The release of trapped greenhouse gases is pushing the world past the point of no return on climate change

The frozen bogs of Siberia are melting, and the thaw could have devastating consequences for the planet, scientists have discovered.

They have found that Arctic permafrost, which is starting to melt due to global warming, is releasing five times more methane gas than their calculations had predicted. That level of emission is alarming because methane itself is a greenhouse gas. Increased amounts will therefore accelerate warming, cause more melting of Siberian bogs and Arctic wasteland, and so release even more. 'It's a slow-motion time bomb,' said climate expert Professor Ted Schuur, of the University of Florida.

The discovery of these levels of methane release, revealed in a report in Nature last week, suggests that the planet is rapidly approaching a critical tipping point at which global warming could trigger an irreversible acceleration in climate change. 'The higher the temperature gets, the more permafrost we melt, the more tendency it has to become a more vicious cycle,' said Chris Field, director of global ecology at the Carnegie Institution of Washington. 'That's the thing that is scary about this.'

The news of the danger posed by rising methane levels comes after a week in which scientists outlined a series of disturbing developments in climate research. These disclosures included news that nearly every wild animal in Britain has extended its range northwards as the country heats up; ice cores from the Antarctic have revealed that carbon dioxide levels in the atmosphere are rising at an unprecedented rate; and analysis suggesting that the world has less than a decade in which to halt global warming before it reaches a point of no return.

The revelations about Siberia's methane add to these worries. Methane is produced in soil by bacterial decomposition and normally released into the air. However, in the permafrost regions of Siberia and the Arctic the gas gets locked into the frozen soil, and over the millennia this has built up to create a vast reservoir of the gas.

In addition to the methane built up, it is also known that vast amounts of carbon dioxide are locked in the planet's frozen zones. In total, it is estimated there could be as much as 450 billion tonnes of methane and carbon dioxide trapped in the world's permafrost.

A team led by Katey Walter of the University of Alaska decided to investigate the rate at which methane is being released as the world succumbs to the effects of climate change. She chose an area along the Kolyma river near Cherskii in Russia for the study.

The results revealed levels of discharge that were five times higher than previous estimates. The results, echoed by studies at 100 other sites in the north Siberia region, are alarming because methane is far more effective at trapping heat than carbon dioxide and is therefore potentially much more dangerous to the planet. Scientists have calculated that methane has a global warming potential that is 23 times that of carbon dioxide. This means that a kilogram of methane warms the planet's atmosphere 23 times as much as the same amount of carbon dioxide.

'The effects can be huge,' admitted Walter, adding: 'I don't think it can be easily stopped - we would have to have major cooling. It's coming out and there is a lot more to come out.'

Not just a wasteland

· Covering 10 million square kilometres, if Siberia were to secede from Russia it would be the world's largest country.

· Few people live there - only three people to every square kilometre -but it is rich in minerals, including gold and diamonds.

· The 9,295km Trans-Siberian Railway is the world's longest railway, running from Moscow to Vladivostok.

· The mammoth died out in Siberia 4,000 years ago, but frozen corpses are still being dug up.

· Tennis star Maria Sharapova and Rasputin were both born in Siberia