Global disaster is 30 years away, say climate scientists

The world has already burnt through two thirds of its “carbon budget” and must impose drastic cuts in emissions to avoid a catastrophic rise in temperature, a study has found.

The carbon budget is the maximum amount of greenhouse gas that scientists say can be emitted cumulatively since the industrial revolution to prevent the global average temperature rising more than 2C and threatening the lives of millions of people.

The remaining third of the budget will be exhausted within 30 years at the present rate of emissions, says the study in the journal Nature Geoscience.

The study comes as more than 100 world leaders, including David Cameron and Barack Obama, prepare to meet in New York tomorrow to renew their commitment to a global deal on cutting emissions, to be signed in Paris in December next year. However, hopes of ambitious pledges being made tomorrow have been undermined by the absence of the leaders of China and India, the world’s highest and third highest emitting nations.

China’s CO₂ emissions per person overtook those of the European Union last year, according to research by the University of East Anglia. China produced 7.2 tonnes of CO₂ per person in 2013, compared to the EU’s 6.8 tonnes. The US produced 16.5 tonnes per person; the global average was 5 tonnes.

Piers Forster, professor of physical climate change at the University of Leeds, said his “best guess” for the ten years to 2024 was that the average temperature would rise by 0.4C, twice as fast as in any previous decade.

Commenting on the study by 11 other senior climate scientists, he said it “gives us roughly 30 years until we pass the two degrees of warming threshold”.

He added: “Warming is currently around 0.8C since pre-industrial times. This means that over the next decades the world could be expected to warm by around 0.4C per decade — twice as fast as anything seen in the historical record.”

Professor Forster said the rate of global warming could “rebound” from the apparent pause since the 1990s, meaning the increase over the next decade could be even larger than 0.4C. Scientists have tried to explain the pause by suggesting that the oceans have temporarily absorbed some of the heat.

“If the world doesn’t warm as we expect, we climate scientists may have serious egg on our face. I would prefer that to be the case; but I fear the climate scientists may be right,” Professor Forster said.

The study said global CO₂ emissions had been rising by 2.5 per cent a year in the past decade. It concluded: “Stabilisation of global temperature rise at any level requires global carbon emissions to become eventually virtually zero.”

David Reay, professor of carbon management at the University of Edinburgh, said: “If this [study] were a bank statement, it would say our credit is running out. We’ve already burnt through two thirds of our global carbon allowance and avoiding dangerous climate change now requires some very difficult choices.”

Campaigners, including Emma Thompson, the actress, marched through central London yesterday to demand action on climate change.

Christiana Figueres, the UN official who co-ordinates the international climate change negotiations, has played down the prospects of the Paris deal involving a country-by-country allocation of a global carbon budget. Instead, the deal is likely to be based on voluntary emission reduction pledges from each country, based on a system of defining fair contributions yet to be agreed. She said: “Politically it would be very difficult.