dependence of temperature on CC>2 levels follows an approximately logarithmic relationship.71 Thus, a fourfold increase of CO2 levels would result in a doubling of the temperature increases in Table 2.8. However, these increases are averaged over the entire globe. The models tend to show fairly small temperature increases near the equator and fairly large temperature increases in the polar regions. In addition, the northern hemisphere is expected to warm slightly more than the southern hemisphere because of its greater land area and the larger thermal inertia of the southern oceans. The general circulation model of Manabe and Weatherald$6 predicted temperature increase of up to 10°C at high northern latitudes for a global temperature increase of 3°C. The climatic impacts of atmospheric warming due to CO2 would not be limited to surface temperature increases: higher temperatures could very likely produce a substantial increase in global precipitation.72 However, this does not mean that all regions of the earth would experience increased precipitation. Some areas may even experience decreased precipitation. It has been suggested that the western United States could be one of the latter areas.13 In addition, global warming may produce a decrease in the temporal variability of precipitation. Another consequence of global warming due to CO2 could be the alteration of atmospheric circulation patterns. With more warming at upper latitudes than at lower latitudes, the flux of heat from equator to pole will be decreased. This may serve to change the intensity and/or frequency of weather patterns. A warmer climate might seem to be beneficial from a standpoint of longer growing seasons, which would allow the production of more food. It has been estimated that an increase of 1°C in average annual temperature at a location is equivalent to about a 10-day increase in the growing season.72 However, an extremely rapid change in regional climate could prove to be detrimental rather than beneficial, because crops and other vegetation are adapted to existing conditions. Rapid changes in climate may result in reduced biological fitness and productivity before readjustments in human activities or in nature can be made.^O A potential impact of global wanning that has been frequently discussed is a rise in sea levels resulting from the melting of glacial ice. Complete
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