Scientists reframe carbon target debate

A new scientific study published today in Nature could serve to simplify the debate surrounding carbon targets, by warning that the world can only afford to burn another half a trillion tonnes of carbon if it is to prevent potentially catastrophic increases in average temperatures of more than 2°C.

The research calculated that the world has already burned about half a trillion tonnes of carbon since the industrial revolution, and that based on current projections it is on track to burn the next half a trillion tonnes within 40 years.

It warns that once a trillion tonnes of anthropogenic carbon has been burned, resulting in 3.67 trillion tonnes of carbon dioxide being released, global warming of between 1.6°C and 2.6°C is likely, with a rise of 2°C "most likely".

The EU has set a target of limiting average temperature rises to 2°C as scientists fear that larger increases in temperature could trigger the collapse of natural carbon sinks that would lead to still higher levels of carbon dioxide concentration in the atmosphere and result in "runaway climate change".

The new research suggests that a target based on how much carbon can still be burned would be simpler to understand and enforce than targets based on the rate of emissions or concentrations in the atmosphere, which have been adopted by many businesses and governments.

Writing in Nature, the research team, which was led by Oxford University's Myles Allen, said that "policy targets based on limiting cumulative emissions of carbon dioxide are likely to be more robust to scientific uncertainty than emission-rate or concentration targets".

The research implies that access to fossil fuels will eventually have to be blocked, warning that only a third of economically recoverable oil, gas and coal reserves can be burned before 2100 if two-degree warming is to be avoided.

The scientists said that while the research framed carbon targets in a different way to those being discussed as part of the UN's climate change talks, they were broadly in line with current expectations that global greenhouse gas emissions need to peak in about 2020.