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Location: Pantego, Texas, United States

Friday, March 06, 2009

People usually do not realize that the basis for the apocalyptic global warming hypothesis relates to water vapor rather than atmospheric CO2 buildup. Everyone agrees that CO2 is a greenhouse gas, and that increased concentration in the atmosphere will cause a slight increase in atmospheric temperature over what would otherwise exist. The global warming hypothesis is that this slight increase in temperature will cause an increase in amount of water vapor in the atmosphere because it is assumed that the relative humidity of water vapor will remain constant. (This assumption was never verified as far as I know, but it sounded reasonable as a first guess.) By the Clausius-Clapyron equation, a higher atmospheric temperature will support more water vapor in the air. Water vapor is a greenhouse gas, so an increase will cause temperature to go up even more. This is called a positive feedback. The General Circulation Models (GCMs) used by the IPCC are programmed with this positive feedback. The GCMs have another problem with water vapor in that they are not able to calculate cloud cover using first principles of physics. For one thing, the grid elements in the GCMs are very large compared to cloud formations. As a consequence, heuristic, or rule of thumb, methods are used to create the cloud cover computations in the GCMs. It is obvious to everyone that clouds have a strong impact on atmospheric temperature. Low level clouds reduce temperature in the daytime and increase temperature at night. In the GCMs cloud cover is a positive feedback to atmospheric temperature. This deficiency with clouds cause some people to doubt the accuracy of GCMs. There is a lot of debate about what causes cloud formation, and it is clear that the GCMs do not use physics to compute cloud formation. In fact, if cosmic rays are a significant trigger, it would not even be possible to compute future behavior because the future cosmic ray flux is not only unknown, but is unknowable. But, back to the water vapor assumption. There has been some indication that relative humidity does not increase as atmospheric temperature increases. This would mean that water vapor is a negative rather than a positive feedback. I have always thought that might be the case based on a qualitative assessment rather than specific data. The reason is that CO2 has been an order of magnitude higher in the past than it is now, and temperature obviously did not spiral upward out of control. Then there is consideration of the Medieval Warm Period when temperature was higher than it is now. Again, temperature obviously did not spiral upward. (This type of logic is why the AGW advocates worked so hard with the now discredited Mann hockeystick to try to eliminate the Medieval Warm Period.) Now there is a paper that indicates that water vapor is a negative feedback. The AGW advocates will have to attack this with vigor because it severely damages the AGW hypothesis.

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