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Huge quantities of methane below the Arctic seabed are showing signs of destabilising, according to research conducted in the East Siberian Sea. Scientists aboard Russian icebreakers have discovered that methane is leaking from the sub-sea permafrost far faster than had been previously estimated, raising concerns that climatic tipping points may have been reached.

As a greenhouse gas, methane is 25 times more powerful than carbon dioxide but emissions from subsea permafrost are not included in climate change prediction models. “The sub-sea permafrost should act as a cap or seal, preventing leakage,” Natalia Shakhova, of the University of Alaska. “Beneath it there is methane that has accumulated at high pressure.

But the permafrost is losing its ability to be an impermeable cap.” After water vapour and carbon dioxide, methane is the most significant of the gases that cause the atmosphere to retain heat. Levels have doubled since the beginning of the Industrial Revolution but 40 per cent of sources are natural, resulting from the decomposition of organic material in wetlands and other areas.

The permafrost that covers vast tracts of land in the far North is thawing, steadily adding methane to the atmosphere. The Arctic has warmed at about twice the rate of the rest of the planet. Climate scientists are concerned that as rising temperatures melt more permafrost, the added methane will raise temperatures further and so cause a wider thaw. Dr Shakhova said: “The climatic consequences of this are hard to predict.

This type of source has never been predicted by anyone and has not been included in climate models. We’re going to keep studying this region and investigating why this is happening. “Our concern is that the sub-sea permafrost has been showing signs of destabilisation already.” The permafrost covers the Siberian continental shelf, which extends up to 1,000 kilometres into the Arctic Ocean.

Dr Shakhova previously investigated methane releases from terrestrial permafrost and from northern lakes. Using Russian icebreakers to sample methane concentrations at various different water depths and above the surface at more than 5,000 locations, the team showed that methane was being released far faster than estimated.

They found that almost seven teragrams of methane, each equivalent to 1.1 billion tonnes of carbon, were being released every year from the East Siberian Arctic Shelf. A similar figure had previously been estimated to be the total for all world oceans. “This is a little alarming,” said Dr Shakhova. “We do not know how massive or sudden this outburst was.

We don’t know how many there were. We don’t know how close to the equilibrium we are. A lot of questions are still open.” Although difficult and expensive to conduct, surveys of oceanic methane production are crucial to the understanding of climatic tipping points.

According to the US Geological Survey, there may be twice as much carbon in the seabed as methane locked in ice, called methane hydrates, than that in known fossil fuel reserves. Only a combination of depth and temperature keeps them from being released.

Euan Nesbit, of Royal Holloway, University of London, said the work provided a vital baseline against which to gauge future changes. “This is an important marker point. Arctic methane emissions are clearly implicated in changes at the end of the last Ice Age, and they have shown that [methane from beneath oceanic permafrost] is a future risk from warming,” he said.

 
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