The World Wide Fund for Nature (WWF) has just published a new report on climate change in the Arctic — Arctic Climate Feedbacks: Global Implications [PDF], and it’s a fascinating read. Over the last two years I’ve blogged regularly on the changes being seen in the Arctic — sea ice reductions, melting of the Greenland ice sheet, the danger of increased carbon release from permafrost and sea floor methane hydrates, and the possible impacts on northern hemisphere weather patterns and climate. WWF’s report — written by some of the leading names in the field (including Serreze, Stroeve, Cazenave, Rignot, Canadell, and for the methane hydrate chapter Shakhova and Semiletov) — pulls together all those strands to paint a picture of a region undergoing rapid change. The authors provide a fully-referenced review of our current understanding of the processes at work as the pole warms, with chapters covering atmospheric circulation feedbacks, ocean circulation changes, ice sheets and sea level, marine and land carbon cycle feedbacks, and sea floor methane hydrates. It’s compelling stuff, and well worth reading in full, but for this post I want to focus on the excellent overview of methane hydrate feedbacks provided by Natalia Shakhova and Igor Semiletov.
The methane hydrate chapter is the last in the report, but includes some of the more sobering information. It starts with an excellent primer on what methane hydrates are (methane molecules trapped in a lattice of ice crystals) and how they’re formed. The deposits on the floors of the shallow seas north of Siberia are particularly vulnerable — “extreme sensitivity to warming” is how the authors put it, and there’s an awful lot of methane up there:
…the arctic continental shelf […] is estimated to contain 2,500 gigatonnes of carbon in the form of methane hydrates, which is more than 3 times greater than the amount of carbon currently stored in the atmosphere and more than 600 times greater than the current atmospheric content of methane. Release to the atmosphere of only 0.5 per cent of the methane stored within arctic shelf hydrates could cause abrupt climate change.
The key to the stability of the hydrate deposits is the state of the permafrost “cap” that overlies them. This permafrost is much warmer than land-based permafrost because the ocean temperature is around freezing, whereas annual air temperatures over land in the region average around -17ÂºC. As ocean temperatures are rising (there have been “pulses” of warm water entering the Arctic Ocean over the last decade), the cap is becoming vulnerable. Just how vulnerable was news to me:
…recent observational data obtained in the East Siberian Arctic Shelf showed that extensive methane release from the seafloor is occurring at depths ranging from 6 to 70 metres, emerging as huge clouds of bubbles rising through the water column. This bubbling release of gas is called ebullition. […] In the East Siberian Arctic Shelf, which constitutes about 30 per cent of the entire Arctic shelf area, more than 50 per cent of the area studied is currently releasing methane to the atmosphere.
Methane released from deep sea deposits (such as the plumes off Spitsbergen discovered last year) dissolves in the sea water as it rises and is oxidised, but in shallower seas the gas reaches the atmosphere as bubbles. Over the ESS, atmospheric methane concentrations of up to 4 times normal levels have been measured in the last few years, and current methane release from Arctic hydrates could be as high as 10 to 50 million tonnes of methane per year. The situation in the ocean?
Multi-year observational data obtained in the East Siberian Arctic Shelf suggest that, contrary to modelling results, more than 80 per cent of bottom water and 50 per cent of surface water in the study area is supersaturated with methane by a factor of 10 to 1,000 relative to the background level of 3.5 nanomoles. That means that very likely more than 5 to 10 per cent of the East Siberian Arctic Shelf area is already affected by sub-sea permafrost destabilisation.
And what happens if a lot of methane is released?
Recent studies have examined two possible cases of how surface air temperature could respond to release of only 2 per cent (50 gigatonnes) of the total amount of methane preserved in arctic continental shelf hydrate deposits if this amount is released in either of two ways: slowly over 50 to 100 years, or quickly over approximately 5 to 10 years. When methane is released quickly over the brief 5 to 10 year time period, the maximum temperature increase is higher by about a factor of three compared to the â€œslowâ€ case. This greater temperature response is more likely to produce irreversible consequences.
Take that information, and feed it back into Chapter One of the report, where there’s a good discussion of how sea ice reductions spread winter warming onto the continents around the Arctic Ocean, and the potential for further positive feedback from permafrost becomes all too obvious. Carbon cycle feedbacks on that sort of scale have the potential to make any mitigation efforts we might undertake completely irrelevant. And that’s not good news.