Global Warming

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.

The causes of warming, the greenhouse gasses

Carbon dioxide, methane, and nitrous oxide are responsible for 80% of the warming due to the greenhouse effect. CFC's HCFC's and CF's (used as refrigerants) contribute another 5% even though their concentration is much smaller.
  Preindustrial Concentration Concentration in 1994  Annual Rate of Increase Lifetime  Importance to Greenhouse Effect
Carbon dioxide  280ppmv  358ppm  0.4%  50-200

 57%
 Methane  700ppbv  1,720ppbv  0.6%  12

 17%
 Nitrous Oxide  275ppbv  312ppbv  0.25%  120

  5%
HCFC-22  0  110pptv  5% 12

<5%
Source: Ristinen, R &Kraushaar, J, Energy and the Environment, 1999, Wiley & Sons. Notice the change in units, CO2 is measured in parts per million, Methane per billion, and HCFC per trillion.

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.

ANTHROPOGENIC SOURCES OF METHANE

 Landfills & Sewage

 Energy Production

 Agricultural

 10.4 mmt

 10.0 mmt

 8.6 mmt
Source:Department of Energy, Annual Energy Review

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

Consequences of warmer temperatures

* Effects on precipitation and local weather from temperature changes.
* Decrease in the strength of ocean currents with the possibility of rapid change in climate.
* Increase in frequency of severe storms and weather anomalies.
* Sea level rise due to melting of ice, and expansion of the ocean water.
* Increase of tropical disease in temperate climates.
* Poleward shift in ecosystems at a rate faster than some plants and animals can migrate resulting in more rapid extinctions.
* Decrease in grain production due to decrease in precipitation in many grin growing areas.
* Reduction of forests due to a variety of causes including changes in frost free periods, draught stress, insect damage.
 
References:
 
 
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