Day After Tomorrow will never come

Following on from the comments by MITs Carl Wunsch that the Gulf Stream is safe as long as the wind blows and the Earth turns, several other scientists have used the pages of Science magazine (Apr. 16) to pour scorn on the conceit behind the forthcoming movie, The Day After Tomorrow.  The movie is predicated on the idea that unchecked global warming will cause an abrupt climate shift that will cause a new ice age in the United States.

Canadian scientists Andrew Weaver of the University of Victoria and Claude Hillaire-Marcel of the Universit de Quebec Montreal tackled the subject in a Perspectives article entitled, Global Warming and the Next Ice Age.  They pointed out that the view of global warming causing an ice age prevails in the popular press despite a relatively solid understanding of glacial inception and growth.

The scientists review of the literature concluded that, It is certainly true that if the AMO [Atlantic Meriodonal Oscillation] were to become inactive, substantial short-term cooling would result in western Europe, especially during the winter.  However, it is important to emphasize that not a single coupled model assessed by the 2001 IPCC Working Group I on Climate Change Science (4) predicted a collapse in the AMO during the 21st century.  Even in those models where the AMO was found to weaken during the 21st century, there would still be warming over Europe due to the radiative forcing associated with increased levels of greenhouse gases.

Pointing out that models that do show AMO collapse are not flux-adjusted like newer models, they conclude, Even the recent observations of freshening in the North Atlantic (a reduction of salinity due to the addition of freshwater) appear to be consistent with the projections of perhaps the most sophisticated nonflux adjusted model.  Ironically, this model suggests that such freshening is associated with an increased AMO (16).  This same model proposes that it is only Labrador Sea Water formation that is susceptible to collapse in response to global warming.

In light of the paleoclimate record and our understanding of the contemporary climate system, it is safe to say that global warming will not lead to the onset of a new ice age.  These same records suggest that it is highly unlikely that global warming will lead to a widespread collapse of the AMOdespite the appealing possibility raised in two recent studiesalthough it is possible that deep convection in the Labrador Sea will cease.  Such an event would have much more minor consequences on the climate downstream over Europe.

In the same issue, pioneering oceanographer Wallace Broecker dismisses the recent report rejected by the Pentagon that is predicated on a similar scenario.  He comments in his letter, Exaggerated scenarios serve only to intensify the existing polarization over global warming.