Global Warming
The greenhouse effect, in environmental science, is a popular term for the effect that
certain variable constituents of the Earth's lower atmosphere have on surface
temperatures. It has been known since 1896 that Earth has been warmed by a blanket of
gasses (This is called the "greenhouse effect."). The gases--water vapor (H2O), carbon
dioxide (CO2), and methane (CH4)--keep ground temperatures at a global average of about
15 degrees C (60 degrees F). Without them the average would be below the freezing point
of water. The gases have this effect because as incoming solar radiation strikes the
surface, the surface gives off infrared radiation, or heat, that the gases trap and keep
near ground level. The effect is comparable to the way in which a greenhouse traps heat,
hence the term. Environmental scientists are concerned that changes in the variable
contents of the atmosphere--particularly changes caused by human activities--could cause
the Earth's surface to warm up to a dangerous degree. Since 1850 there has been a mean
rise in global temperature of approximately 1? C (approximately 1.8? F). Even a limited
rise in average surface temperature might lead to at least partial melting of the polar
icecaps and hence a major rise in sea level, along with other severe environmental
disturbances. An example of a runaway greenhouse effect is Earth's near-twin planetary
neighbor Venus. Because of Venus's thick CO2 atmosphere, the planet's cloud-covered
surface is hot enough to melt lead.
Water vapor is an important "greenhouse" gas. It is a major reason why humid regions
experience less cooling at night than do dry regions,. However, variations in the
atmosphere's CO2 content are what have played a major role in past climatic changes. In
recent decades there has been a global increase in atmospheric CO2, largely as a result
of the burning of fossil fuels. If the many other determinants of the Earth's present
global climate remain more or less constant, the CO2 increase should raise the average
temperature at the Earth's surface. As the atmosphere warmed, the amount of H2O would
probably also increase, because warm air can contain more H2O than can cooler air. This
process might go on indefinitely. On the other hand, reverse processes could develop
such as increased cloud cover and increased absorption of CO2 by phytoplankton in the
ocean. These would act as natural feedbacks, lowering temperatures.8
In fact, a great deal remains unknown about the cycling of carbon through the
environment, and in particular about the role of oceans in this atmospheric carbon cycle.
Many further uncertainties exist in greenhouse-effect studies because the temperature
records being used tend to represent the warmer urban areas rather than the global
environment. Beyond that, the effects of CH4, natural trace gases, and industrial
pollutants--indeed, the complex interactions of all of these climate controls working
together--are only beginning to be understood by workers in the environmental sciences.2
Despite such uncertainties, numerous scientists have maintained that the rise in global
temperatures in the 1980s and early 1990s is a result of the greenhouse effect. A
report issued in 1990 by the Intergovernmental Panel on Climate Change (IPCC), prepared
by 170 scientists worldwide, further warned that the effect could continue to increase
markedly. Most major Western industrial nations have pledged to stabilize or reduce
their CO2 emissions during the 1990s. The U.S. pledge thus far concerns only
chlorofluorocarbons (CFCs). CFCs attack the Ozone Layer and contribute thereby to the
greenhouse effect, because the ozone layer protects the growth of ocean phytoplankton.
Bibliography
Bilger, B., Global Warming (1992)
Bolin, Bert, et al., The Greenhouse Effect, Climatic Change and Ecosystems (1986)
Bright, M., The Greenhouse Effect (1991)
Fisher, David E., Fire and Ice: The Greenhouse Effect, Ozone Depletion, and Nuclear
Winter (1990)
Houghton, J., et al., eds., Climate Change: The IPCC Scientific Assessment (1990)
Monastersky, Richard, "Time for Action," Science News, Mar. 30, 1991
Moss, M., and Rahman, S., Climate and Man's Environment (1986)
Schneider, S. H., Global Warming (1989)
Seitz, F., Scientific Perspectives on the Greenhouse Problem (1990)
Shands, W. E., and Hoffmann, J. S., The Greenhouse Effect, Climatic Change, and U. S.
Forests (1987)
Stone, P., "Forecast Cloudy," Technology Review, Feb./Mar. 1992
Weiner, Jonathan, The Next One Hundred Years: Shaping the Fate of Our Living Earth
(1990)
Wuebbles, D., Primer on Greenhouse Gases (1991).
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