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Reposting from last year
Arctic
Methane Monster Shortens Tail: Shakova, Semiletov Study Shows ESAS
Emitting Methane at Twice Expected Rate
12 December, 2013
(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.
Misplaced
Mechanisms
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.
“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.
Links:
(Updated
December 18)
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