Scientists in climate change warning

Even the most drastic greenhouse gas cuts currently being discussed stand little chance of limiting global warming to safe levels, studies by scientists in Oxford and Germany have found.

Scientists have worked out the "carbon budget" - the total such gases the world can emit without risking a catastrophic "tipping point" of warming. The studies put this budget at about 1,000bn tonnes of carbon.

This means that less than a quarter of proven and economically recoverable fossil fuel reserves can be burnt between now and 2050 to avoid a jump of more than 2°C above pre-industrial levels - widely regarded by scientists as the limit of safety.

It would mean, for instance, that Canada would have to leave its oil tar sands untapped, and Saudi Arabia would need to leave most of its oil reserves in the ground to avert disaster.

The findings, published today in the peer review journal Nature, have prompted calls for a radical rethink on tackling climate change.

"If we continue burning fossil fuels as we do, we will have exhausted the carbon budget in merely 20 years and global warming will go well beyond two degrees," said Malte Meinshausen, of the Potsdam Institute, lead author of one of the studies.

At more than two degrees of warming, climate change becomes irreversible and in many cases catastrophic, according to the Intergovernmental Panel on Climate Change. Sea level rises, droughts, floods, heatwaves and more intense storms would result.

"This changes the way we think about climate change," said Myles Allen, of Oxford University, one of the lead authors. "It's something for policymakers to chew on."