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Unformatted text preview: : N2 , O 2 , CO2 , and H2 O vapor. This radiant energy is absorbed by Earth's
oceans and land areas and warms the surface. All warm objects radiate infrared radiation, called IR. The oceans
and land areas emit IR, which passes directly through N2 and O2 into outer space. The loss of this energy would
mean that the Earth would be a cooler place. However, CO2 (g) and H2 O(g) absorb IR, and in effect slow down
the loss of heat from the surface. Therefore, Earth's surface is many degrees warmer than it would be without
CO2 (g) and H2 O(g) in the air. This is the so-called greenhouse effect. Some carbon dioxide has always been
present in the atmosphere, and some warming is considered desirable. Since atmospheric carbon dioxide is
increasing at the rate of 1 ppm per year, this is expected to lead to an "enhanced greenhouse effect."
Greenhouse gases reduce the heat loss to outer space by absorbing IR. Infrared radiation increases the
vibrational energy level of molecules that absorb it. Then these vibrationally excited molecules reemit IR as
they drop to the ground state. Statistically 1/2 of the IR is aimed downward toward Earth's surface, and 1/2 is
aimed upward toward outer space. The IR aimed back toward the surface eventually causes the temperature of the
air to rise.
Scientists have been trying for many years to estimate rates of global warming and its effects. The carbon
dioxide content of the atmosphere is expected to double by the year 2050. Some of the predicted effects are:
3. A temperature increase of 3°C to 5°C by that year.
Melting of glaciers and icecaps that will cause a 2-ft rise in sea level with its accompanying flooding of sea
coasts and major cities.
Widespread changes in climate. Suggestions to lower carbon dioxide emissions center around less dependence on fossil fuels for energy.
Carbon dioxide emissions could be reduced by increasing efficiency of automobiles, home heating, and electric
power production. Additional reduction could result from replacing existing fossil fuel electric...
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- Spring '08