Positive feedback

According to the IPCC's 2001 synthesis report, global warming is expected to increase global mean temperature by between 0.4 and 1.1 degrees by 2025, 0.8 to 2.6 degrees by 2050, and 1.4 to 5.8 degrees by 2100. This is expected to lead to significant climate change, resulting in decreased crop yields as agriculture struggles to adapt, threats to low-lying islands from increased sea-levels and storm surges, an increase in extreme weather events such as hurricanes and droughts, and an overall detrimental effect on human health due to poorer nutrition and increased incidence of tropical diseases such as Malaria. But more worrying is the risk of what the IPCC calls "large-scale, high-impact, non-linear and potentially abrupt changes in physical and biological systems". The shutting off of the Gulf Stream (the effects of which are shown in hyper-fast-forward in The Day After Tomorrow) is one such possibility - and one that already seems to be happening. The collapse of the West Antarctic ice sheet - which could raise sea-levels by 5 meters - is another. And now we have a new problem: the thawing of Siberia:

Researchers who have recently returned from the region found that an area of permafrost spanning a million square kilometres - 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.

Siberia is estimated to contain 70 billion tons of methane, a quarter of all stored in the ground. The release will be gradual, but will double the atmospheric concentration, and lead to a 10 to 25% increase in global warming. But what's most frightening is that this creates a positive feedback loop - the warmer it gets, the more methane is released, causing it to grow warmer still.

The report has already been confirmed by another group of researchers:

Katey Walter of the University of Alaska, Fairbanks, told a meeting of the Arctic Research Consortium of the US that her team had found methane hotspots in eastern Siberia. At the hotspots, methane was bubbling to the surface of the permafrost so quickly that it was preventing the surface from freezing over.

We may be in for a bumpy climate ride over the next century...