John Nissen: It may already be too late to deal with this terrifying leak

There are two critical problems: the rapid loss of sea ice and the emergence of methane from a thawing seabed

The shrinking of the Arctic sea-ice, in thickness and volume, has been considerably faster than predicted by the computer models used by the Intergovernmental Panel on Climate Change. As sea ice retreats, more ocean water is exposed, which is then heated to cause further retreat in what is known as a "positive-feedback loop".

Current projections by one team of Arctic scientists suggest that the sea ice in September, when it hits its summertime minimum, will all but have disappeared as early as 2015.

Outweighing this alarming state of affairs is the consequential rise in methane released from the Arctic seabed and surrounding tundra. The massive quantity of methane locked up in a frozen state in the Arctic presents a climate change "time bomb", with a fuse that is already burning.

The point of no return, when the positive feedback becomes unstoppable, could be very soon. It is now clear that there are two critical problems: the rapid loss of sea ice and the emergence of methane from a thawing seabed. They both call for rapid intervention to cool the region and to capture the methane.

John Nissen is chairman of the Arctic Methane Emergency Working Group