WHILE the world bickers over the extent and effects of climate change, an expanse of Arctic Ocean seabed is quietly bubbling methane into the air. It’s the first time that the ocean has been caught releasing this powerful greenhouse gas on such a scale.
The discovery will rekindle fears that global warming might be on the verge of unlocking billions of tonnes of methane from beneath the oceans, which could trigger runaway climate change. The trouble is, nobody knows if the Arctic emissions are new, or indeed anything to do with global warming.
Natalia Shakhova of the University of Alaska Fairbanks and colleagues collected 5000 samples of seawater over the East Siberian Arctic Shelf and measured the levels of methane at different depths. The team located more than 100 hotspots where methane is leaking from seabed permafrost; most of the water in the region had methane concentrations more than eight times the normal amount in the Arctic Ocean (Science, DOI: 10.1126/science.1182221).
The team calculate that the region is releasing about 7 million tonnes of the gas a year – about 2 per cent of overall methane emissions to the atmosphere, half of which result from human activity. But as the Arctic warms, it could release more and more. “Only a small fraction of the methane held in the ice shelf could trigger abrupt climate warming,” says Shakhova. As yet, it is not known whether the venting is an ongoing phenomenon or the start of a larger release.