(ESAS Bathymetric and Methane Emissions Map. Image source: Nature)
Arctic Methane emissions have been a touchy subject ever since sporadic reports began trickling in during the mid-2000s that volumes of the gas coming from local sources were on the rise. Two of the scientists producing these reports, Igor Semiletov and Natalia Shakova have been observing a key region of the Arctic called the East Siberian Arctic Shelf (ESAS) since the mid 1990s. At that time, Semiletov and Shakova found no major emissions sources coming from this vast sea whose bottom is composed primarily of carbon-rich submerged tundra.
That all changed in 2010 when an expedition led by Semiletov and Shakova discovered bubbling structures tens of meters across on the shallow and vulnerable ESAS sea bed. Returning in 2011, the pair were surprised and terrified by methane bubbling up from structures as large as 1 kilometer across. During this time Semiletov noted:
“Earlier we found torch-like structures like this but they were only tens of metres in diameter. This is the first time that we’ve found continuous, powerful and impressive seeping structures, more than 1,000 metres in diameter. It’s amazing. I was most impressed by the sheer scale and high density of the plumes. Over a relatively small area we found more than 100, but over a wider area there should be thousands of them.”
In the period of 2010 to 2013, other regions of the Arctic were also found to be emitting high volumes of both methane and CO2. These regions included but were not limited to Yedoma in Russia, other portions of the Siberian continental shelf, regions off of Svalbard, regions off of Greenland, and regions over Arctic Alaska and Canada (see NASA’s CARVE mission). Though the reports were sporadic and isolated, a picture began to emerge that the vast stores of Arctic carbon — totaling around 5,000 gigatons or a little less than ten times that already emitted via human fossil fuel burning — were beginning to contribute to the world’s atmospheric greenhouse gas stores.
Concern, especially over methane which creates between 25-75 times more warming than an equal volume of CO2, was on the rise. ESAS again fell into focus because about 1,500 gigatons of carbon in the form of methane is thought to be sealed under a now perforated and rapidly melting layer of permafrost. And by winter of 2013, satellite measures were showing an increasing overburden of methane in the atmosphere above the Arctic.
(You can view the 2009 to 2013 time series for January 21-31 below. Note the rapid increase in relative methane concentration. Click on image for higher resolution.)
(Image source: AQUA Satellite, NASA. Image produced by Dr. Leonid Yurganov)
These increasing methane levels were a sign of higher Arctic emissions. And, though concerning, they hadn’t yet risen to the level to indicate the catastrophic release that some scientists feared was possible.
By summer of 2013, Peter Wadhams, a polar researcher with more than 30 years experience studying Arctic sea ice from the vantage of British navy submarines, chimed in with an article published in the prestigious journal Nature entitled Climate science: Vast costs of Arctic change. In the article, Wadhams and his co-authors projected the economic costs of a catastrophic 50 gigaton methane emission from the East Siberian Arctic Shelf over the coming decades. Though the article itself didn’t provide an estimate of how likely such a dangerous emission would be, Wadhams, in his later press interviews indicated that he believed it was certainly possible due to new mechanisms set in motion by melting sea ice.
The Nature article received numerous criticisms from prominent climate modelers. Chief among these were David Archer and Gavin Schmidt. Archer and Schmidt both adhere to the notion that it will take centuries or perhaps thousands of years for a significant volume of methane to be emitted from the Arctic. They conjecture that emissions from Arctic sources will increase, but at a very slow rate, and to a level that is not markedly significant when compared to overall human CO2 emissions. This relatively slow and low Arctic contribution view is based on a model assessment of the physical sciences that has yet to quantify a strong enough physical mechanism to break methane out of its traps and produce the kind of emissions Wadhams and others fear.
In the conjecture over the potential dangers of Arctic methane release, Schmidt and Archer provide support for a long tail of emissions rather than a more sudden and powerful release.
To these criticisms, Wadhams responded in Cambridge University Press:
“What is happening is that the summer sea ice now retreats so far, and for so long each summer, that there is a substantial ice-free season over the Siberian shelf, sufficient for solar irradiance to warm the surface water by a significant amount – up to 7C according to satellite data. That warming extends the 50 m or so to the seabed because we are dealing with only a polar surface water layer here (over the shelves the Arctic Ocean structure is one-layer rather than three layers) and the surface warming is mixed down by wave-induced mixing because the extensive open water permits large fetches. So long as some ice persisted on the shelf, the water mass was held to about 0C in summer because any further heat content in the water column was used for melting the ice underside. But once the ice disappears, as it has done, the temperature of the water can rise significantly, and the heat content reaching the seabed can melt the frozen sediments at a rate that was never before possible.
The 2008 US Climate Change Science Program report needs to be seen in this context. Equally, David Archer’s 2010 comment that “so far no one has seen or proposed a mechanism to make that (a catastrophic methane release) happen” was not informed by the Semiletov/Shakhova field experiments and the mechanism described above. Carolyn Rupple’s review of 2011 equally does not reflect awareness of this new mechanism.”
It is worth noting that Dr. Wadhams has been very pessimistic about the state of the Arctic of late, predicting that a near complete loss of summer sea ice is likely by 2015 or 2016 — among the most rapid of such predictions. And the severe pessimism of one of the world’s premier sea ice researchers is not at all cause for comfort. This doesn’t mean that conditions are quite so bad as Wadhams suggests. But they could be. And this potential, along with the related potential for a more rapid ESAS release, is very unsettling, Archer’s and Schimdt’s reassurances aside.
Arctic no Longer in the Holocene
By October and November of 2013, the controversy over Wadhams Nature article had mostly faded. But with little in the way of new information, the details of the issue remained inconclusive as ever. Loss of Arctic sea ice had, at least, taken a pause. Sea ice area and extent had retrenched, under the continued assault of human warming, to levels last seen in 2009, but still remained near record low levels in all measures. This pause in the rate of loss was cause for some relief, if little comfort.
On the flip side, a new report had been issued showing that large regions of Arctic Canada were experiencing temperatures that were warmer than at any time in at least 44,000 years and probably 120,000 years. This report added to a long list of growing evidence that the Arctic was rapidly moving out of any reasonable context comparable to the Holocene and was probably well on its way toward something more closely resembling the Pliocene of about 3 million years ago (the last time CO2 levels hit 400 ppm) or worse.
And out of context, anomalous Arctic heat, meant out of context, anomalous stress on the ESAS’s frozen sea bed.
Arctic Methane Spikes as Shakhova Finds ESAS Emissions At Least Double Previous Estimates
Bad news was also coming from Arctic methane readings when, during September, October and November large spikes pushed local readings in some areas as high as 2500 parts per billion, more than a 600 parts per billion above the global average with large regions around the Arctic frequently showing readings above 1950 parts per billion.
By late November, another report had been issued by Shakhova and Semiletov. Published to the journal of Nature Geoscience, the report found that methane emissions from the East Siberian Arctic Shelf, one of the regions of greatest concern, was conservatively estimated to be about 17 megatons per year. This amount is twice that previously estimated by scientists, through the use of physical models and less refined observations, to be coming from this region. It also represents a total emission about twice that of the rest of the entire global ocean system.
The recent Shakhova paper also found the permafrost cap over the methane stored beneath the ESAS to be highly perforated and very close to thawing. Measurements taken from the permafrost showed the top layer had mostly already thawed while the still frozen layers lower down ranged in temperature between 30 and 32 degrees (Fahrenheit) — at the brink of melt. Furthermore, the composed data for the 1999 to 2013 period showed the seabed warming by .9 degrees Fahrenheit even as air temperatures warmed by 1.8 degrees (F) during the summer.
Increasing transport of warmer waters to ESAS bottom zones was facilitated by larger river outflows in the region, likely also a result of human-caused changes to Arctic weather patterns.
(ESAS bottom water temperature measurements from 1999 to 2012. Red = summer. Blue = winter. Green squares = historical data. Source: Nature)
Climate modelers had previously estimated it would take many hundreds of years, perhaps 5,000 to 7,000 years for ESAS permafrost to thaw under human warming. But Shakhova noted the models weren’t even accounting for the higher than estimated current rate of release:
“What we’re observing right now is much faster than what we anticipated and much faster than what was modeled,” Shakhova said. “We decided to be as conservative as possible. We’re actually talking the top of the iceberg.”
The methane beneath the ESAS was also found to be very responsive to environmental changes and conditions, no matter how transient or temporary. Storms, warming waters, and warmer ocean currents were observed to enhance release of methane from the ESAS. Yet one more sign of an increasingly fragile methane cap.
Models Wrong Again?
Anyone following the rapid pace of sea ice melt will recall how, up until very recently, sea ice melt models got the melt time frame dreadfully wrong. As recently as 2007, modellers were stating that near ice free conditions would not happen until the end of this century. Now, after two devastating record melt years in 2007 and 2012, bringing Arctic sea ice within a paltry 2.1 million square kilometers of zero, even the most conservative scientists project the potential for near ice free conditions by around 2035 to 2040, with the more aggressive among these putting the Arctic at a near ice-free end summer state by 2016 to 2020. Meanwhile, global climate model projections of sea ice loss continue to lag well behind observed trends. A mean of IPCC model runs still project a total or near total sea loss by 2100 in a mean of the models surveyed and those models that appear to be within the standard deviation of current observed ice loss trends predict, in their mean, an ice-free or near ice-free state by 2050. So what we have is a noted split between expert analysis of what is happening and what is likely happening to sea ice, and a continued set of highly conservative and apparently inaccurate (at least under current trends) projections by GCMs.
This observed conservatism in GCMs also calls into question their accuracy in predicting the response of global methane traps, especially the critical ESAS methane store. For the ESAS cap to even partly fail, as it now hints at doing, at any time this century would be another massive under-estimation by the climate models. It would also put at risk, as Wadhams warns, the release of gigatons of methane from its ever more permeable ESAS traps together with a number of very severe climate consequences.
Emission Rate Bad, But Not Catastrophic At This Time
Currently, however, it appears that such a very large release is not yet underway. A 17 megaton emission, though double previous estimates and outside the range projected by GCMs, represents about 2.8% of the global total methane emission from all sources (or 10% the total US emission). This puts ESAS on the map of very large single sources, but it does not yet provide enough methane to overwhelm the current methane balance. To do that, yearly rates would have to rise by an order of magnitude, reaching about 150 megatons a year or more.
Ironically, about a 150 megaton per year emission, averaged over thousands of years, is what climate models currently project (although the models show larger emissions happening much later). So it is worth noting that even getting on this track would be a bad consequence while exceeding it by any serious margin this century would be a very, very bad consequence indeed.
To put the size of the ESAS methane store into context it is worth considering that should the ESAS emit 1 gigaton of methane each year, it could continue that emission for more than a thousand years. Such a rate of emission would about effectively double the current forcing from human CO2 emissions and extend the time-frame of that forcing for up to 15 centuries.
Thankfully, we haven’t yet approached such a catastrophe. Instead, the current emission combines with other sources to continue to slowly push world methane levels higher, adding incrementally more heat forcing to an already stressed global system and adding to a yearly growth rate of about 10-20 ppb each year.
A Marker for Future Comparison
Shakhova’s research does, however, put a marker on the ESAS emissions map. Should we return in a few years to find emissions dramatically increased, we will have more evidence that ESAS is indeed rapidly destabilizing. Shakhova and Semiletov’s earlier observations provide some evidence for this already. However, with a quantifiable figure now available, it will be easier to gauge to what degree ESAS is increasing its already substantial, but not currently catastrophic, methane release.
(Updated December 18)