The disappearance of the Amazon forest is probably unstoppable because of the climate change already occurring, according to the UK's latest computer models of the climate.
Temperatures up to seven degrees higher than today and decreases in rainfall of up to 50 centimetres a year will kill off vast areas of what is now lush tropical forest, the world's richest wildlife habitat, and turn it into grassland or even desert.
But even more critically, the Amazon and other forested regions will be transformed from areas which now absorb carbon dioxide, the principal gas causing global warming, into areas which give it out.
The result will be an enormous and relatively sudden increase in the amount of carbon dioxide in the atmosphere, perhaps more than 50 per cent, and a rapid or even runaway escalation of climate change in a "positive feedback loop" - global warming causing more global warming.
The predictions, some of the direst yet, were unveiled yesterday by the Environment minister, Michael Meacher, to coincide with the opening of the two-week conference in Buenos Aires, Argentina, which will try to carry forward last year's Kyoto climate change treaty.
"They make frightening reading," Mr Meacher said.
They come from Britain's latest supercomputer model of the global climate at the Meteorological Office's Hadley Centre for Climate Research in Bracknell, Berkshire, and five associated models of areas of potential impact - food production, water supplies, flood risk, human health and natural vegetation cover.
The predictions about Brazil come from the natural vegetation model run by the Institute of Terrestrial Ecology (ITE) in Edinburgh. This is the first time anyone has put a date on the death of the Amazon rainforest, and it suggests a very rapid end.
"The ecosystem model predicts that [forest] dieback will occur over vast areas of northern Brazil, beginning in the 2040s," the government report says. "After 2050, and as a result of vegetation dieback and change, primarily in Amazonia, Europe and North America, the terrestrial land surface becomes a source of carbon, releasing approximately 2 billion tonnes of carbon per year into the atmosphere."
At the moment the trees are absorbing between two and three billion tonnes of carbon dioxide a year - nearly half the amount that is released from man-made sources.
"It is absolutely essential that world-wide political action is taken, going further than Kyoto to arrest and ultimately reverse this process," Mr Meacher said.
t Because of an error in the editing process, early editions of yesterday's Independent said scientists at the Climatic Research Unit of the University of East Anglia were predicting 1998 would be Britain's hottest year for the past thousand years. In fact, as later editions correctly stated, the prediction is that it will be the hottest year in the current millennium for the world as a whole, not for Britain.
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