The past ten thousand years has seen two special phenomena: The Earth climate has been unusually stable and human civilizations emerged. Could it be that the latter was only possible because of the former? (There is evidence that the emergence of hominids in Africa a few million years ago was also triggered by climate effects with a resulting reduction of forested land area.)
One important factor in stabilizing the climate fluctuations seems to be the "great oceanic conveyor belt" that kept pumping the equivalent of one Peta Watt (= 1015 Watt, the power of about a million nuclear power plants) of warm water to the North Atlantic. It could be show that every time a rapid climate change took place it was connected with a switching of the North Atlantic conveyor belt, technically known as "Thermo-Haline Circulation (THC)" (See also the article by J. Marotzke (9.1) and ComDig 1999.beta 2.10, 1999.beta6.2). This switching seems to be so sensitively dependent on detailed parameter configurations that current (coarse) general atmospheric circulation models could not reproduce this empirical feature. It appears to be one of the situations where the "butterfly effect" of chaos theory can play a role in the unpredictability of climate changes.
The situation is very different in the Pacific ocean where large scale circulations are mainly driven by wind patterns and therefore do not affect deep layers of the ocean. But the formation of convecting air is also "tippy" in the sense that small changes in initial conditions can either switch the convection system on or off. One of the parameters that have an impact on the wind patterns in the Pacific is the retreat of the ice around the Antarctic. Pierrehumbert even points out scenarios under which one of the most robust wind patterns the tropical easterly trade winds of the Pacific -familiar to many seafaring generations- could be turned off. He concludes: " If one is tugging on the dragon's tail with little notion of how much agitation is required to wake him, one must be pre-pared for the unexpected."
* The Tropical Pacific: The Sleeping Dragon Wakes, Pierrehumbert, R. T. , PNAS, Vol. 97, 1355–1358, 15 Feb 2000
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