NASA scientist calls for stricter emission targets

Pressure on politicians to agree to far more demanding emission reduction targets than those currently being considered will increase today with the release of a new scientific study that claims the climate crisis is far more serious than currently thought.

The study from James Hansen, head of the Nasa Goddard Institute for Space Studies in New York, and eight other climate scientists is posted today on the Archive website and argues that the EU target of stabilising the amount of CO2 in the atmosphere at 550 parts per million (ppm) is grossly inadequate.

Speaking to The Guardian, Hansen said that CO2 levels should be slashed to 350ppm – a level below the current stock of greenhouse gasses in the atmosphere – if "humanity wishes to preserve a planet similar to that on which civilisation developed".

"If you leave us at 450ppm for long enough it will probably melt all the ice – that's a sea rise of 75 metres," he added. "What we have found is that the target we have all been aiming for is a disaster – a guaranteed disaster."

Hansen's team claim their research offers a more accurate assessment of the threat than recent reports from the Intergovernmental Panel on Climate Change as instead of using theoretical models it is based on core samples from the bottom of the ocean that provide evidence from the Earth's climatic history.

It also takes greater account of recent evidence showing the effect of so-called feedback mechanisms, such as the process whereby the melting of icecaps to be replaced by ocean reduces the albedo effect meaning more heat is absorbed and the ice retreats still faster.

The paper finds that if levels were allowed to reach 550ppm, the world would warm by 6C. In contrast, the research used to justify underpin the EU targets claims such a level would lead to an increase in temperatures of around 3C.

The scale of the emission reduction targets governments will have to achieve is the subject of intense debate. Both the proposed EU target to curb emissions by 20 per cent by 2020, rising to 30 per cent if other countries agree to similar goals, and the UK target to cut emissions by 60 per cent by 2050 are based on the assumption that "dangerous climate change" can be avoided if CO2 in the atmosphere is stabilised at between 450 and 550ppm.

These targets were supported by the Stern Review into the economics of climate change, which claimed that" stabilisation at 450ppm [the level Hansen claims will result in a 75 metre increase in sea levels] is already almost out of reach, given that we are likely to reach this level within ten years and that there are real difficulties of making the sharp reductions required with current and foreseeable technologies" .

However, a growing scientific consensus is building that far deeper cuts will be required. UK prime minister Gordon Brown responded to these fears last year with the promise of an independent review into whether the UK target should be increased to 80 per cent.

Now Hansen's study appears to suggest deeper cuts still and even raises the prospect of so called "carbon negative" measures whereby businesses and economies do not just reduce emissions to zero, but begin to actively remove carbon dioxide from the atmosphere through forestry programmes and currently undeveloped carbon scrubbing technologies.