I have heard that a frog in a pot of cold water which is gradually brought to a boil, will not notice the heat until it is too late to jump out. Is this our fate also? Predictions of temperature rises of 2-4° C in 50-100 years seem almost inconsequential, but in fact the consequences are far reaching. Ever since James Lovelock retracted his Gaia Hypothesis, we cannot assume the existence of some inherent tendency for the planet to return to a stable equilibrium that is supportive of life. In fact, Harvard geologist Paul Hoffman has evidence that 550 to 700 million years ago the earth was a solid ice ball, 58 degrees below zero, far from the equilibrium temperatures we had considered possible.
| Preindustrial Concentration | Concentration in 1994 | Annual Rate of Increase | Lifetime | Importance to Greenhouse Effect | |
| Carbon dioxide | 280ppmv | 358ppm | 0.4% | 50-200 |
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| Methane | 700ppbv | 1,720ppbv | 0.6% | 12 |
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| Nitrous Oxide | 275ppbv | 312ppbv | 0.25% | 120 |
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| HCFC-22 | 0 | 110pptv | 5% | 12 |
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Carbon Dioxide - More information on the sources and effects of Carbon Dioxide is available on another page of this site.
Methane - Is produced by anaerobic decay. The principal Anthropogenic sources are rice paddies, garbage dumps and cattle. Methane is roughly 20 times more potent as a greenhouse gas than CO2 and is increasing at a higher rate in the atmosphere which will lead to its increasing importance in the near future. It has a shorter life half-life, however, which limits its ultimate concentration before its decay rate equals the rate of production. There are ways of reducing the anthropogenic sources of methane, such as capturing the methane emitted by landfills, and drying out rice paddies once a year. As a result it methane is not considered as significant a threat as CO2.
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Water Vapor - Is another greenhouse gas, but of a natural origin. It enters into the predictions as part of a positive feedback mechanism. As the planet warms up, the rate of evaporation and transpiration increases resulting in more water vapor in the air which in turn traps more heat. This effect is partially balanced by the increased cloud cover which tends to reduce the amount of solar radiation reaching the earth. The balance between the two effects is not yet clear.
Deforestation - Deforestation contributes to global warming in two ways. First, much of the clearing in the tropical rainforests is accomplished by burning the forest which releases CO2 immediately back into the atmosphere. Secondly the removal of the forests eliminates the most effective mechanism for removing carbon form the atmosphere. Thirdly, the loss of the forest canopy directly contributes to the heating of the earth locally through the loss of the cooling effect of the trees and the increase in reflectivity of the bare ground or cultivated crop.
A good overview of global warming and the carbon cycle from the Encyclopedia Britannica http://www.eb.com:180/bol/topic?artcl=106248&seq_nbr=11&page=n&isctn=4