More than 250 plumes of the gas are rising from the seafloor west of the Norwegian archipelago of Svalbard, according to the joint British–German research team.

The gas is normally trapped in sediment within the crystal structure of an ice-like substance known as methane hydrate, which is stable only within a narrow temperature range. The West Spitsbergen current, which flows past the islands, has warmed by 1°C in the past 30 years, destabilising the hydrate and releasing the gas.

Although similar plumes have been found in the Black Sea and the Gulf of Mexico, this is the first time that such releases have been attributed to global warming.

Graham Westbrook of the University of Birmingham, who led the study, said: ‘If this process becomes widespread along Arctic continental margins, tens of megatonnes of methane a year could be released into the ocean.’

Methane is 20 times as potent a greenhouse gas as carbon dioxide, but the scientists found no evidence that the plumes were breaking the water’s surface and entering the atmosphere, although they believe that larger plumes could potentially do so. However, methane reacts with oxygen in seawater to form CO2, which, in turn, creates carbonic acid, which contributes to ocean acidification.

October 2009