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`Tipping point' in Siberia may spur global warming

A vast expanse of western Siberia is undergoing an unprecedented thaw that could dramatically increase the rate of global warming, climate scientists warned yesterday.

Researchers who have recently returned from the region found that an area of permafrost spanning 1 million km2 -- the size of France and Germany combined -- has started to melt for the first time since it formed 11,000 years ago at the end of the last ice age.

The area, which covers the entire sub-Arctic region of western Siberia, is the world's largest frozen peat bog and scientists fear that, as it thaws, it will release billions of tonnes of methane, a greenhouse gas 20 times more potent than carbon dioxide, into the atmosphere.

It is a scenario climate scientists have feared since first identifying "tipping points" -- delicate thresholds where a slight rise in the Earth's temperature can cause a dramatic change in the environment that itself triggers a far greater hike in global temperatures.

The discovery was made by Sergei Kirpotin at Tomsk State University in western Siberia and Judith Marquand at Oxford University and was reported in New Scientist yesterday.

The researchers found that what was until recently a barren expanse of frozen peat is turning into a broken landscape of mud and lakes, some more than 1km across.

Kirpotin told the magazine the situation was an "ecological landslide that is probably irreversible and is undoubtedly connected to climatic warming."

He added that the thaw had probably begun in the past three or four years.

Climate scientists yesterday reacted with alarm to the finding, and warned that predictions of future global temperatures would have to be revised upwards.

"When you start messing around with these natural systems, you can end up in situations where it's unstoppable. There are no brakes you can apply," said David Viner, a scientist at the Climatic Research Unit at the University of East Anglia. "This is a big deal because you can't put the permafrost back once it's gone. The causal effect is human activity and it will ramp up temperatures even more than our emissions are doing."

Scientists are particularly concerned about the permafrost because as it thaws, it reveals bare ground which warms up more quickly than ice and snow, and so accelerates the rate at which the permafrost thaws.

The permafrost is likely to take many decades at least to thaw, so the methane locked within it will not be released into the atmosphere in one burst, said Stephen Sitch, a scientist at the Met Office's Hadley Centre in Exeter.

But calculations by Sitch and his colleagues show that even if methane seeped from the permafrost over the next 100 years, it would add around 700 million tonnes of carbon into the atmosphere each year, roughly the same amount that is released annually from the world's wetlands and agriculture. It would effectively double atmospheric levels of the gas, leading to a 10 percent to 25 percent increase in global warming, he said.
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