the concept of heat as a pollutant may seem improbable on a cold winter day, at any time of year an increase in water temperature
has an effect on water life. Heat can be unnaturally added to streams and lakes in a number of ways. One is to cut down a
forest completely. The brooks and streams that flowed through it are then exposed to the sun. Their temperatures begin to
rise. As they flow into larger bodies of water, these in turn are warmed. This can kill fish and other water animals incapable
of tolerating the higher temperatures.
pollution is a consequence of the rising energy needs of man. As electric power plants burn fossil fuels or nuclear fuel to
provide this energy, they release considerable amounts of heat. Power plants are usually located near bodies of water, which
the plants use for heat-dissipation purposes. Some stretches of the Hudson River in New York no longer freeze in winter because of the flow of hot water into the river
from adjacent power plants. Living things--especially such cold-blooded animals as fish--are very sensitive to even small
changes in the average temperature. Because of the added heat in waters affected by power plants, many aquatic habitats may
be undergoing drastic change. In some instances, the warmer water may cause fish eggs to hatch before their natural food supply
is available. In other instances, it may prevent fish eggs from hatching
In addition, a very small rise in
the average temperature of the Earth's surface could produce profound climatic changes. Some experts believe that it would
cause the Greenland and Antarctic ice caps to melt, raising ocean levels and
inundating large areas of land.
worldwide temperatures can be affected when the products of combustion--carbon monoxide, water vapor, and carbon dioxide--are
emitted into the air, especially at high altitudes. Since the normal level of carbon dioxide in the air is quite small, any
significant addition is a potential threat. Although solar energy on its way to the Earth's surface easily passes through
layers of carbon dioxide, some of the heat escaping from the Earth would be absorbed by increased amounts of atmospheric carbon
dioxide, much as heat is trapped in a greenhouse. A worldwide greenhouse effect of this type might produce a dangerously warmer
world. Since the late 19th century, the average global temperature has increased between 0.3°C and 0.6°C. Internationally,
1990 was the hottest year on record since official weather records first started being kept by the British in about 1860.