Sweden's Royal Academy of Sciences on Thursday named American scientist Wallace S. Broecker as the 2006 prizewinner in geosciences. Here is a quote from Dr. Broecker:
"My lifetime study of Earth's climate system has humbled me. I'm convinced that we have greatly underestimated the complexity of this system. The importance of obscure phenomena, ranging from those that control the size of raindrops to those that control the amount of water pouring into the deep sea from the shelves of the Antarctic continent, makes reliable modeling very difficult, if not impossible."
(11 of 13) [02/12/2003 10:05:30] Wallace S. Broecker, "Will Our Ride into the Greenhouse Future be a Smooth One?" GSA Today 5/97
Dr Broecker wrote in part: "The climate record kept in ice and in sediment reveals that since the invention of agriculture some 8000 yr ago, climate has remained remarkably stable. By contrast, during the preceding 100,000 yr, climate underwent frequent, very large, and often extremely abrupt shifts. Furthermore, these shifts occurred in lockstep across the globe. They seem to be telling us that Earth's climate system has several distinct and quite different modes of operation and that it can jump from one of these modes to another in a matter of a decade or two. So far, we know of only one element of the climate system which has multiple modes of operation: the oceans' thermohaline circulation. Numerous model simulations reveal that this circulation is quite sensitive to the freshwater budget in the high-latitude regions where deep waters form. Perhaps the mode shifts revealed in the climate record were initiated in the sea. This discovery complicates predictions of the consequences of the ongoing buildup of greenhouse gases in the atmosphere...." HERE
bttt
I would think if there were global shifts in climate over a relatively short period, we should look outside the Earth's ecosystem for the cause- say to the Sun.