In extreme cases, this latter has degraded aquatic ecosystems and rendered water supplies unpotable.

Other contaminants, derived from industrial chemicals, are also contributing to environmental change via air pollution and may also be threat to human health. Examples include chlorofluoro carbons (CFCs) that affect the ozone layer in the stratosphere.

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In order to meet the growing needs of human beings, energy consumption has increased markedly during the 20th century. Over the past 25 years global energy use has risen some 70 per cent and is expected to keep up climbing.

Today, carbon dioxide emissions from human sources—mostly from the burning of fossil fuels—averages more than 7 billion metric tonnes of carbon per year and have begun to alter the dynamics of the world’s climatic system (UNO, World Resources 1998-99: 171-72).

It may be seen from that in 1900 the world energy consumption was 1,000 millions of tonnes coal equivalents which got doubled in 1940, being 2,000 millions of tonnes.

In 1960, this figure rose to 4,000 millions of tonnes coal equivalents while in 1980 it went up to 9,000 millions of tonnes coal equivalents.

Motor vehicles have brought enormous social and economic benefits. But the widespread use of vehicles also has real environmental and economic costs, which have ballooned as vehicle numbers have raised sharply in the past few decades. Currently, the transport sector consumes about one half of the world’s oil production; the bulk of it is motor fuel.

The adoption of car as a common item in family life and commerce began after the Second World War in developing countries. In 1950, there were only 70 million cars, trucks, buses, on the world’s roads. By 1994, there was about nine times that number, or 630 million.

Since 1970, the global fleet has been growing at the rate of about 16 million vehicles per year. This expansion has been accompanied by a similar linear growth in fuel consumption.

If this kind of linear growth continues, by the year 2025 there will be over 1 billion vehicles on the world’s roads.

The growing use of internal combustion vehicles, especially in urban areas will increase congestion, raise the demand for oil, worsen air pollution, and increase emissions of a variety of green house gases, including methane, ozone, carbon monoxide, nitrous oxide and CO2.

Worldwide, motor vehicles currently emit well over 900 million metric tons of CO2 each year, leading to environmental pollution, acidifi­cation and ozone depletion (Ibid.).

Undoubtedly, carbon dioxide is the most abundant greenhouse gas, but the nitrous oxide, ozone and CFCs also absorb infrared radiation and it is well established that concentration of these gases has also increased due to human activity.

Welburn (1988) indicates that the current concen­tration of nitrous oxide is 0.30 ppm and predicts that by the year 2050 this will rise to 0.35 ppm due to the extensive use of nitrate fertilizers and the denitrifying effects of bacteria in the soil. Moreover, there is increasing concentration of methane in the atmosphere which has been reported by numerous workers.

The main sources of methane are bacterial decompo­sition of material in rubbish dumps and rice fields as well as gaseous emission from cattle, due to bacterial breakdown of cellulose in the animals’ guts, global wetlands and burning of vegetation.

One of the major sources of methane enrichment is biomass burning owing to the large-scale deforestation which is occurring in the tropical forests. Methane is an active heat trapper. It is expected that by 2030 A.D. the effect of methane on global warming will be just as significant as the extra carbon dioxide produced (Raynaud et al., 1988: 655-57).