Thaw will speed warming

Siberia's peatbogs have been churning out methane for 11,000 years but billions of tonnes of the gas has remained locked within the permafrost that covers it.

Because the permafrost is coated in snow and ice, it reflects sunlight before it can be warmed up.

But in recent decades, as the temperature of the globe has risen, the vast expanse of western Siberia has begun a slow thaw.

The melting of the permafrost is more than a mere indication of climate change. It is an example of a finely balanced environmental system that when upset by global warming can trigger a dramatic reaction that drives global temperatures up further.

If the permafrost thaws and the meltwater drains away, the bogs will dry out, leaving the methane to oxidise into carbon dioxide and escape into the atmosphere.

If the bogs stay wet, as is the case for most in the region, the gas will bubble up as methane. Because methane can absorb more heat than carbon dioxide, it is a far more potent greenhouse gas and contributes more to global warming.

Some scientists estimate that the vast west Siberian peatbog holds around 70bn tonnes of methane.

Climate scientists fear that as the Siberian permafrost and similar "tipping points" around the world are triggered by warming, they will cause knock-on effects that make temperatures around the world rise faster and faster, leading to runaway global warming that could have devastating consequences for the world's economy and environment.

Scientists only identified such delicate, but potentially devastating, environmental systems in the past five years or so and because current models do not take them into account, it is highly likely that estimates of future warming will have to be revised upwards.