energy, sources of:

Environmental Considerations

The demand for energy has increased steadily through much of the late 20th and early 21st cent., not only because of the growing population but also because of the greater number of technological goods available and the increased affluence that has brought these goods within the reach of a larger proportion of the population. For example, despite the introduction of more fuel-efficient motor vehicles (average miles per gallon increased by 34% between 1975 and 1990), the consumption of fuel by vehicles in America increased by 20% between 1975 and 1990. The rise in gasoline consumption is attributable to an increase in the number of miles the average vehicle traveled and to a 40% increase in the same period in the number of vehicles on the road. From 1990 to the mid-2000s, the average fuel efficiency decreased (a trend that had begun in the 1980s), due in part to the increasing use of light trucks as passenger vehicles, but it subsequently began to improve due to increasingly stringent federal standards. The number of miles traveled increased more slowly during the same period, and the total amount of fuel consumed declined for a time due to recession and then increased to around the levels of the mid-2000s.

As a result of the increase in the consumption of energy, concern has risen about the depletion of natural resources, both those used directly to produce energy and those damaged during the exploitation of the fuels or as a result of contamination by energy waste products (see under conservation of natural resources). Most of the energy consumed is ultimately generated by the combustion of fossil fuels, such as coal, petroleum, and natural gas. Although the world has only a finite supply of these fuels, and concern was long focused on decreasing supply, the environmental damage caused by the use of such fuels, especially coal, is a greater concern. The production and combustion of these fuels releases various pollutants (see pollution), such as soot, carbon monoxide and sulfur dioxide, which pose health risks and contribute to acid rain, and carbon dioxide and methane, which contribute to global warming. There are also destructive effects to sensitive wildlands (e.g., the tropical rain forests, the arctic tundra, and coastal marshes) during the exploitation of their resources.

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