Catastrophic climate change '90% certain'

The world is 90 per cent certain to experience a potentially catastrophic global warming over the next century caused by man-made emissions of greenhouse gases, scientists say.

New estimates suggest that there is a nine out of ten chance that the Earth will warm by between 1.7C and 4.9C by 2100, generating serious disturbances to the climate and a rise in sea levels.

The fresh probability estimates are made by Tom Wigley of the National Center for Atmospheric Research in Boulder, Colorado and Sarah Raper of the University of East Anglia in Norwich in a study published today in the journal Science.

The two scientists used computer models to build on the work of the third report of the Intergovernmental Panel on Climate Change, which was published last week and predicted that global temperatures would rise by between 1.4C and 5.8C.

However, the panel did not assign estimates of probability to its predictions because of the difficulty of reaching a consensus between the hundreds of scientists involved in compiling the report, said Dr Raper, who sits on one of the panel's working groups.

"We're not trying to criticise the IPCC, it's just that we can as individuals go a step further. It's important because you cannot assess a risk without assigning a probability of it happening," Dr Raper said.

The temperature range given by the two scientists was slightly narrower than that given by the panel and it assumed that no measures were taken to mitigate the effects of climate change, the researchers said.

As early as 2030, the planet was likely to heat up by between 1C and 2C, and by 2100 we were likely to experience global warming that was five times greater than the entire warming seen in the 20th century, they said.

"Whether or not such rapid warming will occur ... depends on actions taken to control climate change," the scientists say in their Science paper.

However, even rapid attempts to mitigate the effects of global warming were unlikely to have an impact for many years. "The climate's inertia would lead to only a slow response to such efforts and guarantee that future warming would still be large," they say.

Professor Wigley said it was important to assess the likelihood of the different scenarios envisaged by the panel because, if all of them were thought to be equally likely, that made planning difficult.

"We are assigning probabilities to long-term projections to aid policy makers in assessing the risks that might accompany various courses of action or non-action," Professor Wigley explained.