Introduction
I was astonished to read Alexander Cockburn’s essay in the April 28th online edition of Counterpunch entitled “Is Global Warming a Sin?” [i] Cockburn’s thesis is that there is no scientific evidence whatsoever linking anthropogenic (human caused) CO2 emissions with worldwide increases in mean temperature “global warming.” Comparing the proposed sale of carbon credits to alleviate future global warming to the medieval practice of the Catholic Church selling indulgences to cancel past sins, Cockburn asserts:
"There is still zero empirical evidence that anthropogenic production of CO2 is making any measurable contribution to the world's present warming trend. The greenhouse fearmongers rely entirely on unverified, crudely oversimplified computer models to finger mankind's sinful contribution. Devoid of any sustaining scientific basis, carbon trafficking is powered by guilt, credulity, cynicism and greed, just like the old indulgences, though at least the latter produced beautiful monuments." [ii]
Cockburn bases his conclusions upon the research of Dr. Martin Hertzberg whose conclusions he places above “all the counsels of Al Gore or the jeremiads of the IPCC (Inter-Governmental Panel on Climate Change).” Fair enough, Cockburn wishes to disregard the careful, published, peer-reviewed, findings of essentially the entire global scientific community, in favor of the assertions of his favored climatologist. He can do that; however, we are not compelled follow his astounding leap of judgment. Fairness however, does require me to carefully evaluate and consider Hertzberg’s rival global warming hypothesis and its several assertions.
The Hertzberg-Cockburn Critique of Global Warming
What are these assertions of Hertzberg’s hypothesis? His argument is that temperature changes are driven by long-term changes in the amount of sunlight striking the Earth. These changes are caused by Milankovitch cycles, named for the Serbian scientist who first described them. Wikipedia defines these as follows:
"Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milankovitch. The eccentricity, axial tilt, and precession of the Earth's orbit vary in several patterns, resulting in 100,000 year ice age cycles of the Quaternary glaciation over the last few million years. The Earth's axis completes one full cycle of precession approximately every 26,000 years. At the same time, the elliptical orbit rotates, more slowly, leading to a 22,000 year cycle in the equinoxes. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit changes from 21.5 degrees to 24.5 degrees and back again on a 41,000 year cycle. Presently, this angle is 23.44 degrees. The Milankovitch theory of climate change is not perfectly worked out; in particular, the largest observed response is at the 100,000 year timescale, but the forcing is apparently small at this scale, in regards to the ice ages. Various feedbacks (from carbon dioxide, or from ice sheet dynamics) are invoked to explain this discrepancy."
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