Antarctica is likely to be the world's only habitable continent by the end of this century if global warming remains unchecked, the Government's chief scientist, Professor Sir David King, said last week.
He said the Earth was entering the "first hot period" for 60 million years, when there was no ice on the planet and "the rest of the globe could not sustain human life". The warning - one of the starkest delivered by a top scientist - comes as ministers decide next week whether to weaken measures to cut the pollution that causes climate change, even though Tony Blair last week described the situation as "very, very critical indeed".
The Prime Minister - who was launching a new alliance of governments, businesses and pressure groups to tackle global warming - added that he could not think of "any bigger long-term question facing the world community".
Yet the Government is considering relaxing limits on emissions by industry under an EU scheme on Tuesday.
Sir David said that levels of carbon dioxide in the atmosphere - the main "green- house gas" causing climate change - were already 50 per cent higher than at any time in the past 420,000 years. The last time they were at this level - 379 parts per million - was 60 million years ago during a rapid period of global warming, he said. Levels soared to 1,000 parts per million, causing a massive reduction of life.
"No ice was left on Earth. Antarctica was the best place for mammals to live, and the rest of the world would not sustain human life," he said.
Sir David warned that if the world did not curb its burning of fossil fuels "we will reach that level by 2100".