Toward
Genuinely Improved Discussions of Methane & Climate
9
August, 2013
The
post 'Toward Improved Discussions of Methane & Climate' recently
appeared atSkepticalScience,
in response to the recent publication in Nature of 'Vast
Costs of Arctic Change',
by Gail Whiteman, Chris Hope, and Peter Wadhams.
Below
are Paul Beckwith's comments that were recently submitted at
that post but SkepticalScience refused them to be posted.
The text by SkepticalScience is in italics. Paul's comments are in
red.
SkepticalScience: “Here
at Skeptical Science, there is an ongoing effort to combat
disinformation from those who maintain that climate change is a
non-issue or non-reality. From time to time, however, individuals or
groups overhype the impacts of climate change beyond the realm of
plausibility. Some of this is well-intentioned but misguided. For
those who advocate climate literacy or for scientists who engage with
the public, it is necessary to call out this stuff in the same manner
as one would call out a scientist who doesn’t think that the modern
CO2 rise is due to human activities.
Many
overblown scenarios or catastrophes seem to involve methane in the
Arctic in some way. There are even groups
out there declaring
a planet-wide emergency because of catastrophic, runaway feedbacks,
involving the interplay between high latitude methane sources and sea
ice.”
Paul
Beckwith: The above two paragraphs set the tone of this discourse.
AMEG (Arctic Methane Emergency Group) is unjustly framed in this
introduction as a fringe group using such terms as “overhype”,
“beyond realm of plausibility”, “overblown scenarios or
catastrophes”, “planet-wide emergency”. This is the complete
opposite of the truth. AMEG was founded based on a meeting in
October, 2011 in the U.K. and I joined in December, 2011. We are a
group of concerned professionals with a varied background including
climate scientists, engineers, doctors, moviemakers, economists,
journalists.
We
have studied the Arctic, methane, sea ice, and climate change as a
group since that time, and individually for much longer. We base our
work and analysis on observations, not on models.
The
facts on the ground and ocean in the Arctic region speak for
themselves. The PIOMAS work, which has been substantiated
independently by CryoSat satellite data, show that the sea ice volume
is trending downwards exponentially and if that trend continued would
reach zero around 2015 or 2016. Trending down even faster is the May
and June Arctic snow cover, as measured clearly by Rutgers data.
Methane levels in the Arctic have increased significantly over the
last several years. In fact, the mainstream scientific viewpoint was
that the seafloor over the ESAS (Eastern Siberia Arctic Shelf) was
impermeable to methane outgassing. Then Shakhova, Yurganov, and other
Russian scientists measured outgassing plumes tens of meters in
diameter one year expanding to kilometers in diameter the very next
year. Flask measurements in Barrow, Alaska and Svalbaard indicated
local levels of >2100 ppb and AIRS satellite measurements over the
last decade have shown greatly increase levels of methane in the last
few years. This is all observation, and not modeled by anybody. In
fact, higher methane emissions have been reported along the Arctic
coastlines, presumably from enhanced wave action due to larger wave
action from the increased ice-free ocean.
Also,
higher emissions have been measured elsewhere from continental
shelves, for example off the east coast of North America from warm
Gulf Stream water that has shifted eastward over the shelves, warming
ocean temperatures several degrees.
Thus,
the “radical” or “fringe” or “out-there” view is not from
AMEG, quite the opposite. Based on the precautionary principle, it is
imperative that so called “mainstream” science examine this data
without preconceptions that it takes centuries or millennia for
methane to outgas. It is unfathomable to AMEG and many others that
main-stream science are behaving like “methane denialists” when
the observations are clearly undermining such out-of-hand rejection,
based on inaccurate models that are clearly missing feedbacks. In
fact the situation is so ridiculous that the IPCC is not even
considering methane as a strong feedback in their next report.
People
on the street are now recognizing that the weather extremes are
moving off the charts in terms of frequency, severity, and spatial
extent (mostly for extensive long duration droughts, and also
torrential rains causing floods). They are starting to recognize that
the collapse in Arctic albedo from declining snow cover and sea ice
loss is greatly amplifying the warming in the Arctic. This obviously
lowers the temperature gradient between the equator and North Pole
which via simple physical laws slows the jet streams making them
wavier and stickier. This changing global circulation, combined with
4% higher water vapor in the atmosphere is causing these weather
extremes.
Things
are happening that have never been observed before in human history.
Like the rate of decline of sea ice and snow cover, the extensive
cracking of sea ice this March-2013, the “hole” forming near the
north pole from relatively weak cyclones, the massive, long duration
cyclone at the beginning of August-2012, and the list goes on and on.
AMEG being extreme? Hardly, more like science compartmentalization
and specialization being myopic to the collection of system changes
that are screaming out that the climate system has entered a period
of abrupt change that has not been seen before in human history, but
has happened many times in the paleorecords. In fact, rates of change
now are at least 10x higher than any seen in the geologic record.
SkepticalScience: About
a week ago, a Nature article by
Gail Whiteman, Chris Hope, and Peter Wadhams came out analyzing the
"Vast Costs of Arctic Change." The Whiteman article is an
honest and thoughtful commentary about the economic impacts of a
changing Arctic climate. I will not comment on their economic
modeling here, but rather on a key scenario assumption that they use
which calls for vast increases in Arctic-sourced methane to the
atmosphere. In this case, they have in mind a very rapid pulse of 50
Gigatons of methane emanating from the East Siberian Shelf
(see image,
including Laptev and East Siberian sea). Note: 1 GtCH4= 1 Gigaton of
methane = 1 billion tons of methane. Whiteman et al. essentially
assume that this "extra methane" will be put in the
atmosphere on timescales of years or a couple decades. This article
has been widely publicized because it calls for an average of 60
trillion dollars on top of all other climate change costs. Since this
was discussed in a prediction context rather than as a thought
experiment, it demands analysis of evidence.
In
this article, I will argue that there is no compelling evidence for
any looming methane spike. Other scientists have spoken out against
this scenario as well, and I will encompass some of their arguments
into this piece. In summary, the reason a huge feedback is unlikely
is because of the long timescale required for global warming to reach
some of the largest methane hydrate reservoirs (defined later) (Paul
Beckwith: no methane was expected from ESAS since seafloor was
thought to be impermeable, until it was measured to rapidly outgas
from one year to the next), and
because no evidence exists for such an extreme methane concentration
sensitivity to climate in the past record (Paul
Beckwith: methane pulses released over several years or a few decades
is not detectable in ice cores since bubble closure below firn takes
about 50 years or more).Permafrost
feedbacks are of concern, but there is no basis for assuming a
dramatic "tipping point" in the atmospheric methane
concentration (Paul
Beckwith: no basis for this statement since observations show large
increase in methane).
The
Methane Tour
Methane
(CH4) is a greenhouse gas. It absorbs thermal energy that the Earth
is trying to shed into outer space, and can thus warm the surface of
the planet. Its concentration in the modern atmosphere is a little
bit shy of 2 parts per million by volume (ppm), compared to roughly
0.72 ppm in 1750 or 0.38 ppm in typical glacial conditions. Like CO2,
methane has not risen to modern day concentrations during the
entirety of the now ~800,000 year long ice core record.
So
what about Whiteman's scenario?
For
perspective on how big 50 GtCH4 is, I've used data from David
Archer's online
methane model to
see how atmospheric methane concentrations would change in response
to such a big carbon injection. You can do this as a back-of-envelope
calculation by noting that 1 ppm is about 2.8 GtCH4 if it all stays
as methane and isn't removed, but this model lets you see the decay
timescale too. For methane, the decay back to original concentrations
occurs within decades, whereas for CO2 it takes millennia (CH4 is
rapidly oxidized by the hydroxyl radical in the atmosphere).
Therefore, CO2 dominates the long-term climate change picture but the
methane spike can induce very large transitory effects. (Paul
Beckwith: keep in mind that the methane lifetime varies greatly
depending on the availability of the hydroxyl radical. On average it
is 12 years, however in dry regions like the Arctic with little water
vapor it is longer, while at moist equatorial regions it is shorter).
I've
run two scenarios in which the 50 GtCH4 injection takes 1 year and 10
years to complete (red and blue lines, respectively). The model
starts with pre-industrial CH4 concentrations in years -10 through
zero. The modern concentration of methane is shown as a horizontal
orange line.
Everything
having to do methane in the ice core record resides below the orange
line in Figure 1 (at least within the resolution of the cores). So
we're potentially talking about a very big change, which the Whiteman
article contends is likely to be emitted fairly soon and should have
implications for Arctic policy. (Paul
Beckwith: This graph clearly demonstrates that if glacial ice bubble
closure takes 50 years, then the pulse will not be captured. Also,
the molecular weight of CH4 is 16 compared to 30 or so for air
(mostly N2) so the methane does not stay around the surface for
long).
For
many, the primary concern about “big” abrupt changes in
atmospheric CH4 stems from the large quantity of CH4 stored as
methane hydrate or in permafrost in the Arctic region. These terms
are defined below. It should be noted that globally, wetlands are the
largest single methane source to the modern atmosphere. Most of that
contribution is from the tropics and not from high latitudes (even if
the Arctic was to start pumping harder). The Denman
et al., 2007 carbon
cycle chapter in the last IPCC report is a useful reference. (Paul
Beckwith: methane from wetlands in tropics has short lifetime due to
extremely large quantities of water and thus hydroxyl ions in that
region, as opposed to methane from the Arctic in much drier
conditions)
Nonetheless,
the Arctic is a region that is quite dynamic and is changing rapidly.
The high latitudes are currently a CO2 sink (Paul
Beckwith: this cannot be correct, since CO2 concentrations are higher
in the Arctic than the global values measured at Mauna Loa, for
example) and
CH4 source in the modern atmosphere, and it’s not implausible that
the effectiveness of the sink could diminish (or reverse) or that the
methane source could enhance in the future, since we expect a
transition to a warmer, wetter climate with an extended thawing
season. This makes the carbon budget in the Arctic a “hot” place
for research.
In
these discussions, it is important to clarify what sort of methane
source we're talking about.
Methane
hydrate is a solid substance that forms at low temperatures / high
pressures in the presence of sufficient methane. It is an ice-like
substance of frozen carbon, occurring in deep permafrost soils,
marine continental margins, and also in deeper ocean bottom
sediments. It's also very concentrated (a cubic foot of methane
hydrate contains well over 100 times the same volume of methane gas).
On
the decade-to-century timescale, the liberation of methane from the
marine hydrate reservoir (or the deep hydrates on land) should be
well insulated from anthropogenic climate change. Deep ocean
responses by methane are a very slow response (many centuries to
millennia, Archer
et al., 2009).
Methane released in deep water also needs to evacuate the water
column and get to the atmosphere in order to have a climate impact,
although much of it should get eaten up by micro-organisms before it
gets the chance. These issues are discussed in a review paper
by O’Connor
et al., 2010. (Paul
Beckwith: Methane response in deep ocean is not always slow, thus
this section is very misleading. Underwater landslides from slope
instability or earthquakes are know to have resulting in large
methane pulses many times in the paleorecords. For example, Storegga
off Norway or off New Zealand, there are extensive pockmarks on the
ocean floor indicating abrupt episodic events. The mainstream view
that methane outgassing from deep water regions does not enter the
atmosphere. If release is slow that is correct, however rapid
outbursts overwhelm the micro-organisms and result in large amounts
of methane entering the atmosphere. Even slower releases from deep
water off Svalbard have been observed recently to enter the
atmosphere; another unexpected development).
There’s
also carbon in near-surface permafrost, which is the more vulnerable
carbon pool during this century. Permafrost is frozen soil (perennial
sub-0°C ground), and can also encompass the sub-sea permafrost on
the shelves of the Arctic Ocean. This includes the eastern Siberian
shelf, a very shallow shelf region (only ~10-20 m deep, and very
broad, extending a distance of 400– 800 km from the shoreline).
This is a bit of a special case. These subsea deposits formed during
glacial times, when sea levels were lower and the modern-day seafloor
was instead exposed to the cold atmosphere. The ground then became
submerged as sea levels rose (going into the warmer Holocene). The
rising seas have been warming the deposits for thousands of years.
Because of their exposure during the Last Glacial Maximum, the
shelves may be almost entirely underlain by permafrost from the
coastline all the way down to a water depth of tens or even a hundred
meters (e.g., Rachold
et al., 2007 and this USGS
page).
There's
actually no good evidence of shallow hydrate on the Siberian shelves,
even though there are substantial quantities of subsea permafrost.
Hydrate may exist deeper down however, more than 50 meters below the
seafloor. The stability of these hydrates is sustained by the
existence of permafrost, and it's not quite clear to what extent
hydrate can also be stored within the permafrost layer. (Paul
Beckwith: Permafrost people have an over-reliance on uniform slab
models which examine time taken for heat to propogate through the
slabs to melt the deep permafrost. They severely underestimate the
fracturing and nonuniform nature of the permafrost, presence of
taliks, etc. All that is needed is one weak spot or fracture region
and heat can transfer downward much faster and further than the
models suggest. Similar slab models are used to estimate glacial ice
melting and they have clearly been incorrect and completely
underestimate the rates of melting from dynamic effects and Moulin
pathways, for example.)
The
estimates of the amount of methane in these various Arctic reservoirs
are very uncertain. Ballpark numbers are a couple thousand gigatons
of carbon (GtC) stored in hydrates in global marine sediments
(e.g., Archer
et al., 2009)
of which a couple hundred gigatons of carbon are in the Arctic Ocean
basin, and between 1000-2000 GtC in permafrost soil carbon stocks
(e.g., Tarnocai
et al., 2009)
after you include the deeper deposits. For comparison, there is a bit
over 800 GtC in the atmosphere, of which about 5 Gt is in the form of
methane, and estimated ~5000 GtC in the remaining fossil fuel
reserve. These numbers seem big compared to the atmosphere, but for
methane direct comparison isn't too relevant unless you put it in
rapidly, since it has such a short lifetime in the atmosphere. Large
amounts of CO2, in contrast, last much longer.
A
couple years ago, Shakhova
et al. (2010a) reported
extensive methane venting in the eastern Siberian shelf and suggested
that the subsea permafrost could become unstable in a future warmer
Arctic. Shakhova
et al (2010b) cite
~1400 Gt in the East Siberian Arctic Shelf, which comprises ~25% of
the Arctic continental shelf and most of the subsea
permafrost. Shakhova
et al (2010c) ran
through a few different pathways in which they argued for 50 GtCH4
release to the atmosphere either in a 1-5 year belch or over a 50-yr
smooth emission growth, which they suggest, “significantly
increases the probability of a climate catastrophe.” This
assessment was the foundation for the concern in the recent Whiteman
Nature article, linked at the top.
The
physical mechanism outlined by some of these authors is related to
the rapid reduction in Arctic summer sea ice observed over the last
few decades, which allows for greater amounts of solar radiation to
penetrate the waters around the Arctic shelf. Warming water
propagates down in the well-mixed layers tens of meters to the
seabed, and might melt frozen sediments underneath. Because the shelf
in this region is shallow (compared to other regions), one doesn't
need to wait a long time for the seafloor to feel the
atmosphere-surface forcing, and methane leakage might have an easier
escape path to the atmosphere. Allegedly, this has been leading to an
acceleration of methane flux.
Responses
from Scientists
As
a response to the first paper from Shakhova on enhanced methane
fluxes, Petrenko
et al (2010)criticized
the authors for misunderstanding several of their references and
primarily for the logical implications of their conclusions. For
example,
“A
newly discovered CH4 source is not necessarily a changing source,
much less a source that is changing in response to Arctic warming.
Shakhova et al. do acknowledge these distinctions, but in these times
of enhanced scrutiny of climate change science, it is important to
communicate all evidence to the scientific community and the public
clearly and accurately”
(Paul
Beckwith: Examination of the methane concentrations in the atmosphere
in the Arctic region from AIRS satellite data over a decade or so
shows an obvious large increase in the amount of methane, and has
been corroborated with flask measurements at locations across the
Arctic, namely Barrow, Alaska and Svalbard. How is this not a
changing source?)
Another
paper, Dmitrenko
et al (2011) reinforced
this statement and came to the conclusion that there is currently no
evidence that Arctic shelf hydrate emissions have increased due to
global warming. This is also discussed in the review article by
O'Connor et al (2010, linked above). (Paul
Beckwith: Again, does one trust a direct observation or a conclusion
from a paper? Obviously the direct observation.)
The
work done by the Dmitrenko paper shows that although the changing
Arctic atmosphere has led to warmer temperatures throughout the water
column (over the eastern Siberian shelf coastal zone), it takes a
very long time for the permafrost feedback at the bed to respond to
this signal. They noted that the deepening of the permafrost table
should only have been on the order of 1 meter over the last several
decades, which does not permit a rapid destabilization of methane
hydrate. (Paul
Beckwith: Deepening of the permafrost table of 1 meter over several
decades is based on a slab model and let to the erroneous mainstream
view that the seafloor over the ESAS was impermeable to methane
release. Measurements show otherwise.)
It
is important to emphasize that simple point source emission estimates
are not often suitable for determining changed sources and sinks over
the last few decades, and thus don't tell you how that translates
into atmospheric concentration. This should be kept in mind when
seeing dramatic videos of methane venting from a shelf or exploding
lake,
which might not actually have much to do with global warming. (Paul
Beckwith: This is a very alarming view, and would fit in fine on any
of numerous climate denial websites. Rapid methane emissions in the
Arctic are what they are. Call a spade a spade.)
In
2008, there was a comprehensive report on Abrupt Climate Change from
the U.S. Climate Change Science Program, which is a bit dated but
nonetheless makes a statement reflecting most of current scientific
thinking. Quoting Ch.
5 Brook et al (2008):
"Destabilization
of hydrates in permafrost by global warming is unlikely over the next
few centuries (Harvey and Huang, 1995). No mechanisms have been
proposed for the abrupt release of significant quantities of methane
from terrestrial hydrates (Archer, 2007). Slow and perhaps sustained
release from permafrost regions may occur over decades to centuries
from mining extraction of methane from terrestrial hydrates in the
Arctic (Boswell, 2007), over decades to centuries from continued
erosion of coastal permafrost in Eurasia (Shakova [sic] et al.,
2005), and over centuries to millennia from the propagation of any
warming 100 to 1,000 meters down into permafrost hydrates (Harvey and
Huang, 1995)" (Paul
Beckwith: Again, slab model thinking. Episodic events like landslides
negate these claims, as does fractures and other weakspots in the
slabs which allow pathways for huge heatflow. A good analogy is
polyanas in sea ice that allow for enormous heat flow between the
ocean and the atmosphere in a sea ice field.)
Paleo-Analogs
One
of the primary reasons we don't think there's as much methane
sensitivity to warming as has been proposed by Shakhova, and argued
for in the Whiteman Nature article, is because there's no evidence
for it in the paleoclimate record. This has been a point made
by Gavin
Schmidt on
Twitter (a compilation of his many tweets on the topic here)
but the objections to the Nature assumptions have been further echoed
in recent days by other scientists working on the Arctic methane
issue (e.g., here,here).
One
can argue from a process-based and observations-based approach that
we don't understand everything about Arctic methane feedback
dynamics, which is fair. Nonetheless, the methane changes on the
scale being argued by Whiteman et al. should have been seen in the
early Holocene (when Summer Northern Hemispheric solar radiation was
about 40 W/m2 higher than today at 60 degrees North, 7000-9000 years
ago). (Paul
Beckwith: Earth tilt was larger, so Winter Northern Hemispheric solar
radiation was about 40 W/m2 lower than today at 60 degrees North.
Thus, the ice formed much more quickly and much thicker in the winter
back then. Also, at night much more heat was radiated out to space in
the lower GHG world then as compared to our 400 ppm levels
today). Even
larger anomalies occurred during the Last Interglacial period between
130,000 to 120,000 years ago, though with complicated regional
evolution (Bakker
et al., 2013).
Both
of these times were marked by warmer Arctic regions in summer without
a methane spike. It's also known pretty well (see here)
that summertime Arctic sea ice was probably reduced in extent or
seasonally free compared to the modern during the early Holocene,
offering a suitable test case for the hypothesis of rapid, looming
methane release. (Paul
Beckwith: Incorrect, the summertime Arctic is not believed to be
seasonally ice free during these periods. The last time this happened
was likely 2 or 3 million years ago.)
It
should be noted that Peter Wadhams did offer a response recently
to the criticisms of the Whitehead Nature piece (Wadham is a
co-author) but did not address why this idea has not been borne out
paleoclimatically.
Yesterday,
an objection to the paleoclimate comparison cropped
up in
the Guardian suggesting that the early Holocene or Last Interglacial
analogs are not suitable pieces of evidence against rapid methane
release. They aren't perfect analogs, but the argument does not seem
compelling. (Paul
Beckwith: Colder winters in the early Holocene and Last Interglacial
and much colder nights (in summers and winters then) meant much
thicker and extensive ice formation in winters, and slower melting at
night, respectively. Compelling arguments.) The
Northeast Siberian shelf regions have been exposed many times to the
atmosphere during the Pleistocene when
sea levels were lower (and not covered by an ice sheet since at least
the Late Saalian, before 130,000 years ago, e.g.,
here).
As mentioned before, when areas such as the Laptev shelf and adjacent
lowlands were exposed, ice-rich permafrost sediments were deposited.
The deposits become degraded after they are submerged (when sea
levels increase again), resulting in local flooding and seabed
temperature changes an order of magnitude greater than what is
currently happening. Moreover, the permafrost responses have a lag
time and are still responding to early Holocene forcing (some
overviews in e.g., Romanovskii
and Hubberten, 2001; Romanovskii
et al., 2004; Nicolsky
et al., 2012).
A book
chapter by
Overduin et al., 2007 overviews the history of this region since the
Last Glacial Maximum. These texts also suggest that large amounts of
submarine permafrost may have existed going back at least 400,000
years. It therefore does not seem likely that the seafloor deposits
will be exposed to anything in the coming decades that they haven't
seen before. (Paul
Beckwith: What is unique now is the extremely high concentration
levels of CO2 (400ppm) and CH4 (>1900ppb). These high
concentrations trap the heat in the troposphere 24/7. Thus, at night
heat loss is limited by the GHG blanket. At all previous times the
GHG blanket was much weaker, with CO2 ranging from 180 to 280 ppm and
CH4 ranging from 350 to 700 ppb, or so. This makes an enormous
difference.)
What
about other times in the past? Fairly fast methane changes did occur
during the abrupt climate change events embedded within the last
deglaciation (e.g., Younger Dryas), just before the Holocene when the
climate was still fluctuating around a state colder than today. These
CH4 changes were slower than the abrupt climate changes themselves,
and have been largely attributed to tropical and boreal wetland
responses rather than high latitude hydrate anomalies. Marine hydrate
destabilization as a major driver of glacial-interglacial CH4
variations has also been ruled out through the inter-hemispheric
gradient in methane and hydrogen isotopes (e.g., Sowers,
2006) (Paul
Beckwith: Episodic events like landslides, as mentioned before,
cannot be discounted. In fact geological events like landslides occur
at much higher frequencies when there is a rapid temperature
transition, as covered extensively in Bill McGuire’s new textbook.
Also, the text on “The Clathrate Gun hypothesis” cannot be
completely discounted.)
To
be fair, we don't have good atmospheric methane estimates during
warmer climates that prevailed beyond the ice core record, going back
tens of millions of years. Methane is brought up a lot in the context
of the Paleocene-Eocene Thermal Maximum (PETM, 55 million years ago).
During this time, proxy records show global warming at the PETM
(similar to what modern models would give for a quadrupling of CO2),
extending to the deep ocean and lasting for thousands of years. In
addition, there were substantial amounts of carbon released. It may
very well be that isotopically light carbon came from a release of
some 3,000 GtC of land-based organic carbon, rather than a
destabilization of methane hydrates, although this is a topic of
debate and ongoing research (see e.g., Zeebe
et al., 2009;Dickens
et al., 2011).
It's
also important to emphasize that any destabilization of oceanic
methane hydrates at the PETM, or any other time period, would imply
that the carbon release is a feedback to some ocean warming that
occurred first- perhaps on the order of 1000 years beforehand.
Furthermore, once methane was in the atmosphere, it would oxidize to
CO2 on timescales significantly shorter than the PETM itself
(decades.) Unfortunately, there is no bullet-proof answer right now
for what caused the PETM, but rather several hypotheses that are
consistent with proxy interpretation. However, methane cannot be the
only story.
The
Role of Methane in Climate (Change)
To
be clear, CH4 is important as we go forward, and is already a key
climate forcing agent behind CO2 (coming in at ~0.5 W/m2 radiative
forcing since
pre-industrial times). Additionally, methane is quite reactive in the
atmosphere, and the effect of other things like tropospheric ozone,
aerosols, or stratospheric water vapor are partly slaved to whatever
is happening to methane (Shindell
et al., 2009).
This means methane emitted has a bigger collective impact on climate
than if you just do the radiative forcing calculation by comparing
methane concentration changes to what it was in 1750. (Paul
Beckwith: It is important to point out an enormous misconception in
public and scientific reports on methane regarding the Global Warming
Potential (GWP). A number in the low 20s is almost always reported
(22x, 25x…) and is based on a 100 year timescale. On a 20 year
timescale, methane GWP is around 70x, and on a 1 or 2 year timescale
the GWP is >150x. Clearly, in terms of methane in the Arctic
sourced from marine or terrestrial permafrost the number of
significance to sea ice and localized warming is 150x.)
Permafrost
thawing is also going to be important in the coming century (this is
a good paper), and the uncertainties pretty much go one way on this.
There's not much wiggle room to argue that permafrost will reduce
CH4/CO2 concentrations in the future. This is also likely to be a
sustained release rather than one big catastrophic event. For
example, permafrost was not included in Lenton
(2008) as
a "tipping point" for precisely the reason that there's no
evidence for any "switch" of rapid behavior change. (Paul
Beckwith: Exclusion of methane as a “tipping element” in this
paper by the “experts” in 2008 was based on rates of change based
on slab models, which recent observations of emissions has clearly
invalidated). Much
of the carbon is also likely to be in the form of CO2 to the
atmosphere, and even implausible thought experiments of catastrophic
methane release (see David Archer's post at
RealClimate) give you comparable results in the short-term as to what
CO2 is going to do for a long time.
Conclusion
The
observed methane venting from the East Siberian shelf sea-floor to
the atmosphere is probably not a new component of the Arctic methane
budget. Furthermore, warming of the Arctic waters and sea ice decline
will likely impact subsea permafrost on longer timescales, rather
than the short term. (Paul
Beckwith: Is this author so sure of this as to be willing to stake
the stability/instability of the entire global circulation system on
this?)
Methane
feedbacks in the Arctic are going to be important for future climate
change, just like the direct emissions from humans. This includes
substantial regions of shallow permafrost in the Arctic, which is
already going appreciable change. Much larger changes involving
hydrate may be important longer-term. Nonetheless, these feedbacks
need to be kept in context and should be thought of as one of the
many other carbon cycle feedbacks, and dynamic responses, that
supplement the increasing anthropogenic CO2 burden to the atmosphere.
There is no evidence that methane will run out of control and
initiate any sudden, catastrophic effects. (Paul
Beckwith: There is no evidence that methane will not run out of
control, in light of large increases of concentrations in recent
years). There's
certainly no runaway greenhouse. Instead, chronic methane releases
will supplement the primary role of CO2. Eventually some of this
methane oxidizes into CO2, so if the injection is large enough, it
can add extra CO2 forcing onto the very long term evolution of global
climate, over hundreds to thousands of years.
Errata
Update SkepticalScience: Gavin Schmidt let me know that in the first
version of this post, I used gigatons of carbon instead of gigatons
of methane. I mistakingly read the Shakhova paper as an injection of
carbon. Since the molecular weight of carbon is 12 g/mol, and CH4 is
16 g/mol, then 1 GtC=1.33 GtCH4. The figure in the post has been
revised accordingly and doesn't impact the argument here.
Related
-
Arctic Methane Release: "Economic Time Bomb"
-
Methane Hydrates
-
Arctic Methane FAQ