Measurements from Antarctic ice cores show that just before industrial emissions began, atmospheric CO₂ levels were about 280 parts per million by volume (ppm). The CO₂ concentrations stayed between 260 and 280 ppm during the preceding 10,000 years. According to the IPCC, concentrations of carbon dioxide in the atmosphere are at their highest levels for at least 650,000 years. The rapid increase in carbon dioxide levels began with the onset of the industrial revolution. The primary source of increase in carbon dioxide is fossil fuel use, but land use changes also make a contribution. The amount of methane in the atmosphere in 2005 (1774 ppm) by far exceeds the natural range of the last 650,000 years (320 to 790 ppm). The primary source of increase in methane is very likely (>90% confidence) to be a combination of human agricultural activities and fossil fuel use.

http://zfacts.com/p/818.html | 01/18/12 07:18 GMT
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