IFL Science has a report on the melting of the Siberian permafrost - The "Gateway To The Underworld" In Siberia Was Created By Climate Change.

The Independent has an article on melting permafroist in the Arctic and the methane being emitted as it melts - The methane time bomb.

The first evidence that millions of tons of a greenhouse gas 20 times more potent than carbon dioxide is being released into the atmosphere from beneath the Arctic seabed has been discovered by scientists.

The Independent has been passed details of preliminary findings suggesting that massive deposits of sub-sea methane are bubbling to the surface as the Arctic region becomes warmer and its ice retreats.

Underground stores of methane are important because scientists believe their sudden release has in the past been responsible for rapid increases in global temperatures, dramatic changes to the climate, and even the mass extinction of species. Scientists aboard a research ship that has sailed the entire length of Russia's northern coast have discovered intense concentrations of methane – sometimes at up to 100 times background levels – over several areas covering thousands of square miles of the Siberian continental shelf.

In the past few days, the researchers have seen areas of sea foaming with gas bubbling up through "methane chimneys" rising from the sea floor. They believe that the sub-sea layer of permafrost, which has acted like a "lid" to prevent the gas from escaping, has melted away to allow methane to rise from underground deposits formed before the last ice age.

They have warned that this is likely to be linked with the rapid warming that the region has experienced in recent years.

Methane is about 20 times more powerful as a greenhouse gas than carbon dioxide and many scientists fear that its release could accelerate global warming in a giant positive feedback where more atmospheric methane causes higher temperatures, leading to further permafrost melting and the release of yet more methane.

The amount of methane stored beneath the Arctic is calculated to be greater than the total amount of carbon locked up in global coal reserves so there is intense interest in the stability of these deposits as the region warms at a faster rate than other places on earth. ...

The Arctic region as a whole has seen a 4C rise in average temperatures over recent decades and a dramatic decline in the area of the Arctic Ocean covered by summer sea ice. Many scientists fear that the loss of sea ice could accelerate the warming trend because open ocean soaks up more heat from the sun than the reflective surface of an ice-covered sea.