Scientists warn of carbon danger levels

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 for the first time 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 the world's proven and economically recoverable fossil fuel re- serves can be burnt between now and 2050 to avoid a jump of more than two degrees celsius 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 in the peer review journal Nature today, 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.

Governments are being urged to consider more drastic measures than emissions cuts, including untried and exotic methods such as erecting mirrors in space.

“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.”

More than 100 governments have committed to halving global emissions by 2050, and many developed countries to reducing their emissions by 80 per cent by 2050, compared with 1990 levels. But the authors of the two studies said this was unlikely to be enough.