Hertzberg: More on climate science
The overwhelming majority of the land area of the Earth is in the Northern Hemisphere, and since it is land surface that causes most of the temperature extremes, it is the variation in solar insolation on the land surface of the Northern Hemisphere that accounts for the Milankovitch cycles of global glacial coolings and interglacial warmings. While it is true that currently the Earth’s elliptical orbit puts us further from the sun in Northern Hemisphere summer so that the daily solar insolation is reduced, it is completely erroneous to conclude therefore that “the Earth should have been cooling rather than warming for the last 8,000 years” as Pharr claims based on the Hays et. al. article. They make the same mistake made not just in that Science article, but in Scientific American articles, and in many textbooks.
What they fail to realize is that when the Earth is further away from the sun it moves more slowly in its orbit. Go to your calendar and mark the two equinoxes. Then count the number of days on the summer side of our orbit and compare it to the number of days on the winter side. The summer half of our orbit lasts about one week longer and that is more significant than the reduction in daily solar insolation caused by our further distance from the sun. Exposure time matters, and that extra week of summer sun is the reason we have been in an interglacial warming for the last 8,000 years. So Pharr and Hays et. al. make reference to Milankovitch but have misinterpreted the details of his theory.
Next, Pharr regurgitates the argument used to try to reconcile their false greenhouse warming theory with the Milankovitch cycles of global coolings and interglacial warmings whose cycle of about 100,000 or so years matches the changes in the ellipticity of the Earth’s orbit.
They argue that the Milankovitch orbital cycles are “weak forcings” that initiate an interglacial warming but which are then amplified by the “strong forcing” of greenhouse warming as CO2 is emitted from the ocean as the warming proceeds. As propagandists, they select only one-half of the cycle and dutifully ignore the other half. If their mechanism is correct, then what causes the glacial cooling that follows the glacial warming? How can the weak orbital forcing overcome the strong forcing of the greenhouse effect when the CO2 concentration is at its maximum value at the peak of the interglacial warming? They are completely out on a limb at that point. But one has to feel sorry for them, for after all, they are in the global warming business: global cooling is someone else’s job!
The reality is that those long-term cycles are driven entirely by variations in the Earth’s orbital parameters and the trivial variations in atmospheric CO2 from about 0.02 to 0.03 percent that follow those cycles are of no consequence to weather. They are the effect of coolings and warmings and not their cause, and even those variations occurred long before any human emission of CO2.
For more details on this issue than can be presented in such a letter to the editor, the reader is referred to my recent Cafe Scientifique talk which can be accessed by going to http://www.youtube.com and entering “climategate” and “hertzberg” in the search box. The talk is presented there is seven segments each somewhat less than 10 minutes in duration.
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