GLOBAL warming will wreck attempts to save the Amazon rainforest, according to a devastating new study that predicts that one-third of its trees will be killed by even modest temperature rises.
The research, by British climate change specialists, shows even severe cuts in deforestation and carbon emissions will fail to save the rainforest, the destruction of which has become a powerful symbol of human impact on the planet.
Up to 85 per cent of the forest could be lost if greenhouse gas emissions were not brought under control, the experts said. Even under the most optimistic climate change scenarios, the destruction of large parts of the forest was "irreversible".
Vicky Pope, of the British Meteorological Office's Hadley Centre, which carried out the study, said: "The impacts of climate change on the Amazon are much worse than we thought. As temperatures rise quickly over the coming century, the damage to the forest won't be obvious straight away, but we could be storing up trouble for the future."
Tim Lenton, a climate expert at the University of East Anglia, England, called the study, presented at a global warming conference in Copenhagen on Wednesday, a "bombshell". He said: "When I was young I thought chopping down the trees would destroy the forest but now it seems that climate change will deliver the killer blow."
The study, which has been submitted to the journal Nature Geoscience, used computer models to investigate how the Amazon would respond to future temperature rises. It found that a two-degree rise above pre-industrial levels, widely considered the best-case global warming scenario and the target for ambitious international plans to curb emissions, would still see 20 to 40 per cent of the Amazon die off within 100 years.
A three-degree rise would see 75 per cent of the forest destroyed by drought over the following century, while a four-degree rise would kill 85 per cent.
Experts had previously predicted that global warming could cause significant "die-back" of the Amazon. The new research is the first to quantify the long-term effect.
Chris Jones, who led the research, told the conference: "A temperature rise of anything over one degree commits you to some future loss of Amazon forest. On any kind of pragmatic timescale, I think we should see loss of the Amazon forest as irreversible."
Peter Cox, professor of climate system dynamics at the University of Exeter, said the effects would be felt around the world. "Ecologically it would be a catastrophe and it would be taking a huge chance with our own climate. The tropics are drivers of the world's weather systems and killing the Amazon is likely to change them forever. We don't know exactly what would happen but we could expect more extreme weather."
Huge Amazon loss would amplify global warming "significantly" he said. "Destroying the Amazon would also turn what is a significant carbon sink into a significant source."
Even with drastic cuts in emissions in the next decade, scientists say there will be only about a 50 per cent chance of keeping global temperature rises below two degrees.
Environmental campaigners said they were alarmed by the predictions. "With a rise of over two degrees, you begin to see a large-scale change to savannah," said Beatrix Richards, head of forest policy and trade at WWF UK. "You also lose major ecosystem services, such as keeping carbon levels stable, providing indigenous people with goods and services, and balancing rainfall patterns globally from the US grain belt to as far away as Kazakhstan.
"A four-degree (rise) is a nightmare scenario that would move us into uncharted territory."