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
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"Global Warming." StudyMode.com. 10, 1999. Accessed 10, 1999. http://www.studymode.com/essays/Global-Warming-1562.html.