Monday, November 27, 2006

Greenhouse Gases

Greenhouse gases (GHGs) are gaseous components of the atmosphere that contribute to the "greenhouse effect". Although uncertainty exists about exactly how earth's climate responds to these gases, global temperatures are rising. Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases.

When sunlight reaches the Earth's surface, some is absorbed and warms the earth. Because the earth is much cooler than the sun, it radiates energy at much longer wavelengths than the sun (see Black body radiation and When's displacement law); some of these longer wavelengths are absorbed by greenhouse gases in the atmosphere before they are lost to space. The absorption of this longwave radiant energy warms the atmosphere (the atmosphere also is warmed by transfer of sensible and latent heat from the surface). Greenhouse gases also emit longwave radiation both upward to space and downward to the surface. The downward part of this longwave radiation emitted by the atmosphere is the "greenhouse effect." The term is in fact a misnomer, as this process is not the primary mechanism that warms greenhouses.
The major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide, which causes 9-26%; methane which causes 4-9%, and ozone, which causes 3-7%. Note that it is not really possible to assert that a certain gas causes a certain percentage of the greenhouse effect, because the influences of the various gases are not additive. (The higher ends of the ranges quoted are for the gas alone; the lower ends, for the gas counting overlaps.)

2 comments:

Anonymous said...

i think you had made very good points from now on i will use eco friendly thing instead of things that damage the earth.Thank you for posting i think that i will treat my dogs and hamsters better from now on!
thx :)

cell said...

your welcome :D