Abstract link 
http://m.sciencemag.org/content/early/2013/02/20/science.1228729.abstract?sid=d26b1542-62e0-4aa0-9239-a82abda2d1ad

Major methane release is almost inevitable

19:00 21 February 2013 by Michael Marshall

We are on the cusp of a tipping point in the climate. If the global 
climate warms another few tenths of a degree, a large expanse of the 
Siberian permafrost will start to melt uncontrollably. The result: a 
significant amount of extra greenhouse gases released into the 
atmosphere, and a threat – ironically – to the infrastructure that 
carries natural gas from Russia to Europe.The Arctic is warming faster 
than the rest of the planet, and climatologists have long warned that 
this will cause positive feedbacks that will speed up climate change 
further. The region is home to enormous stores of organic carbon, mostly 
in the form of permafrost soils and icy clathrates that trap methane – a 
powerful greenhouse gas that could escape into the atmosphere.The 
Siberian permafrost is a particular danger. A large region called the 
Yedoma could undergo runaway decomposition once it starts to melt, 
because microbes in the soil would eat the carbon and produce heat, 
melting more soil and releasing ever more greenhouse gases. In short, 
the melting of Yedoma is a tipping point: once it starts, there may be 
no stopping it.For the first time, we have an indication of when this 
could start happening. Anton Vaks of the University of Oxford in the UK 
and colleagues have reconstructed the history of the Siberian permafrost 
going back 500,000 years. We already know how global temperatures have 
risen and fallen as ice sheets have advanced and retreated, so Vaks's 
team's record of changing permafrost gives an indication of how 
sensitive it is to changing temperatures.

Stalagmite record

But there is no direct record of how the permafrost has changed, so Vaks 
had to find an indirect method. His team visited six caves that run 
along a south-north line, with the two southernmost ones being under the 
Gobi desert. Further north, three caves sit beneath a landscape of 
sporadic patches of permafrost, and the northernmost cave is right at 
the edge of Siberia's continuous permafrost zone.The team focused on the 
500,000-year history of stalagmites and similar rock formations in the 
caves. "Stalagmites only grow when water flows into caves," Vaks says. 
"It cannot happen when the soil is frozen." The team used radiometric 
dating to determine how old the stalagmites were. By building up a 
record of when they grew, Vaks could figure out when the ground above 
the caves was frozen and when it wasn't.As expected, in most of the 
caves, stalagmites formed during every warm interglacial period as the 
patchy permafrost melted overhead.But it took a particularly warm 
interglacial, from 424,000 and 374,000 years ago, for the stalagmites in 
the northernmost cave to grow – suggesting the continuous permafrost 
overhead melted just once in the last 500,000 years.At the time, global 
temperatures were 1.5 °C warmer than they have been in the last 10,000 
years. In other words, today's permafrost is likely to become vulnerable 
when we hit 1.5 °C of global warming, says Vaks."Up until this point, we 
didn't have direct evidence of how this happened in past warming 
periods," says Ted Schuur of the University of Florida in Gainesville.It 
will be very hard to stop the permafrost degrading as a warming of 
1.5 °C is not far off. Between 1850 and 2005, global temperatures rose 
0.8 °C, according to the 2007 report of the Intergovernmental Panel on 
Climate Change. Even if humanity stopped emitting greenhouse gases 
tomorrow, temperatures would rise another 0.2 °C over the next 20 years. 
That would leave a window of 0.5 °C – but in fact our emissions are 
increasing. What's more, new fossil fuel power stations commit us to 
several decades of emissions.

Soggy permafrost

What are the consequences? The greatest concern, says Tim Lenton of the 
University of Exeter in the UK, is the regional landscape. Buildings and 
infrastructure are often built on hard permafrost, and will start 
subsiding. "Ice roads won't exist any more."The increasingly soggy 
permafrost will also threaten the pipelines that transport Russian gas 
to Europe. "The maintenance and upkeep of that infrastructure is going 
to cost a lot more," says Schuur.As for the methane that could be 
released into the atmosphere, Schuur estimates that emissions will be 
equivalent to between 160 and 290 billion tonnes of carbon dioxide.That 
sounds like a lot, but is little compared to the vast amount humans are 
likely to emit, says Lenton. "The signal's going to be swamped by fossil 
fuel [emissions]."He says the dangers of the permafrost greenhouse gases 
have been overhyped, particularly as much of the methane will 
be converted to carbon dioxide by microbes in the soil, leading to a 
slower warming effect.Schurr agrees with Lenton that the methane 
emissions are "not a runaway effect but an additional source that is not 
accounted in current climate models".Journal reference: Science, DOI: 
10.1126/science.1228729