Hydrocarbons

Extensive use of synthetic pesticides derived from chlorinated hydrocarbons in pest control has had disastrous environmental side effects. These organochlorine pesticides are highly persistent and resist biological degradation. Relatively insoluble in water, they cling to plant tissues and accumulate in soils, the bottom mud of streams and ponds, and the atmosphere. Once volatilized, the pesticides are distributed worldwide, contaminating wilderness areas far removed from agricultural regions, and even the Antarctic and Arctic zones.
Although these synthetic chemicals are not found in nature, they nevertheless enter the food chain. The pesticides are either taken in by plant eaters or absorbed directly through the skin by such aquatic organisms as fish and various invertebrates. The pesticide is further concentrated as it passes from herbivores (plant eaters) to carnivores (meat eaters). It becomes highly concentrated in the tissues of animals at the end of the food chain, such as the peregrine falcon, bald eagle, and osprey. Chlorinated hydrocarbons interfere in the calcium metabolism of birds, causing thinning of egg shells and subsequent reproductive failure. As a result, some large predatory and fish-eating birds have been brought close to extinction. Because of the dangers of pesticides to wildlife and to humans, and because insects have acquired resistance to them, the use of halogenated hydrocarbons such as DDT is declining rapidly in the Western world, although large quantities are still used in developing countries. In the early 1980s, the halogenated pesticide EDB, or Ethylene Dibromide, also aroused great concern as a potential carcinogen, and was eventually banned. Closely related to DDT is another group of compounds: the polychlorinated biphenyls, or PCBs. For years these compounds have been used in industrial production, and eventually they found their way into the environment. Their impact on humans and wildlife has been similar to that of pesticides. Because of their extreme toxicity, the use of PCBs is now restricted to insulators in electrical transformers and capacitors. PCDD is the most toxic of another related group of highly toxic compounds, the dioxins, or polychlorinated dibenzo-para-dioxins. The extent of toxicity of these carcinogenic compounds in humans has not yet been proved. PCDD may be found as an impurity in wood and paper preservatives and in herbicides. Agent Orange, a defoliant widely used in jungle warfare, contains minute traces of dioxin.

Other Toxic Substances

Toxic substances are chemicals and mixtures of chemicals whose manufacturing, processing, distribution, use, and disposal present an unreasonable risk to human health and the environment. Most of these toxic substances are synthetic chemicals that enter the environment and persist there for long periods of time. Major concentrations of toxic substances occur in chemical dump sites. If they seep into soil and water, the chemicals can contaminate water supplies, air, crops, and domestic animals, and have been associated with human birth defects, miscarriages, and organic diseases. Despite known dangers, the problem is not lessening. In a recent 15-year period, more than 4 million new synthetic chemicals were manufactured, and new ones are being created at the rate of 500 to 1,000 each year.

Radiation

Although atmospheric testing of nuclear weapons has been banned by most countries, eliminating a large source of radioactive fallout, nuclear radiation still remains an environmental problem. Power plants always release some amount of radioactive waste into the air and water, but the main danger is the possibility of nuclear accidents, in which massive amounts of radiation are released into the environmentюas happened at Chernobyl', Ukraine, in 1986. In fact, since the breakup of the Union of Soviet Socialist Republics (USSR), the world has learned that contamination of that region from nuclear accidents and nuclear wastes is far more extensive than had been realized. A greater problem facing the nuclear industry is the storage of nuclear wastes, which remain toxic for 700 to 1 million years, depending on the type. Safe storage for geological periods of time is problematic; meanwhile nuclear wastes accumulate, threatening the integrity of the environment.

Loss of Wild Lands

Increasing numbers of humans are encroaching on remaining wild landsю even in those areas once considered relatively safe from exploitation. Insatiable demands for energy are forcing the development of Arctic regions for oil and gas and threatening the delicate ecological balance of tundra ecosystems and their wildlife. Tropical forests, especially in South-East Asia and the Amazon River Basin, are being destroyed at an alarming rate for timber, conversion to crop and grazing lands, pine plantations, and settlements. It was estimated at one point in the 1980s that such forest lands were being cleared at the rate of 20 hectares (nearly 50 acres) a minute; another estimate put the rate at more than 200,000 sq km (78,000 sq mi) a year. In 1993, satellite data provided a rate of about 15,000 sq km (5,800 sq mi) a year in the Amazon Basin area alone. This tropical deforestation could result in the extinction of as many as 750,000 species, which would mean the loss of a multiplicity of products: food, fibres, medical drugs, dyes, gums, and resins. In addition, the expansion of croplands and grazing areas for domestic livestock in Africa, and illegal trade in endangered species and wildlife products, could mean the end of Africa's large mammals. In North America, logging of old-growth forests in the Pacific Northwest, surface mining, and encroaching urban and recreational development threaten the future of wilderness areas.

Soil Erosion

Soil erosion is accelerating on every continent and is degrading one-fifth to one-third of the cropland of the world, posing a significant threat to the food supply. For example, erosion is undermining the productivity of approximately 34 per cent of all cropland in the United States. In the Third World, increasing needs for food and firewood have resulted in the deforestation and cultivation of steep slopes, causing severe erosion. Adding to the problem is the loss of prime cropland to industry, dams, urban sprawl, and highways; the United States alone has lost 1.1 million hectares (2.7 million acres) of farmland to nonfarm uses. Soil erosion and the loss of cropland and forests also reduce the moisture- holding capacity of soils and add sediments to streams, lakes, and reservoirs.

Demands on Water and Air

The erosion problems described above are aggravating a growing world water problem. Most water problems are in the semiarid and coastal regions of the world. Expanding human populations need irrigation systems and water for industry; this is so depleting underground aquifers that salt water is intruding into them along coastal areas of the United States, Israel, Syria, and the Arabian Gulf states. In inland areas, porous rocks and sediments are compacting when drained of water, causing surface subsidence problems; this subsidence is already a serious problem in Texas, Florida, and California.
The world is also experiencing a steady decline in water quality and availability. About 75 per cent of the world's rural population and 20 per cent of its urban population have no ready access to uncontaminated water. In many regions, water supplies are contaminated with toxic chemicals and nitrates. Waterborne disease debilitates one-third of humanity and kills 10 million people a year.
During the 1980s and early 1990s, some industrialized countries improved air quality by reducing particulate matter and toxic chemicals, such as lead, but emissions of sulphur dioxide and nitrous oxides, the precursors of acid deposition, still remain. Massive air pollution occurs over much of Eastern Europe and the former USSR.

The Earth Summit

In June 1992, the United Nations Conference on Environment and Development, commonly known as the Earth Summit, convened for 12 days on the outskirts of Rio de Janeiro, Brazil. The Earth Summit developed and legitimized a broad agenda for environmental, economic, and political change. The purposes of the conference were to identify long-term environmental reforms and to initiate processes for their international implementation and supervision. Conventions were held to discuss and adopt documents on the environment. The major topics covered by these conventions included climate change, biodiversity, forest protection, Agenda 21 (a 900-page blueprint for environmental development), and the Rio Declaration (a six-page statement that called for integrating the environment with economic development). The Earth Summit was an historic event of great significance. Not only did it make the environment a priority on the world's agenda, but delegates from 178 countries attended, making it the largest conference ever held.

Outlook

The environmental outlook for the future is mixed. In spite of economic and political changes, interest in and concern about the environment remains high. Air quality has improved, but problems of acid deposition, chlorofluorocarbons and ozone depletion, and heavy air pollution in Eastern Europe still seek solutions and concerted action. Until acid deposition is diminished, loss of aquatic life in northern lakes and streams will continue, and forest growth may be affected. Water pollution will remain a growing problem as increasing human populations put additional stress on the environment. Infiltration of toxic wastes into underground aquifers and intrusion of saline waters into coastal freshwater aquifers have not been stopped.
Depletion of aquifers in many parts of the world and growing demand for water will bring agricultural, industrial, and urban use of water into conflict. This shortage will force water usage restrictions and will increase the cost of water consumption. Water could become the "energy crisis" of the early 2000s. Pollution of coastal and fresh water along with overharvesting has so depleted fishery resources that five to ten years of little or no fishing will be required for stocks to recover. Without concerted efforts to save habitats and reduce poaching and the illegal worldwide wildlife trade, many wildlife species will become extinct. In spite of our knowledge of how to reduce soil erosion, it continues to be a worldwide problem, largely because too many agriculturalists and developers show little interest in controlling it. Finally, the destruction of wild lands, in both temperate and tropical regions, could result in massive extinctions of animal and plant life.
To reduce environmental degradation and for humanity to save its habitat, societies must recognize that the environment is finite. Environmentalists believe that, as populations and their demands increase, the idea of continuous growth must give way to a more rational use of the environment, but that this can be accomplished only by a dramatic change in the attitude of the human species. The human attack on the environment has been compared to the dramatic upheavals of the earth in the geological past; whatever a society's attitude may be towards continuous growth, humanity should recognize that this attack threatens human survival.
Acid Rain, form of air pollution, currently a subject of great controversy because of the widespread environmental damage for which it has been blamed. It forms when oxides of sulphur and nitrogen combine with atmospheric moisture to yield sulphuric and nitric acids, which may then be carried long distances from their source before they are deposited by rain. The pollution may also take the form of snow or fog or be precipitated in dry forms. In fact, although the term "acid rain" has been in use for more than a centuryюit is derived from atmospheric studies that were made in the region of Manchester, Englandюthe more accurate scientific term would be "acid deposition". The dry form of such precipitation is just as damaging to the environment as the liquid form.
The problem of acid rain originated with the Industrial Revolution, and it has been growing ever since. The severity of its effects has long been recognized in local settings, as exemplified by the periods of acid smog in heavily industrialized areas. The widespread destructiveness of acid rain, however, has become evident only in recent decades. One large area that has been studied extensively is northern Europe, where acid rain has eroded structures, injured crops and forests, and threatened or depleted life in freshwater lakes. In 1984, for example, environmental reports indicated that almost half of the trees in Germany's Black Forest had been damaged by acid rain. The north-eastern United States and eastern Canada have also been particularly affected by this form of pollution; damage has also been detected in other areas of these countries and other regions of the world.
Industrial emissions have been blamed as the major cause of acid rain. Because the chemical reactions involved in the production of acid rain in the atmosphere are complex and as yet little understood, industries have tended to challenge such assessments and to stress the need for further studies; and because of the cost of pollution reduction, governments have tended to support this attitude. Studies released by the US government in the early 1980s, however, strongly implicated industries as the main source of acid rain, in the eastern United States and Canada. In 1988, as part of the United Nations Convention on Long-Range Transboundary Air Pollution Agreement (1979), 25 nations ratified a protocol freezing the rate of nitrogen oxides emissions at 1987 levels. The 1990 amendments to the US Clean Air Act of 1967 put in place regulations to reduce the release of sulphur dioxide from power plants to 10 million tons per year by January 1, 2000. This amount is about half of the emissions of 1990.
In Europe, the 1979 Convention is administered through the United Nations Economic Commission for Europe. The UNECE produced the first Sulphur Protocol (1985) which called for a reduction of sulphur emissions to 70 per cent of 1980 levels by 1993 (the United Kingdom did not sign this protocol, but nevertheless achieved the reduction); the Nitrogen Oxides protocol (as detailed above); the Volatile Organic Compounds Protocol (1991), calling for a reduction in emissions to 70 per cent of 1988 levels by 1999; and the second Sulphur Protocol (1994), by which sulphur emissions are to be reduced in intermediate stages to a goal of 20 per cent of 1980 levels by 2010юall of which the United Kingdom did sign. In addition, catalytic converters, which reduce the emission of nitrogen oxides, have been compulsory on all new cars in the United Kingdom since 1993.

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