The world is rapidly depleting its “carbon budget” for the first half of this century and must slash the carbon intensity of the global economy, a new report said recently.

Economists and climate change experts at PricewaterhouseCoopers (PwC) said their new research highlights the need for an ambitious carbon reduction agreement at the Copenhagen climate conference, which starts next week.

The report’s authors calculated the global carbon budget between 2000 and 2050 required to limit temperature rises to 2C, the climate threshold defined as “dangerous” by the EU.

A fifth of that budget had been used up by 2008, they said, meaning the world is already 10 per cent off the necessary trajectory to hit the target. The carbon “debt” in 2008 was equivalent to the joint emissions of the US and China.

John Hawksworth, PwC’s head of macroeconomics, said: “despite the widening consensus around the need to decarbonise, few countries are doing enough to live within our estimates of their carbon budgets. “If the world stays on this [course] we will have used up the entire global carbon budget for the first half of this century by 2034, 16 years ahead of schedule.”

The report added that the G20 countries which account for more than 80 per ecnt of global emissions need to cut their carbon intensity — the amount of carbon dioxide emitted for each unit of GDP — by 35 per cent by 2020, four times the rate achieved between 2000 and 2008.

Global emissions from the use of energy need to peak by 2015 and fall back to 2009 levels by the end of the next decade, the report said.

Leo Johnson, a PwC climate change partner, said previous inaction meant that much faster action was needed now: “If we had started on a low-carbon pathway in 2000, we would have needed to decarbonise at around 2 per cent a year up to 2008. We managed only 0.8 per cent in 2000-08.

“The result is we now need to decarbonise at a rate of 3.5 per cent a year to get back on track by 2020 — four times more than we have managed at the global level since 2000.”

The report said the EU, which claims leadership on the climate change agenda, is estimated to have been around 7 per cent off target in 2008, having improved carbon intensity by 1.8 per cent a year since 2000 compared to the 2.6 per cent annually that would have been necessary to be on target.

Only Russia reduced its carbon intensity by more than the budgeted amount since 2000, thanks to very rapid increases in energy efficiency, although it started from a very low base. — © Guardian Newspapers Limited, 2009