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A question of balance

Both papers present the accepted view of the Milankovitch Cycles as the primary driver of glacial-interglacial variation during the Pleistocene Ice Age. The Roe paper clearly states “the relatively small amplitude of the CO2 radiative forcing and the absence of a lead over dV/dt both suggest that CO2 variations play a relatively weak role in driving changes in global ice volume compared to insolation variations.” He does hedge his bets regarding carbon dioxide's impact on tropical regions or how the rapid transition from glacial to interglacial are driven by the cycles, but others have addressed that issue as well (see “New Study Adds To Glacial Ice Confusion” and “The Sun, Not CO2, Caused Ice Age Glaciers To Melt”).

In fact, the Lindzen and Pan paper addresses the “profound variations in the flux of heat from the tropics to higher latitudes.” They claim that the cycles (in this case precession) can cause major variations in the Hadley circulation. The Hadley circulation is a closed circulation loop, which begins at the equator with warm, moist air lifted and carries that warmth poleward. The paper I just described claims that it is not precession responsible for this influence but obliquity.

Effectively, the impact of relatively small variation in insolation on global temperatures is amplified by changes in atmospheric circulation (Lindzen claims by 2x). In the end, Earth's climate is all about balancing the influx of energy from the Sun and the outflow of energy back into space. The CO2 crowd claim that insolation, whether caused by the cycles or by changes in solar activity, is not sufficient to drive climate change. Well, neither is CO2's GHG effect. However, the physical feedbacks that are linked to insolation are much better established than any hypothetical feedbacks assumed to be leveraged by carbon dioxide levels.

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