The projections are based on data from more than 50 climate models looking at the impact of greenhouse gas emissions.
The study appears in the Proceedings of the National Academy of Sciences. The researchers gathered results from 52 computer simulations to calculate the risks from climate-induced changes to the world's key ecosystems. They then grouped the results according to the amount of global warming: less than 2C (3.6F); 2-3C (3.6F-5.4F); and more than 3C (5.4F). For each of the temperature ranges, the team assessed the probability of changes in forest cover, the frequency of wildfires and changes to freshwater supplies over the next 200 years.
Marko Scholze, from the University of Bristol's Department of Earth Sciences, and the paper's lead author, said the findings revealed a direct link between rises in global temperature and damage to ecosystems.
"We show the steeply increasing risks, and increasingly large areas affected, associated with higher warming levels," he said. "The United Nations says we should limit greenhouse gas emissions so we do not have dangerous climate change. So the question is 'what is dangerous climate change?'.
"In this paper we define the level we think is dangerous and see how likely it will come true," Dr Scholze told BBC News. Richard Betts, manager of Climate Impacts at the Met Office's Hadley Centre, welcomed the findings.
"This makes an important new contribution to the debate on the effects of climate change," he said. "We already knew that we cannot rely on just one model, as different models give different answers.
"This work helps us go beyond that vague statement, as it shows how much the models agree on particular levels of impact and how much they disagree." He said the research was an important first step towards quantifying the risks of damaging impacts associated with particular levels of global warming.
The findings showed areas that would experience the worst forest loss would include Eurasia, eastern China, Canada and the Amazon. Areas of western Africa, southern Europe and eastern US states were at most risk from dwindling freshwater supplies and droughts as a result of rising temperatures. The data also showed that any temperature increase of more than 3C (5.4F) could result in land "carbon sinks" releasing their stored carbon into the atmosphere, exacerbating the problem of global warming.
Dr Scholze hoped the collated data would answer some of the concerns among more sceptical members of the scientific community who questioned the accuracy of climatic modelling.
"That is exactly why we did this study," he said. "We used as many models as we could and did not rely on any one study.
"We looked at 52 simulations and the probabilities of dangerous climate change these models showed."
Dr Betts agreed: "Of course it is risky to make these projections when models are continuously being changed, but we do have to make decisions on climate change now so if we wait for the perfect model we will be too late.
"The models give the best encapsulation of current understanding of the climate system, and are the only way of assessing physically plausible futures." Dr Scholze said he hoped the findings would be used in debates on dangerous climate change and the measures needed to avoid it.
Posted on 22nd August 2006
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