Seven facts you need to
know about the Arctic methane timebomb
Dismissals of catastrophic methane danger ignore robust science in favour of outdated mythology of climate safety
Melting ice in the Arctic. Photograph:
Getty
Nafeez Ahmed : Mon 5 Aug 2013 06.01 BST
Debate over the plausibility of a
catastrophic release of methane in coming decades due to thawing Arctic
permafrost has escalated after a new Nature paper warned that exactly this
scenario could trigger costs equivalent to the annual GDP of the global
economy.
Scientists of different persuasions
remain fundamentally divided over whether such a scenario is even plausible.
Carolyn Rupple of the US Geological Survey (USGS) Gas Hydrates Project
told NBC News the scenario is "nearly
impossible." Ed Dlugokencky, a research scientist at the National Oceanic
and Atmospheric Administration's (NOAA) said there has been "no detectable
change in Arctic methane emissions over the past two decades." NASA's
Gavin Schmidt said that ice core records from previously warm Arctic periods
show no indication of such a scenario having ever occurred. Methane hydrate
expert Prof David Archer reiterated that "the mechanisms for release
operate on time scales of centuries and longer." These arguments were
finally distilled in a lengthy, seemingly compelling essay posted on Skeptical Science last Thursday, concluding with
utter finality:
"There
is no evidence that methane will run out of control and initiate any sudden,
catastrophic effects."
But none of the scientists rejecting
the plausibility of the scenario are experts in the Arctic,
specifically the East Siberia Arctic Shelf (ESAS). In contrast, an emerging
consensus among ESAS specialists based on continuing fieldwork is highlighting
a real danger of unprecedented quantities of methane venting due to thawing
permafrost.
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So who's right? What are these Arctic
specialists saying? Are their claims of a potentially catastrophic methane
release plausible at all? I took a dive into the scientific literature to find
out.
What I discovered was that Skeptical
Science's unusually skewered analysis was extremely selective, and focused
almost exclusively on the narrow arguments of scientists out of touch with
cutting edge developments in the Arctic. Here's what you need to know.
1. The 50 Gigatonne decadal methane
pulse scenario was posited by four Arctic specialists, and is considered
plausible by Met Office scientists
The authors of the controversial new
Nature paper on costs of Arctic warming didn't just pull their
decadal methane catastrophe scenario out of thin air. The scenario was first postulated in 2008 by Dr Natalie Shakhova of
the University of Alaska Fairbanks, Dr Igor Semiletov from the Pacific
Oceanological Institute at the Russian Academy of Sciences, and two other
Russian experts.
Their paper noted that while seabed
permafrost underlaying most of the ESAS was previously believed to act as an
"impermeable lid preventing methane escape," new data showing
"extreme methane supersaturation of surface water, implying high
sea-to-air fluxes" challenged this assumption. Data showed:
"Extremely
high concentrations of methane (up to 8 ppm) in the atmospheric layer above the
sea surface along with anomalously high concentrations of dissolved methane in
the water column (up to 560 nM, or 12000% of super saturation)."
One source of these emissions
"may be highly potential and extremely mobile shallow methane hydrates,
whose stability zone is seabed permafrost-related and could be disturbed upon
permafrost development, degradation, and thawing." Even if the methane
hydrates are deep, fissures, taliks and other soft spots create heat pathways from the seabed which warms quickly
due to shallow depths. Various mechanisms for such processes have been elaborated
in detail.
The paper then posits the
plausibility of a 50 Gigatonne (Gt) methane release occurring abruptly "at
any time." Noting that the total quantity of carbon in the ESAS is
"not less than 1,400 Gt", the authors wrote:
"Since
the area of geological disjunctives (fault zones, tectonically and seismically
active areas) within the Siberian Arctic shelf composes not less than 1-2% of
the total area and area of open taliks (area of melt through permafrost),
acting as a pathway for methane escape within the Siberian Arctic shelf reaches
up to 5-10% of the total area, we consider release of up to 50 Gt of predicted
amount of hydrate storage as highly possible for abrupt release at any time.
That may cause ∼12-times increase of modern
atmospheric methane burden with consequent catastrophic greenhouse
warming."
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So the 50 Gt scenario used by the new
Nature paper does not postulate the total release of the ESAS methane hydrate
reservoir, but only a tiny fraction of it.
The scale of this scenario is roughly
corroborated elsewhere. A 2010 scientific analysis led by the UK's Met Office in
Review of Geophysics recognised the plausibility of catastrophic carbon
releases from Arctic permafrost thawing of between 50-100 Gt this century, with
a 40 Gt carbon release from the Siberian Yedoma region possible over four
decades.
Shakhova and her team have developed
these findings from data derived from over 20
field expeditions from 1999 to 2011. In 2010, Shakhova et. al
published a paper in Science based on their annual research
trips which highlighted that the ESAS was a key reservoir of
methane "more than three times as large as the nearby Siberian wetland...
considered the primary Northern Hemisphere source of atmospheric methane."
Current average methane concentrations in the Arctic are:
"about
1.85 parts per million, the highest in 400,000 years" and "on par
with previous estimates of methane venting from the entire World Ocean."
As the ESAS is shallow at only 50
metres, most of the methane being released is escaping into the atmosphere rather
than being absorbed into water.
The existence of such shallow methane
hydrates in permafrost - at depths as small as 20m - was
confirmed by Shakhova in the Journal of Geophysical Research. There has been direct observation and sampling of these hydrates by Russian geologists in recent decades until now; this has also been
confirmed by US government scientists.
2. Arctic methane hydrates are
becoming increasingly unstable in the context of anthropogenic climate change
and it's impact on diminishing sea ice
The instability of Arctic methane
hydrates in relation to sea ice retreat - not predicted by conventional
models - has been increasingly recognised by experts. In 2007, a study in Eos, Transactions found that:
"Large
volumes of methane in gas hydrate form can be stored within or below the subsea
permafrost, and the stability of this gas hydrate zone is sustained by the
existence of permafrost. Degradation of subsea permafrost and the consequent
destabilization of gas hydrates could significantly if not dramatically
increase the flux of methane, a potent greenhouse gas, to the atmosphere."
In 2009, a research team of 19
scientists wrote a paper in Geophysical Research Letters documenting
how the past thirty years of a warming Arctic current due to contemporary
climate change was triggering unprecedented emissions of methane from gas
hydrate in submarine sediments beneath the seabed in the West Spitsbergen
continental margin. Prior to the new warming, these methane hydrates had
been stable at water depths as shallow as 360m. Over
250 plumes of methane gas bubbles were found rising from the seabed due to the
1C temperature increase in the current:
"...
causing the liberation of methane from decomposing hydrate... If this process
becomes widespread along Arctic continental margins, tens of Teragrams of
methane per year could be released into the ocean."
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The Russian scientists investigating
the ESAS also confirmed that the levels of methane release they
discovered were new. As Steve Connor reported in the Independent,
since 1994 Igor Semilitov:
"...
has led about 10 expeditions in the Laptev Sea but during the 1990s he did not
detect any elevated levels of methane. However, since 2003 he reported a rising
number of methane 'hotspots', which have now been confirmed using more
sensitive instruments."
In 2012, a Nature study mapping over 150,000 Arctic methane
seeps concluded that:
"...
in a warming climate, disintegration of permafrost, glaciers and parts of the
polar ice sheets could facilitate the transient expulsion of 14C-depleted
methane trapped by the cryosphere cap."
3. Multiple scientific reviews,
including one by over 20 Arctic specialists, confirm decadal catastrophic
Arctic methane release is plausible
A widely cited 2011 Nature review dismissed such a catastrophic
scenario as implausible because methane "gas hydrates occur at low
saturations and in sediments at such great depths below the seafloor or onshore
permafrost that they will barely be affected by [contemporary levels of]
warming over even [1,000] yr."
But this study and others like it
completely ignore the new empirical evidence on permafrost-associated shallow
water methane hydrates on the Arctic shelf. Scientific reviews that have
accounted for the empirically-observed dynamics of permafrost-associated
methane come to the opposite conclusion.
In 2007, scientists Matthew Reagan
and George Moridis at the Lawrence Berkeley National Laboratory published a paper in Geophysical Research Letters exploring
the vulnerability of methane gas hydrates. They concluded based on simulations
of different types of oceanic gas hydrate responding to seafloor temperature
changes:
"...
while many deep hydrate deposits are indeed stable under the influence of rapid
seafloor temperature variations, shallow deposits, such as those
found in arctic regions or in the Gulf of Mexico, can undergo rapid dissociation and produce significant carbon
fluxes over a period of decades."
A 2010 scientific analysis led by the UK's Met Office in Review of
Geophysics found:
"The
time scales for destabilization of marine hydrates are not well understood and
are likely to be very long for hydrates found in deep sediments but much shorter for hydrates below shallow waters, such as in the
Arctic Ocean... Overall, uncertainties are large, and it is
difficult to be conclusive about the time scales and magnitudes of methane
feedbacks, but significant increases in methane emissions are
likely, and catastrophic emissions cannot be ruled out... The risk of a rapid increase in [methane] emissions is real but
remains largely unquantified."
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Another extensive scientific review
of data from the ESAS gathered between 1995 and 2011 by over twenty Arctic
specialists published in the Proceedings of the Russian Academy of Sciences similarly
concluded that:
"The
[ESAS] is a powerful supplier of methane to the atmosphere owing to the
continued degradation of the submarine permafrost, which causes the destruction
of gas hydrates. The emission of methane in several areas of
the [ESAS] is massive to the extent that growth in the methane concentrations
in the atmosphere to values capable of causing a considerable and even catastrophic
warning on the Earth is possible."
Other recent scientific reviews corroborate these findings.
4. Current Arctic methane levels are
unprecedented
A 2011 Nature paper found that ten times more carbon
than thought is escaping via thawing coastal permafrost at the ESAS. Although
it is not yet clear whether or how the quantities of Arctic methane are
impacting on total atmospheric methane emissions, a number of scientists argue
that the increasing spikes in methane detected in the Arctic in recent years is
indeed unprecedented.
Despite NOAA scientist Dr Dlugokencky's reassurances that current
Arctic methane emission levels are nothing to be "alarmed" about, his
own data shows that Arctic methane levels were 1850 ppb in yr 2000, rising up
to 1890 ppb in 2012.
Indeed, Dr Leonid Yurganov, Senior
Research Scientist at the NASA/UMBC Joint Centre for Earth Systems Technology,
and his co-scientists from NOAA and Harvard (Shawn Xiong and Steven Wofsy)
disagree with Dlugokencky. In a paper for the American Geophysical Union last
December they charted a worrying "global increase of methane" since
2007-8, with particular spikes in 2009 and 2011-12 in the northern hemisphere,
with maximum methane concentrations in the Arctic:
"IASI
data for the autumn months (October-November) clearly indicate Eurasian shelf
areas of the Arctic Ocean as a significant methane emitter. The maximal methane
concentrations were found over Kara and Laptev Seas. According to IASI data,
during the last three years in autumn time, methane over Eurasian shelf has
been increased by 25 ppb, over the N. American shelf, by 23 ppb, and over the
land between 50 N and 70 N for both Eastern and Western hemispheres, by 20
ppb."
Yurganov et. al point out that
between January 2009 and 2013, Arctic methane levels ramped steadily higher by
about 10-20 ppb on average each year. They also note that maximum Arctic
methane emissions occur annually between September and October - coinciding
with the Arctic sea ice minimum.
5. The tipping point for continuous
Siberian permafrost thaw could be as low as 1.5C
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New research led by Prof Antony Vaks
published this year in Science analysing a 500,000 year
history of Siberian permafrost found that "global climates only slightly
warmer than today are sufficient to thaw significant regions of
permafrost." The study by eight experts found that there is a tipping
point for continuous thawing of permafrost at 1.5C which "can potentially
lead to substantial release of carbon trapped in the permafrost into the
atmosphere."
6. Arctic conditions during the
Eemian interglacial lasting from 130,000 to 115,000 years ago are a terrible
analogy for today's Arctic
Two recent studies challenge the
relevance of Arctic conditions in the Eemian interglacial. A 2012 Geophysical
Research Letters study rejects the idea that the Arctic experienced ice free
summers in the Eemian, noting that Arctic temperatures were cooler than previously thought, with evidence that ice
sheets were more resistant - partly due to vastly different Arctic ocean
currents. Similarly, a new Nature study found that the Greenland ice
sheets experienced only modest melting in the Eemian, such that the extensive
sea level rise at the time could only be explained by melting in Antarctica. Both studies suggest that the
Arctic sea ice simply had not retreated enough to expose permafrost.
According to Prof Paul Beckwith of
the University of Ottawa Laboratory for Paleoclimatology and Climatology, this
can be explained by a number of factors:
"...
the key distinction is that the warming today is from Greenhouse gases being
higher and occurs 'twenty-four seven', namely the cooling at night is much less
(diurnal variation smaller); in the Eemian the tilt of the Earth was much
greater so there was much more seasonality, thus winters were much colder so
the sea ice extent, thickness, and thus volume could build up much more, and
the summers were warmer in the daytime, however the cooling at night was much
greater than now (less greenhouse gas [GHG], more diurnal variation); net
result is that the ice was much more durable in the Eemian. Greenland temps
were higher during the daytime, but cooled off much more during the nighttime
in the lower GHG concentration world."
7. Paleoclimate records will not
necessarily capture a large, abrupt methane pulse
Prof Beckwith also poured (ice cold)
water on the claim that we know an abrupt methane release cannot occur, because
it has never occurred before - purportedly proven as such an event is not
detected in the ice cores:
"The
length of time for the methane pulse is very important here. If most of the
methane came out in a decade, for example then within a subsequent decade or so
most of the methane will have been broken down to CO2 and H20 and also been
dispersed/distributed around the planet, away from the pulse source area in the
Arctic. The CO2 produced would have been small (CO2 stayed within 180-280 ppm
range). It takes about 50 years or even more (depending on the snowfall rate
and surface melt rates) for snow at the surface to be compacted into firn that
closes off the air spaces creating the bubbles in the ice that are reservoirs of
the methane and other atmospheric gases. Because of that 50 year bubble closure
time, the large pulse of methane that was burped out of the marine sediments
and terrestrial permafrost would be long gone and not result in a detectable
signal in the ice core record. Just because the record does not capture it does
not mean that it was not produced."
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These comments are confirmed by an
in-depth American Geophysical Union study which notes that
it "remains unclear if the full magnitude of atmospheric [methane] changes
are recorded in ice cores because of diffusional smoothing of the [methane]
while in the firn" as well as "signal smoothing" caused by
"atmospheric effects."
But studies do indicate past
precedent. A 2009 Science paper argues that abrupt,
catastrophic emissions from Arctic methane clathrates including from thawing
permafrost played a key role 11,600 years ago at the end of the Younger Dryas
cold period in driving wetland emissions, generating sudden massive warming.
So what?
All this proves that the $60 trillion
price-tag for Arctic warming estimated by the latest Nature commentary should
be taken seriously, prompting further urgent research and action on mitigation
- rather than denounced on the basis of outdated, ostrich-like objections based
on literature unacquainted with the ESAS.
Dr Nafeez Ahmed is executive director of the Institute for Policy Research & Development and author of A User's Guide to the Crisis of Civilisation: And How to Save It among other books. Follow him on Twitter @nafeezahmed
