Scientists claim planet is heading for 'irreversible' climate change by 2040

The rise of greenhouse gases will trigger an unprecedented rate of global warming that will result in the loss of the ice-covered polar seas by 2020, much of our coral reefs by 2040 and see a 1.4-metre rise in the sea level by 2100.

The apocalyptic vision has been outlined in a paper by Andrew Brierley of St Andrews University, which is likely to influence the views of UN experts gathering in Copenhagen this December to establish a new protocol that will attempt to halt global warming.

Brierley and his co-author, Michael Kingsford of the James Cook University in Australia, examined the effect of carbon dioxide emissions on ocean habitats and marine organisms.

The scientists compared current carbon dioxide emissions with those forecast in 2007 by the Intergovernmental Panel of Climate Change (IPCC), the leading body for the assessment of global warming, which was established by the United Nations Environment Programme and the World Meteorological Organisation.

In 2007, the IPCC predicted a "worst-case scenario" that would see rapid industrialisation cause carbon dioxide in the atmosphere to increase by two parts per million each year. Parts per million (ppm) is a unit of concentration used to measure pollutants.

Brierley said atmospheric carbon dioxide concentration had increased from pre-industrial levels of 280 ppm to 385 ppm last year and was now rising at a rate of 2.5 ppm per year.

He described the outlook as "really quite nasty doom-and-gloom situation".

He added: "People have looked at how various economic situations, various developments in India and China might impact on carbon dioxide admissions and in 2007 they made a series of forecasts and if you take the worst-case scenario, carbon dioxide would be going up by two parts per million.

"This really august body, the Intergovernmental Panel on Climate Change, has said these are the worst-case scenarios for carbon dioxide increase and we are above that already. That's the thing that really frightens me."

In their paper, Brierley and Kingsford said that a carbon dioxide level of 450 ppm was the critical threshold beyond which catastrophic and irreversible change might occur.

Reaching that level would mean a global mean temperature rise of 2C above pre-industrial values. At present rates this threshold will be passed by 2040.

The authors added: "By 2040, some particularly sensitive marine ecosystems such as coral reefs and ice-covered polar seas could already have been lost and other unexpected consequences may arise."

Brierley said: "You can say no Arctic sea ice by 2020 – really, really soon. Certainly no summer sea ice in the Arctic by 2020."