The science and the science fiction

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Drawing from some recent coverage, we offer an overview of what The Day After Tomorrow predicts (please take note that it's just a movie), and what scientists say is likely happen.

In the film: Global warming leads to an ice age.
The scientists say: In one report to the US Department of Defence earlier this year - before the film was released - two researchers suggested that a shutdown of the Gulf Stream could plunge the northern hemisphere into a deep freeze and trigger global famine within 15 years (others say centuries). Neither of the two doomsayers, it has been emphasised though, are climate scientists. Others agree that without the thermohaline circulation, not as much heat would be transported from the tropics to the North Atlantic region. According to models, eastern North America and western Europe would cool, while the rest of the world continues to warm, but no-one is sure how much of this cooling would be balanced by the simultaneous warming in the atmosphere.

In the film: Polar melting shuts down the Gulf Stream.
The scientists say: There is (general) consensus that the melting of arctic ice as described in the film - and forecast by many - may weaken the Gulf Stream's circulation, but would not halt it. Scientists describe the collapse of the thermohaline circulation as a high-impact but low-probability event (no-one knows how low, though). Some scientists believe, however, that a similar shutdown of the current took place at the end of the last ice age - some 11 000 or 13 000 years ago - when meltwater from an enormous glacier poured into the north Atlantic. A European winter followed, with temperatures of about 10^o Celsius below normal and cold spells that are said to have lasted for hundreds of years.

In the film: The weather flip-flops within days.
The scientists say: Not likely. And the filmmakers are quite candid about the artistic licence they took. Some scientists say it could take millennia for another ice age to occur, but are chary to discount abrupt climate changes. "Even as the Earth as a whole continues to warm gradually, large regions may experience a precipitous and disruptive shift into colder climates," wrote Robert Gagosian, president and director of the Woods Hole Oceanographic Institution, in a paper prepared for a panel on abrupt climate change at the World Economic Forum in Davos. Even then, though, scientists still think in terms of decades rather than days or weeks.

In the film: A repentant US vice-president, now president, sees the error of his ways and vows to do right by global warming.
The scientists say: Now there's science fiction for you.

Sources: BBC News, Nature, New Scientist, the Pew Centre on Global Climate Change.