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Location: Pantego, Texas, United States

Saturday, July 18, 2009

The world encountered significant warming about 14,000 to 15,000 years ago that melted the glaciers that covered most of North America. That seems to have been a good thing from the standpoint of humans. The event was not unprecedented; there had been about 20 cycles of 100,000 years of ice followed by a shorter interglacial interval. Man does not appear to have been a factor in these cooling and heating cycles, and the natural mechanism that caused the changes is uncertain. The earth underwent a "little ice age" from around 1300 AD to 1800 AD. Temperature started increasing at 1 to 1.2 degree F per century around 1800, a trend that initially was assumed to be due to natural causes. In the early 1900's man started burning a lot of fossil fuels that added CO2 to the atmosphere. At present the CO2 concentration in the atmosphere is about 40% higher than it was in pre-industrial times. CO2 is a greenhouse gas that absorbs infrared radiation at wavelengths of 2.7, 4.3, and 15 microns. Around 1970 or so, some scientists became concerned that the increased level of CO2 would cause a high degree of warming of earth because the slight air temperature increase due to the increased CO2 concentration would allow an increase in the amount of water vapor, the dominant greenhouse gas, in the air. This would lead to furter warming resulting in melting of polar ice caps, resulting in more temperature increase as less sunlight is reflected. General circulation models were constructed which were calibrated with the assumption that increased CO2 rather than the unknown natural effects that previously must have been causing warming were now the cause. With this assumption, projected future increases in the CO2 concentration would necessarily lead to higher temperature projections. The GCMs became the proof that man-made global warming was happening. But, there are some logical fallacies in using the GCM computer output as proof. I have written about some of these issues before. Here is an article discussing this issue.

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