Riding on its coat tails is an army of environmentalists hoping it will win new recruits to their cause.

Roland Emmerich of "Independence Day" and "Godzilla" fame directs a story of how global warming caused by man's insatiable desire to keep burning oil, gas and coal, melts the polar ice caps and neutralizes warm ocean currents to trigger an Ice Age.

New York is flooded by a tidal wave and then frozen solid in a giant ice storm. Americans flee south to the Mexican border where they negotiate entry in exchange for forgiveness of all Latin American debt.

Campaigners at a pre-release screening on Tuesday in Britain conceded that the film was pure fiction that defied the laws of physics and bore no relation to the impacts they say global warming is already having.

Nevertheless, most said it would bring the real debate on climate change to people who would not otherwise consider it.

"I was disappointed by how little there was by way of reference to why climate change happens, but it still widens the opportunity to talk about it," said Brenda Boardman of the University of Oxford's Environmental Change Institute.

Some scientists fear the film will trivialize the debate.

"This (plot) is completely different from the way we think climate change is going to happen," said Mike Hume, executive director of the Tyndall Center for Climate Change Research.

"Good science, good film making and good politics rarely go together."

Fox has carefully sidestepped any direct link with "green" campaigners, and even resisted their overtures at first, but Dennis Quaid, who stars as a climatologist, and teenage pin-up Jake Gyllenhaal, who plays his son, are helping out.

Emmerich himself was persuaded by the green group Future Forests to make the movie "carbon neutral." He paid $200,000 on a reforestation project in the Himalayas and energy saving projects for poor families in the United States to offset the carbon energy used during filming.

According to The New York Times, climatologists at the U.S. space agency NASA were told not to comment on the film for fear of upsetting a U.S. administration that has refused to sign the global Kyoto Protocol aimed at reducing carbon emissions to curb climate change.