Humans and the Environment.

Humans and the environment

Humans and the Environment

1 - Air Pollution:

A) This is the contamination of the atmosphere by gaseous, liquid, or solid wastes or by-products that can endanger human health and the health and welfare of plants and animals, or can attack materials, reduce visibility, or produce undesirable odours. Among air pollutants emitted by natural sources, only the radioactive gas radon is recognised as a major health threat. A by-product of the radioactive decay of uranium minerals in certain kinds of rock, radon seeps into the basements of homes built on these rocks, posing a risk of lung cancer to residents.

Each year industrially developed countries generate billions of tons of pollutants. The most prevalent and widely dispersed air pollutants are described in the accompanying table. The level is usually given in terms of atmospheric concentrations (micrograms of pollutants per cubic metre of air) or, for gases, in terms of parts per million, that is, number of pollutant molecules per million air molecules. Many come from directly identifiable sources; sulphur dioxide, for example, comes from electric power plants burning coal or oil. Others are formed through the action of sunlight on previously emitted reactive materials (called precursors). For example, ozone, a dangerous pollutant in smog, is produced by the interaction of hydrocarbons and nitrogen oxides under the influence of sunlight. Ozone has also caused serious crop damage. On the other hand, the discovery in the 1980s that air pollutants such as fluorocarbons are causing a loss of ozone from the earth's protective ozone layer has caused the phasing out of these materials.

Meteorology and Health Effects

Pollutant concentration is reduced by atmospheric mixing, which depends on such weather conditions as temperature, wind speed, and the movement of high and low pressure systems and their interaction with the local topography, for example, mountains and valleys. Normally, temperature decreases with altitude. But when a colder layer of air settles under a warm layer, producing a temperature or thermal inversion, atmospheric mixing is retarded and pollutants may accumulate near the ground. Inversions can become sustained under a stationary high-pressure system coupled with low wind speeds.

Periods of only three days of poor atmospheric mixing can lead to high concentrations of hazardous materials in high-pollution areas and, under severe conditions, can result in injury and even death. An inversion over Donora, Pennsylvania, in 1948 caused respiratory illness in over 6,000 people and led to the death of 20. Severe pollution in London took 3,500 to 4,000 lives in 1952 and another 700 in 1962. Release of methyl isocyanate into the air during a temperature inversion caused the disaster at Bhopal, India, in December 1984, with at least 3,300 deaths and more than 20,000 illnesses. The effects of long-term exposure to low concentrations are not well defined; however, those most at risk are the very young, the elderly, smokers, workers whose jobs expose them to toxic materials, and people with heart or lung disease. Other adverse effects of air pollution are potential injury to livestock and crops.

Often, the first noticeable effects of pollution are aesthetic and may not necessarily be dangerous. These include visibility reduction due to tiny particles suspended in air, or bad odours, such as the rotten egg smell produced by hydrogen sulphide emanating from pulp and paper mills.

Sources and Control

The combustion of coal, oil, and petrol accounts for much of the airborne pollutants. More than 80 per cent of the sulphur dioxide, 50 per cent of the nitrogen oxides, and 30 to 40 per cent of the particulate matter emitted to the atmosphere in the United States are produced by fossil-fuel-fired electric power plants, industrial boilers, and residential furnaces. Eighty per cent of the carbon monoxide and 40 per cent of the nitrogen oxides and hydrocarbons come from burning petrol and diesel in cars and lorries. Other major pollution sources include iron and steel mills; zinc, lead, and copper smelters; municipal incinerators; oil refineries; cement plants; and nitric and sulphuric acid plants.

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Potential pollutants may exist in the materials entering a chemical or combustion process (such as lead in petrol), or they may be produced as a result of the process itself. Carbon monoxide, for example, is a typical product of internal-combustion engines. Methods for controlling air pollution include removing the hazardous material before it is used, removing the pollutant after it is formed, or altering the process so that the pollutant is not formed or occurs only at very low levels. Car exhaust pollutants can be controlled by burning the fuel as completely as possible, by recirculating fumes from fuel tank, carburettor, and crankcase, and by changing the engine exhaust to harmless substances in catalytic converters. Industrially emitted particulates may be trapped in cyclones, electrostatic precipitators, and filters. Pollutant gases can be collected in liquids or on solids, or incinerated into harmless substances.

Large-Scale Effects

The tall smokestacks used by industries and utilities do not remove pollutants but simply boost them higher into the atmosphere, thereby reducing their concentration at the site. These pollutants may then be transported over large distances and produce adverse effects in areas far from the site of the original emission. Sulphur dioxide and nitrogen oxide emissions from Britain are causing acid rain in Norway and Sweden. The pH level, or relative acidity, of many freshwater lakes has been altered so dramatically by acid rain that entire fish populations have been destroyed. Sulphur dioxide emissions and the subsequent formation of sulphuric acid can also be responsible for the attack on limestone and marble at large distances from the source.

The world-wide increase in the burning of coal and oil since the late 1940s has led to ever increasing concentrations of carbon dioxide. The resulting "greenhouse effect", which allows solar energy to enter the atmosphere but reduces the reemission of infrared radiation from the earth, could conceivably lead to a warming trend that might affect the global climate and lead to a partial melting of the polar ice caps. Possibly an increase in cloud cover or absorption of excess carbon dioxide by the oceans (in the so-called carbon cycle) would check the greenhouse effect before it reached the stage of polar melting. Nevertheless, many research reports released during the 1980s have indicated that the greenhouse effect is definitely under way and that the nations of the world should be taking immediate steps to deal with it.

Action by Governments

Various countries have set standards in legislation in the form of concentration levels that are believed to be low enough to protect public health. Source emission standards are also specified to limit the discharge of pollutants into the air so that air-quality standards will be achieved. However, the nature of the problem requires the implementation of international environmental treaties, and to this end 49 countries agreed in March 1985 on a United Nations convention to protect the ozone layer. This "Montreal Protocol", which was renegotiated in 1990, called for the phase-out of certain chlorocarbons and fluorocarbons by the end of the century and provides aid to developing countries in making this transition. In addition, several international protocols have been aimed specifically at reducing the incidence of acid rain.

The Greenhouse Effect

This is the term for the role the atmosphere plays in helping warm the earth's surface. The atmosphere is largely transparent to incoming short-wave solar radiation, which is absorbed by the earth's surface. Much of this radiation is then re-emitted at infrared wavelengths, but it is reflected back by gases such as carbon dioxide, methane, nitrous oxide, halocarbons, and ozone in the atmosphere. This heating effect is at the root of the theories concerning global warming.

The amount of carbon dioxide in the atmosphere has been increasing by 0.4 per cent a year because of the use of fossil fuels such as oil, gas, and coal; the slash-and-burn clearing of tropical forests has also been a contributing factor in the carbon cycle. Other gases that contribute to the greenhouse effect, such as methane and chlorofluorocarbons, are increasing even faster. The net effect of these increases could be a world-wide rise in temperature, estimated at 2? to 6? C (4? to 11? F) over the next 100 years. Warming of this magnitude would alter climates throughout the world, affect crop production, and cause sea levels to rise significantly. If this happened, millions of people would be adversely affected by major flooding.

Global Warming

Global Warming is an increase in the earth's temperature due to the use of fossil fuels and other industrial processes leading to a build-up of "greenhouse gases" (carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons) in the atmosphere. It has been known since 1896 that carbon dioxide helps stop the sun's infrared radiation from escaping into space and thus functions to maintain the earth's relatively warm temperature (this is called the greenhouse effect). The question is whether the measurably increasing levels of carbon dioxide in the atmosphere over the last century will lead to elevated global temperatures, which could result in coastal flooding (through a rise in sea level) and major climatic changes, and have serious implications for agricultural productivity.

Since 1850 there has been a mean rise in global temperature of approximately 1? C (1.8? F), but this rise could just be part of a natural fluctuation. Such fluctuations have been recorded for tens of thousands of years and operate in short-term as well as long-term cycles. The difficulty of distinguishing human-made causes of carbon dioxide emissions from natural sources is one reason why governmental legislation regarding their control has been slow in coming. However, the potential consequences of global warming are so from essaybank.co.uk great that many of the world's top scientists have urged immediate action, and have called for international co-operation on the problem.

B) The Ozone Layer

This is, in nature, a region of the atmosphere from 19 to 48 km above the earth's surface. Ozone concentrations of as much as 10 parts per million occur in the ozone layer. The ozone forms there by the action of sunlight on oxygen. This action has been taking place for many millions of years, but naturally occurring nitrogen compounds in the atmosphere apparently have kept the ozone concentration at a fairly stable level. Concentrations this great at ground level are dangerous to human health; but because the ozone layer protects life on earth from the full force of the sun's cancer-causing ultraviolet radiation, it is critically important. Therefore, scientists were concerned when they discovered, in the 1970s, that certain chemicals called chlorofluorocarbons, or CFCs (compounds of fluorine) - long used as refrigerants and in aerosol spray cans-posed a possible threat to the ozone layer. Released into the atmosphere, the chlorine-containing chemicals rise and are broken down by sunlight, whereupon the chlorine reacts with and destroys ozone molecules. For this reason, the use of CFCs in aerosols has been banned in many countries. Other chemicals, such as bromine halocarbons, and nitrous oxides from fertilisers, may also attack the ozone layer.

For several years, beginning in the late 1970s, research scientists working in Antarctica detected a periodic loss of ozone in the atmosphere high above that continent. The so-called ozone "hole" develops in the Antarctic spring and continues for several months before closing up again. Other studies, conducted using high-altitude balloons and weather satellites, indicated that the overall percentage of ozone in the Antarctic ozone layer is declining. Flights over the Arctic regions found a similar problem developing there. In 1985, a United Nations convention known as the "Montreal Protocol", signed by 49 countries, stated the intention of phasing out CFCs by the end of the century. In 1987, a treaty for the protection of the ozone layer was signed and later ratified by 36 nations. A total ban on the use of CFCs during the 1990s was proposed by the European Community (now the European Union) in 1989, and endorsed by United States President George Bush. In order to monitor ozone depletion on a global level, in 1991 NASA launched the 7-ton Upper Atmosphere Research Satellite. Orbiting earth at an altitude of 600 km, the spacecraft measures ozone variations at different altitudes, and is providing the first complete picture of upper atmosphere chemistry.

Chlorofluorocarbons

Fluorine compounds have many applications. The chlorofluorocarbons, odourless and non-poisonous liquids or gases such as freon, are used as a dispersing agent in aerosol sprays and as a refrigerant. In 1974, however, some scientists suggested that these chemicals reached the stratosphere and were destroying the earth's ozone layer. With confirmation of these findings by the late 1980s, the production of these chemicals began to be phased out.

Chlorofluorocarbons and human health

Fluorine and many fluorides, such as hydrogen fluoride and sodium fluoride, are extremely poisonous. Drinking water containing excessive amounts of fluorides causes tooth enamel to become brittle and to chip off, leaving a stained or mottled effect. The proper proportion of fluorides in drinking water, however, has been found to greatly reduce tooth decay.

Hydrocarbon Pollution from Vehicle Exhaust

Vehicle exhaust contains a number of airborne pollutants that adversely affect the health of animals and plants and the chemical nature of the atmosphere. Carbon dioxide and hydrocarbon emissions, two of the major components of vehicle exhaust, contribute significantly to global warming and are produced as a by-product of the combustion of petroleum-based fuels. Elevated carbon dioxide and hydrocarbon levels cause sunlight to be reflected and trapped within the atmosphere, which slowly raises the temperature of the atmosphere.

Air Pollution and Acid Rain

Rainwater was once the purest form of water available but now is often contaminated by pollutants in the air. Acid rain is caused when industrial emissions mix with atmospheric moisture. Pollutants may be carried in clouds for long distances before falling, which means that forests and lakes far away from factories may be damaged by acid rain. In the near vicinity of the factories, additional damage is caused by the deposition of larger pollutant particles falling to the ground in dry form. Air pollution has been increasing since the Industrial Revolution but only recently have side effects such as acid rain become severe and widespread enough to evoke international concern.

Acid Rain

Acid rain is a 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 century-it is derived from atmospheric studies that were made in the region of Manchester, England-the 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 recognised in local settings, as exemplified by the periods of acid smog in heavily industrialised 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 Trans-boundary 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 2010-all 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.

2 - Deforestation:

Deforestation is the large-scale removal of forest, prior to its replacement by other land uses. It is proceeding at about 17 million hectares each year .Between 1980 and 1990, annual deforestation rates were 1.2 per cent in Asia and the Pacific, 0.8 per cent in Latin America, and 0.7 per cent in Africa. Forest area is generally stable in Europe and North America, although the rate of transition from old-growth forest to other forms in North America is controversially high.

Deforestation may be distinguished from forest degradation, which is a reduction in forest quality. The two are linked, and result in several problems. They cause soil erosion and watershed destabilisation, resulting in flooding or drought. They reduce bio-diversity (the range of habitat, species, and genetic types), particularly significant in tropical forests which are home to much of the world's bio-diversity. The culture and knowledge of many forest peoples have evolved through centuries of nurturing the forest; they are diminishing as forest area reduces, as access to forest is increasingly restricted, and as traditional rights are eroded by governments. Deforestation affects the livelihoods of between 200 and 500 million people who depend on forests for their food, shelter, and fuel. Deforestation and degradation may contribute to regional and global climate imbalances. Forests play a major role in carbon storage; with their removal, excessive carbon dioxide in the atmosphere may lead to global warming, with many problematic side-effects.

While deforestation is now viewed as a problem, historically it was considered to assist national development. Natural forest "capital" was liquidated and replaced by other forms of capital, to produce food, raw materials, energy, or infrastructure.