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.
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. In the past few days, researchers have seen areas of sea foaming with gas bubbling up through "methane chimneys" rising from the sea floor.
Many scientists fear the release of methane 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.
*Photo provided by Dave Cartier  under the Flickr creative commons license.