Pentagon report suggests global warming could trigger catastrophic freezing.

In January, the Pentagon shared with Fortune Magazine a report that had gathered the analyses of leading climate scientists to forecast possible political, social, and environmental scenarios if today's releases of greenhouse gases triggered "abrupt climate change"--a kind of disruption that could conceivably occur in as short a period as a decade. Abrupt climate change could be triggered by an ice-melt-driven collapse or disruption of the "Ocean Conveyor," a global current that circulates warmer, saltier water from the equator to the colder polar regions. This "oceanic heat pump" (of which the Gulf Stream is a part) plays a key role in keeping Europe and North America warm, and significantly moderates winter temperatures.

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The Pentagon report suggested that abrupt climate change could trigger a series of horrific destabilizing effects. A sudden drop of temperature in North America and Europe could disrupt agricultural production and increase already growing demand for fossil fuels. In addition, as the Ocean Conveyor plays a key role in the global hydrological cycle, its disruption could cause "megadroughts" in some areas, such as the southern United States, and violent storms in many others. Further, the authors forecast that these changes could trigger political instabilities, immense transfers of refugees in destabilized areas, and possibly even wars over increasingly taxed resources.

The report was primarily conducted as an analytical exercise in order to consider the effect abrupt climate change would have on US security. More importantly, it draws attention to how catastrophic climate change could be to human society--not just as average temperatures increase gradually and sea levels rise slowly, but in potentially triggering a new ice age.

The Pentagon report doesn't come entirely out of the blue. In January 2003, Woods Hole Oceanographic Institution president Robert Gagosian presented a briefing to the World Economic Forum in Davos, Switzerland showing evidence that the North Atlantic--the "Achilles' Heel" of the Ocean Conveyor system--is flooding with fresh water (due to changing precipitation patterns and increased melting of glaciers and Arctic sea ice). This transfusion of fresh water could disrupt or even shut down the Conveyor. According to the National Academy of Sciences report, "available evidence suggests that abrupt climate changes are not only possible but likely in the future, potentially with large impacts on ecosystems and societies." David King, the chief scientific advisor to the UK government, warned January that "climate change is the most severe problem that we are facing today--more serious than the threat of terrorism."