Why the jury's still out on the risk of Arctic methane catastrophe
About a week ago, climate scientist
Michael Tobis wrote a critique of
my 'Seven facts about the Arctic
methane time bomb ' following a
twitter exchange with him and
Chris Colose, author of an article at
Skeptical Science arguing that the
core scenario of a new Nature
paper by Gail Whiteman et. al on
the economic costs of Arctic climate
change is extremely unlikely.
Much of this debate kicked off
because the said Nature paper
advances a hypothetical scenario
for an abrupt Arctic methane
release over either a decade or
several decades of about 50
gigatonnes (Gt), and argues
specifically that such a scenario is
"likely." My own attempt to
understand the literature
convinced me that the scenario
should be viewed as a serious
possibility.
Tobis on the other hand is the latest
amongst several scientists offering
scathing criticisms of that scenario,
which in his own words is "as close
to impossible as anything in earth
science; actual geophysics refutes
it."
He begins with my first point, 1.
The 50 Gigatonne decadal
methane pulse scenario was
posited by four Arctic specialists,
and is considered plausible by
Met Office scientists.
Tobis writes that the Review of
Geophysics paper I cite says
"Arctic thawing may release in
excess of 50 GT of C [Carbon], a
very serious matter... But Ahmed
refers to the paper in support of a
very different assertion, that 50 GT
of methane would be released...
But the paper to which he points
says nothing of the sort. I conclude
that he doesn't really know what he
is talking about. Specifically he has
already shown that he is confused
about the distinction between
methane releases and CO2
releases."
However, the carbon release
scenarios from permafrost
explored by the paper include both
methane and carbon. Here's what
the paper says:
"The most important determinant
of whether release of frozen
carbon happens as CO2 or CH4
[methane] is whether
decomposition proceeds
aerobically or anaerobically... In
anaerobic conditions, a greater
proportion of soil organic carbon
decomposition is released as CH4,
although not all of it necessarily
reaches the atmosphere."
Following this paragraph, the paper
cites several scenarios for large-
scale releases from permafrost
carbon, including the 50-100 Gt
carbon release I mentioned.
Further down, the paper continues:
"Thawing of the terrestrial
permafrost will result in CO2 and
CH4 emissions on time scales of a
few decades to several centuries."
So Tobis is wrong in assuming that
the carbon release scenarios the
paper is discussing are only CO2 -
that isn't specified, so I'd assumed
the paper was open on whether the
50-100 Gt emissions were methane
or carbon.
This was a mistake, however. The
paper makes clear that although the
scenarios are not clear on the
precise quantification of carbon
dioxide compared to methane
releases from permafrost thawing,
methane releases would be only be
a small percentage of the overall
carbon release scenarios explored.
So Tobis is ultimately correct - the
paper does not back up the specific
scenario endorsed as likely by the
Nature paper. I stand corrected
on that.
Therefore, the plausibility of the
specific 50 Gt scenario rises and
falls on the credibility of the four
Arctic specialists, including Dr.
Natalie Shakhova, who came up
with the scenario in the first place.
That leaves point 1 only half intact,
so we're left with:
1. The 50 Gigatonne decadal
methane pulse scenario was
posited by four Arctic specialists
Tobis unfortunately addresses this
with only an ad hominem attack
on the expertise of these Arctic
specialists:
"Whether we should be
acknowledging the 'Arctic
specialists' as actually expert is,
frankly, the question at hand."
Tobis goes through my other
citations of the literature arguing
that I am confusing quantities and
making unwarranted
extrapolations. However, my
citations of this literature is simply
to clarify that the literature does
not rule out potentially dangerous
releases of Arctic methane. Does
Tobis manage to refute point 2.
Arctic methane hydrates are
becoming increasingly unstable
in the context of anthropogenic
climate change and it's impact on
diminishing sea ice ? No. Arctic
methane hydrates are becoming
increasingly unstable. I said
nothing more, or less, than exactly
that.
What about fact 3. Multiple
scientific reviews, including one
by over 20 Arctic specialists,
confirm decadal catastrophic
Arctic methane release is
plausible?
Tobis concedes "A couple of
reviews do give some support to
this, but are vague about time
scales". He then links to what he
describes as a "DOE report".
Instead, the link goes through to a
Geophysical Research Letters study,
which, however, he completely
ignores, instead quoting from the
original Review of Geophysics
paper as follows: "The risk of a
rapid increase in [methane]
emissions is real but remains
largely unquantified..."
And he calls me confused!
He then argues that there is "plenty
of room for acceleration without
hitting the cataclysmic level.
Further evidence doesn't support
the immediacy of that scenario at
all."
But the Review of Geophysics paper
does NOT say that there is "plenty
of room for acceleration without
hitting the cataclysmic level" - it
says that:
"... significant increases in
methane emissions are likely, and
catastrophic emissions cannot be
ruled out."
The paper does NOT say available
evidence "doesn't support the
immediacy" of a catastrophic
scenario, but rather that
"uncertainties are large, and it is
difficult to be conclusive about the
time scales and magnitudes of
methane feedbacks."
As for the Geophysical Research
Letters study Tobis links to but
ignores, it says:
"... 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."
I think my fundamental contention
- that the scientific literature
recognises the possibility of some
sort of catastrophic methane
scenario - remains valid. Tobis is
right, however, to emphasise that
there is very little evidence
available on quantifying that
possibility.
In response to fact 4. Current
methane levels are
unprecedented , Tobis says yes, but
they are "not climbing rapidly",
and therefore this is mere "hype."
My intention here was not to
suggest that current Arctic methane
levels are definitive evidence of a
catastrophe already underway, but
simply to note that it is wrong to
say methane levels are NOT rising.
They are , and once again, Arctic
specialists are concerned.
According to Charles Miller of
NASA's new research programme,
Carbon in Arctic Reservoirs
Vulnerability Experiment (CARVE) :
"The CARVE science team is busy
analyzing data from its first full
year of science flights. What
they're finding, Miller said, is both
amazing and potentially troubling.
'Some of the methane and carbon
dioxide concentrations we've
measured have been large, and
we're seeing very different patterns
from what models suggest," Miller
said. "We saw large, regional-scale
episodic bursts of higher-than-
normal carbon dioxide and
methane in interior Alaska and
across the North Slope during the
spring thaw, and they lasted until
after the fall refreeze. To cite
another example, in July 2012 we
saw methane levels over swamps in
the Innoko Wilderness that were
650 parts per billion higher than
normal background levels. That's
similar to what you might find in a
large city.'
"Ultimately, the scientists hope their
observations will indicate whether
an irreversible permafrost tipping
point may be near at hand. While
scientists don't yet believe the
Arctic has reached that tipping
point, no one knows for sure. 'We
hope CARVE may be able to find
that "smoking gun," if one exists,'
Miller said."
So while NASA Arctic specialists say
Arctic methane levels are
"amazing" and "potentially
troubling", outside the range of
most model predictions, and
possibly indicative that "an
irreversible permafrost tipping
point" is near - a matter which "no
one knows for sure" - Tobis wants
to interpret all the evidence as
"refuting" any need for concern.
The other problem is that Arctic
monitoring is still poor, and might
be missing significant methane
emissions. As Shakhova and her co-
author Igor Semiletov told the New
York Times' Andy Revkin:
"It is no surprise to us that others
monitoring global methane have
not found a signal from the
Siberian Arctic or increase in
global emissions... The number of
stations monitoring atmospheric
methane concentrations worldwide
is very few. In the Arctic there are
only three such stations - Barrow,
Alert, Zeppelin - and all are far
away from the Siberian Arctic. We
are doing our multi-year
observations, including year-round
monitoring, in proximity to the
source. In addition to measuring
the amount of methane emitted
from the area, we are trying to
find out whether there is anything
specific about those emissions that
could distinguish them from other
sources. It is incorrect to say that
anyone is able to trace that signal
yet."
Most Arctic specialists recognise
that there's simply not enough
research to justify dismissing the
possibility of a catastrophe. That
sword cuts both ways, of course -
equally, there's not enough
research justifying conclusions that
we are definitely on the brink of a
catastrophe.
On 5. The tipping point for
continuous Siberian permafrost
thaw could be as low as 1.5C ,
Tobis concedes this "is on the
table", but that "it has nothing to do
with undersea methane." Um, I
never said it had anything to do
with undersea methane.
On 6. Arctic conditions during
the Eemian interglacial lasting
from 130,000 to 115,000 years
ago are a terrible analogy for
today's Arctic, he writes: "as a
response to Chris Colose" this is a
"terrible" response, "because Colose
is not relying on the Eemian but on
the early Holocene as the
analogous period." Yes, Colose does
refer to the early Holocene, but he
also repeatedly refers to the
Eemian, the "Last Interglacial
period between 130,000 to 120,000
years ago." In a previous article,
I'd already mentioned that in the
early Holocene, the East Siberia
Arctic Shelf (ESAS) was "not an
underwater shelf but a frozen
landmass" as reason to be sceptical
that paleoclimate data provides a
ready analogue for the present.
Tobis then launches an ad
hominem attack on climate
scientist Paul Beckwith, whom I
quoted for this article, and whom
Tobis refers to as:
"'Prof' Paul Beckwith, the
'Professor Beckwith' who is a grad
student at Ottawa U."
For the record, earlier this year,
Beckwith formally passed his PhD
examination on abrupt Arctic
climate change at the Laboratory
for Paleoclimatology and
Climatology, University of Ottawa,
where he is currently a part-time
professor in climatology. Rather
than addressing Prof Beckwith's
argument, Tobis wants to demean
his reputation and ignore his
argument (which he fails to refute).
Beckwith's full response to Colose
is here . Among Beckwith's points,
he argues that neither the early
Holocene nor Eemian offer good
analogues for the present Arctic:
"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... 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... 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."
If I was to take Tobis' approach, I
could have noted that Chris Colose
is a "grad student" at the University
of Albany. I didn't, because it's
irrelevant.
Finally, Tobis takes on fact
7.Paleoclimate records will not
necessarily capture a large,
abrupt methane pulse with the
following obfuscation: "Now, we
swing back to saying that it HAS
occurred in the recent geological
past, indeed at the time which
Colose says is the better analogy."
This is incorrect. Here, I merely
point to a paper in Science by
Nisbet which argues specifically
that the cold Younger Dryas was
ended due to methane emissions
which came mostly from wetlands,
but for which the initial trigger
could have been Arctic methane
clathrates:
"A possible explanation for the
sudden end of the Younger Dryas is
that, at a time of high Arctic
insolation, an initial outburst of
methane - perhaps from a
geological source such as methane
clathrates - triggered global
warming, initiating both strong
wetland emission in the tropics and
north (8), and further hydrate
responses as the thermal shock
penetrated the permafrost (9, 10),
freeing methane from decomposing
clathrate hydrates and releasing
gas pools trapped beneath them."
The evidence for this, however, is
inconclusive, so the paper
concludes: "The jury thus remains
out on the initial trigger..."
On the issue of whether
paleoclimate records will actually
capture a large, abrupt methane
pulse such as the scenario proposed
by Shakhova et. al, as this paper in
Earth and Planetary Science Letters
observes, "rapid methane
perturbations in the atmosphere
are strongly smoothed in ice core
records" due to "the relatively short
atmospheric lifetime of methane."
So it is quite possible that an
abrupt, catastrophic methane
release of the sort Shakhova
proposes has happened, but is
undetected in ice cores.
Tobis then declares a "scientific
consensus has been reached" that
Shakhova's scenario is "implausible
in the extreme."
But the scientific consensus
amongst ESAS experts is quite
different, as I'd already noted. A
peer-reviewed study by 20 Arctic
specialists of ESAS data from
1995-2011, drawing of course also
on Shakhova's work, specifically
recognises:
"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."
It seems clear to me that the
scientific literature on the danger
of an Arctic methane catastrophe
recognises the possibility
unequivocally, but highlights huge
uncertainty in our knowledge of
the processes at work. Most of the
literature I've been able to find on
this subject shows great humility -
and while acknowledging the
possibility of worst-case scenarios,
makes quite clear that the
likelihood of those scenarios is
very difficult to gauge.
The Nature paper by Whiteman et.
al went too far in stating the
Shakhova et. al scenario as
"likely". But on the other end of
the spectrum, in the comments to
his own blog, Tobis hints that
Shakhova et. al are involved in
"junk science" - despite the fact that
their papers have been published in
peer-reviewed journals (their 50 Gt
scenario is discussed in this paper
originally published in the
Proceedings of the Russian
Academy of Sciences), and that
their general thesis is taken
seriously by the US National
Science Foundation.
