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Toward Improved Discussions of Methane & Climate

Posted on 1 August 2013 by Chris Colose

Update- See Correction of an error at bottom

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.

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), and because no evidence exists for such an extreme methane concentration sensitivity to climate in the past record.  Permafrost feedbacks are of concern, but there is no basis for assuming a dramatic "tipping point" in the atmospheric methane concentration.

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. 

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.

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. 

Nonetheless, the Arctic is a region that is quite dynamic and is changing rapidly.  The high latitudes are currently a CO2 sink 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.

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.

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”

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).

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.

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.

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)"


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).  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.

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. 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., 2004Nicolsky 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.

 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)

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. 

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.  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. 


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.

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.  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: 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.

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Comments 1 to 50 out of 68:

  1. Chris Colose:

    A counter-argument to your position is presented in the article:

    Arctic methane catastrophe scenario is based on new empirical observations by Nafez Ahmed, Earth Insight, The Guardian, July 31, 2013

    Is there a middle-ground between your perspective and that of Ahmed's?   


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  2. Thanks for this excellent article. There appears to be a great deal of wishful thinking and handwaving among many of the proponents of this apocolypse scenario and its based around precious little information. 

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  3. One of the lines of evidence people point too is the increase in global methane levels since the mid 2000s. However this also co-incides with the huge surge in shale oil and gas drilling in the US. There has been a large amount of flaring of gas in these wells, espeically the Bakken, so it is more than a touch imprudent to conclude this new methane must be from the ESAS. 

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  4. #1- John

    I dedicated a paragraph to Ahmed's article in the Paleo-analog section

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  5. Chris Colose:

    Thank you. I had mistakenly assumed that you had finalized your OP before Ahmed's article was posted on The Guardian. 

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  6. The methane story that we should all be concerned about is this one given the way gas is being promoted and implemented as a "clean" alternative to coal.

    "As a longtime oil and gas engineer who helped develop shale fracking techniques for the Energy Department, I can assure you that this gas is not “clean.” Because of leaks of methane, the main component of natural gas, the gas extracted from shale deposits is not a “bridge” to a renewable energy future — it’s a gangplank to more warming ..."

    I recall reading in a Slate article about 6 months ago that Ray Pierrehumbert was working on a paper that looked at this issue - is anyone aware if that was published.

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  7. Further to @6, Ray Pierrehumbert has commented on natural gas and leakage here.

    I do not want to take the discussion on Chris's excellent article off topic. Perhaps SKS can look at this issue in the future.

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  8. mikeh,

    This is not the first time issue of gas leakage has been raised. I remember Ray Pierrehumbert's response in those previous occasions was the same: even if the leakage is higher than current estimates of 1%, then the short and long term climate effects are still far lower than the effects of burning coal for the equivalent amount of energy received.

    I completely agree with Ray here. The issue can be put to bed. Maybe one can show the actual minimal amount of extra forcings from increased methane concentrations due to leaks to prove the veracity of Ray's opinion. But I don't need that: the numbers in my head look obvious.

    The extraordinary claim of Whiteman et al article is a different matter because the amount of C release is much larger. The key circumstance they rely their claim on is the extraordinary condition of ESAS. For example, to the assertion of Gavin Schmidt, that Arctic used to be warmer in early Holocene and Eemian, they reply, quote:

    In the Early Holocene, the ESAS was not an underwater shelf but a frozen landmass, illustrating the pointlessness of this past analogy with contemporary conditions.

    This looks like the basic assumption why the permafrost & clathrate feedback "will be vastly different this time". I don't know what to think of this assumption because I'm not an expert. Maybe others will analyse it.


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  9. What I have failed to see in these discussions that could add a lot of insight are the following:

    1- A phase diagram for methane hydrates ( methane partial pressure -- fugacity, temperature, water chemical activity, CH4/H20 ratios in the hydrate). This is well known information from the oil/gas industry -- plugging pipelines and equipment with methane hydrates is a real problem for this industry that they solved in the 30's with a full understanding of both the thermodynamics and kinetics.

    2- Heat transfer calculations using well know math, at least for petrochemical engineers. It would be easy to calculate how fast it could melt the permafrost how deep.

    3- Very little discussion of the amount of methane in shallow permafrost and distinctions between recent biogenerated gases in thawed organic materials being anaerobically decomposed and historical gas in the permafrost.

    4- No real discussion of the microbiological response of the aquatic system. If methane seeps out of sediments in 50 meter deep water, it is reasonably soluble in the water phase and one would expect bacteria to oxidize it to CO2 and water using O2, NO2, NO3, S, etc. as the electron acceptor. Are there reports of huge hypoxic zones? If we are getting massive emissions from a large area, that massive area would be anaerobic and a dead zone before any methane gets into the atmosphere. People may be thinking of a little pot hole where methane can bubble up through a meter of water without being fully adsorbed into the water column, but deeper columns of water provide more (a calculable) ability to dissolve into the water column (a standard mass transfer problem). This is what happened to the huge amount of methane produced by the BP blowout in the Gulf and other methane seeps around the world.

    5- No discussion of the minimum substrate concentration (Smin) of methane oxidizing bacteria (the minimum concentration of methane) to support the growth of methane oxidizing bacteria in soils or in water. If you are above that Smin, bacteria can grow exponentially and reduce that concentration to Smin. We are hypothesizing a factor of 10 increase in the atmospheric concentration and that may cross the Smin level and soil bacteria will increase and dramatically speed up the removal kinetics.

    Considering the above, it appears that this Nature article was really “advocacy science” and not a real study of the issue. It is this type of “advocacy science” that is destroying the credibility of solid science in the publics mind. This type of advocacy has been common in “environmental science” for decades and effectively use against powerless opponents, like aquaculture in the US, but in this case opponents are not powerless and the amount of money at stake is significant on a world scale. The loss of credibility for science will be significant and very detrimental.

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  10. Good points, deweaver. Also not mentioned was the topography of the subsea ocean bed. There are many deep canyons, the walls of which could have methane stores that are quite close to the 'surface' that may degas violently at any moment, thereby destabilizeing the entire area, leading to more degassing.

    Also missing was any mention of the vast pools of highly presssurized free methane that lay beneath the permafost and hydrates, just needing a pathway to erupt explosively into the water above and thence into the atmosphere.


    Finally, how about the fact that well trained scientists with years of experience, such as Shakhova and Semiletov, have seen with their own eyes unprecedented levels of methane bursting into the atmosphere, burtst more than a k across.


    post script:


    Methane Hydrates - Extended Interview Extracts With Natalia Shakhova

    This is the last thing Shakhova says in the video:

    "strictly speaking, we do not like what we see there. Absolutely do not like."


    (pps. If dor can quote evidence that anyone is "wishful" for this calamity to happen, (s)he should link to evidence or stfu.)


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  11. Excuse the ignorance, but its often stated that methane has a comparatively short residency in the atmosphere, and so I've always assumed that the majority oxidises to CO2. Is this correct ? If not, what is the stable form of carbon that methane decomposes to.

    On the contrary, if so, is the extra CO2 generated by the any methane "plume" (of whatever size/duration) generally taken into account when modelling such scenarios ?

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  12. Phil @11, the methane (CH4) does oxidize to form a CO2 molecule and and two H2O molecules, the later condensing out of the atmosphere.  The CO2 has a significantly less powerful greenhouse effect per molecule than does CH4.  Therefore the result of the oxidation is to greatly decrease the greenhouse impact of the methane release.  And, yes, this is taken into account in modeling of the effecs of a methane release on climate.

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  13. deweaver @9, the Nature article explicitly cites independent literature to justify the claim of the potentialy large methane release.  It takes that claim from elsewhere and examines the potential economic impacts of such a release.  Given that, the lack of the technical discussion you are looking for is irrelevant.  Science builds on science.  If some other scientist has established a point to your satisfaction, it is not necessary to reestablish that point in any paper you publish seeking to use those results.  Consequently your claim that this is "advocacy science" is unwarranted, and reads like a simple slur intended encourage dismissal without thought.

    Please note that I say this despite being convinced by the evidence Chris Colose adduces that such a release is very unlikely, and also evidence from a David Archer article on Real Climate.  Science does not work be expecting all scientists to be convinced by what convinces you. 

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  14. Phil,

    Yes, CO2 is a product of methane oxidation (along with water vapor, which ends up having a non-negligible climate forcing in the stratosphere). 

    For fairly small perturbations, the "extra CO2" after oxidation isn't really important because there's so little of it.  There's a lot more CO2 in the atmosphere than methane.  So even if you turn methane into an extra ppm of CO2, that's not even a years worth of fossil fuel burning.  For much larger methane releases, however (hundreds to thousands of gigatons), that can add on significantly to the long term radiative forcing, even after oxidizing to CO2.  They key here is the different lifetimes of the two gases, which isn't adequately captured in existing metrics to compare different gases (like GWP).  

    The fate of a big methane injection after it oxidizes comes up in some deep-time discussions, like Snowball Earth.  By the way, for slow releases, you'd sustain higher steady-state methane concentrations during the timeframe that the release is occurring. So a slow release is still an issue.   But it's unclear to me that methane has ever been a "huge" player in climate change on Earth, at least since the planet was filled with lots of oxygen in its atmosphere (I use the word "huge" in a bigger-picture context than the still significant radiative forcings that we're talking about for contemporary global warming, e.g., for the evolution of climate over the last 60 million years, or the deglaciation of a Snowball Earth). For understanding the evolution of global climate, CO2 is much more first order.


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  15. The issue I have with this article is that it paints scientists who have found evidence of a potential rapid methane release as a near equivalent to climate change deniers.

    In addition, the article clearly sides with scientists who have a very conservative view on the issue of methane release. So conservative, in fact, that all science indicating a potential for anything other than a very slow release is painted in a light so as to be considered false.

    Though PETM ocean floor heating, slope collapse and methane hydrate release theory as a mechanism for final rapid atmospheric heat increase and coordinate anoxic ocean state are just that, numerous scientific papers support evidence for such events. Wadhams and Shakova are just a few of the scientists who have issued concerns for such events in a contemporary ocean and land system due to human caused warming. Hansen, for example, has mentioned risk of methane release, both from hydrates and from land material, as a reason for keeping human CO2 levels low. So I must ask the question? Is Hansen being irresponsible?

    Further, this particular post seems to fail to take into account contemporary research showing high risk of a substantial contribution from Arctic carbon stores in the form of both methane and CO2 on the order of 43 to 135 gigatons CO2e by 2100. The study, conducted by a number of scientists for the UN is available here:

    Were these scientists being irresponsible by indicating methane as a potent amplifying feedback from now to 2100 and even moreso through 2200?

    Now this particular study does not specifically indicate a potential yearly release on the order of 1-50 gigatons methane, as Shakova warns is possible. But it does indicate methane as an amplifying feedback of significant magnitude on a time scale that includes a more rapid response than that seen in the Eemian or during the most recent interglacial. It also, contrary to what Archer has stated in earlier articles, shows that emissions lower than this level are significant.

    I suppose what I find most concerning is the fact that Skeptical Science seems to have hitched itself to the, albeit professional, opinion of a few scientists who are very conservative on the issue of methane release without attempting to identify probabilities for a catastrophic release or exploring a middle ground, available in a number of reports, in which release is an important addition to CO2 forcing. The science, on this issue, includes all the scientists -- Shakova, Wadhams, Hansen, White, and others showing evidence of potential catastrophic release, others whose models indicate a more modest release, and Schmidt, Archer and others who seemingly believe that methane is almost a non-issue when it comes to climate change.

    To quote NASA scientist and CARVE researcher Charles Miller:

    "Permafrost soils are warming even faster than Arctic air temperatures - as much as 2.7 to 4.5 degrees Fahrenheit (1.5 to 2.5 degrees Celsius) in just the past 30 years," Miller said. "As heat from Earth's surface penetrates into permafrost, it threatens to mobilize these organic carbon reservoirs and release them into the atmosphere as carbon dioxide and methane, upsetting the Arctic's carbon balance and greatly exacerbating global warming."

    Is Charles Miller the alarmist equivalent of a climate change denier or are his points worth considering? I'd, therefore, compell Skeptical Science to widen its scope in coverage on the issue of methane. The breadth of science indicates instances of Arctic emissions happening now, not at catastrophic levels, but at levels indicative of concern. A valid theory supported by top scientists shows potentials for catastrophic releases of hydrates during major ocean warming events. More moderate research indicates a likelihood of significant but not catastrophic releases from now to 2100. Since neither Archer nor Schmidt can provide compelling evidence as to why their theory of 'slow release' should dominate, since they rely on a static rather than dynamic view of Arctic systems (Eemian and Holocene corrollaries), and since they seem to exclude other Earth Systems Sensitivity factors, it would seem that their views require much stronger evidence to be reassuring and that we should still consider Wadhams, Hansen and Shakhova as providing a valid warning worthy of policy consideration.

    Finally, if Schmidt and Archer are correct, then we lose nothing except a little extra effort and gaining more certainty and resiliency by acting. But if Wadhams, Shakhova and Hansen are correct, then in failing to act and gain greater understanding of potential risks, we lose a great deal.


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  16. Yes, but Chris, methane catastrophes have arguably happened before, during the End Permian, the End Triassic, a couple of events in the Jurassic, and the End Paleocene (aka the PETM). Certainly, there have been a series of mass extinctions, with similar signatures in the carbon isotope ratios- a massive carbon isotope excursion best explained by the entry of several trillion tons of C12 enriched hydrate methane into the atmosphere. Or, one could postulate much, much larger amounts of CO2- except that the math does not quite work out.

    So, it's not just a theoretical possibility, is it?

    Whatever the source of methane, from decaying permafrost or methane hydrates, it was arguably sufficient to end several geological eras, right? 

    Tell me again why I have to meet your criteria before I become alarmed?

    Shouldn't we err on the side of caution, when we're talking about the fate of the biosphere?

    Isn't climate change in general, and warming in the Arctic in particular, occuring much, much more rapidly than predicted? 

    The hydroxyl radical oxidation mechanism which oxidizes methane into CO2 is also impacted by large releases of methane. Isaksen and his collaborators claim the following:

    Strong atmospheric chemistry feedback to climate warming
    from Arctic methane emissions

    It is shown that if global methane emissions were to increase by factors of 2.5 and 5.2 above current emissions, the indirect contributions to RF would be about 250% and 400%, respectively, of the RF that can be attributed to directly emitted methane alone. Assuming several hypothetical scenarios of CH4 release associated with permafrost thaw, shallow marine hydrate degassing, and submarine landslides, we find a strong positive feedback on RF through atmospheric chemistry. In particular, the impact of CH4 is enhanced through increase of its lifetime, and of atmospheric abundances of ozone, stratospheric water vapor, and CO2
    as a result of atmospheric chemical processes

    It's my alarm, Chris.

    I can't be alarmed without your permission?


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  17. Good, useful article. Thanks.One point. How would the graph showing what might happen to a nearly instantaneous pulse of methane change if there was a gradual but significant increase in methane release? Is that more likely?I note that CH4 concentration in the atmosphere is increasing at the moment, following a few years of level concentration. Although methane may be 25 times as powerful as CO2 over 100 years, I understand that it may be as much as 100 times as powerful over a few years. Given that methane concentrations are increasing and, therefore, the degradation rate is not even keeping up with the rate of new releases, never mind exceeding it, isn't the more powerful factor of 100 a more realistic one to use? I'm not sure which factor is used in your estimate of ~0.5 W/m2.
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  18. Leland @16

    The PETM offers an interesting reference point for just how fast methane release might happen. It isn't clear what all the sources of CO2 released during the PETM were - subsea avalanches exposing methane clathrates, Antarctic permafrost, rupturing of Natural Gas deposits near Brazil are all plausible. But we do know something about the rate that CO2 levels changed.

    Lee Kump and his colleagues were able to use a core taken from near Svarlbad to give us an estimate of how fast CO2 levels were rising during the PETM. The rate was 10 times slower than today.

    Even if we assumed that all the observed CO2 rise back then originated 100% as Methane that was oxidised to CO2 it is still only 10% of current emissions of CO2. This suggests that there is an upper limit to how fast Methane will outgas today at less than 10% or so of current CO2 emissions. Particularly since no one is suggesting such dramatic triggers as undersea avalanches as part of the mix today.

    That isn't to say that the long term total emissions of Methane may not be very substantial. Just that there is a speed limit on the rate.

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  19. "undersea avalanches"

    Why shouldn't these be one of the mechanisms by which methane may be suddenly released from the ocean floor. IIRC, the sea bed in the ESAS is not perfectly flat. There are deep 'canyons' where such sudden events may take place. Since the permafrost has been warming gradually over much of the Holocene, and much more rapidly lately, its structure is doubtless less solid than it would otherwise be.


    We have seen warmed ice start to deform this way in the GIS recently.



    And, of course, such weakened ice would also be more susceptible to seismic shocks.


    In any case, there do seem to be potential 'pathways' to consider. The proper thing is to analyze the relative likelihood of each, rather than just sweeping the whole thing under the rug.

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  20. Hi Glenn Tamblin at post # 18-

    It's true that methane hydrate dissociation is an endothermic process and that there may be a rate limit to its release. 

    A lot of the total methane release from the hydrates depends on the total methane hydrate inventory, though - the total amount that exists on the earth. 

    Estimates, as you know, range from about 400 billion metric tons to about 77 trillion metric tons - roughly 440 to 85,000 cubic kilometers.

    That's a big range, Glenn.

    Archer and his collaborators estimate we have something like 4,000 cubic kilometers of methane hydrate, while Dickens and his collaborators talk about a consensus estimate of around 10,000 to 20,000 cubic kilometers. I've seen a paper on the End Triassic which talks about roughly 13,000 cubic kilometers released, rather slowly, which in my mind casts doubt on the lower estimates of total hydrate inventory.

    So, first point, we don't know how much hydrate is down there, on the continental shelves. Multiply a low rate of dissociation by a large hydrate inventory, and one can arrive at a high total methane release. This alone argues that complacency is contraindicated.

    Since we are coming out of a series of ice ages, with low ocean temperatures promoting hydrate stability, we could in fact have massive amounts of hydrate in the global hydrate inventory. And hydrate deposits which are uneconomically thin or scattered and useless to the fossil fuel corporations, not worth mapping, really- might release methane even more rapidly than the economically valuable deposits, because of their scattered and porous nature- especially if they are shallow deposits.

    Some of the papers I've looked at  on hydrate dissociation assume that the convoluted three dimensional hydrate deposits, full of chimneys large enough to show up quite well on sonar, will act like a one or two dimensional model spread uniformly over a two dimensional surface- a highly questionable assumption. Complicated real world processes like convection, convoluted geometry, and chimneys, could make such estimates seriously underestimate the rate of methane release from the hydrates.

    I don't want to bet the future of the biosphere on models of hydrate dissociation which could easily be wrong due to the highly fractured nature of hydrate deposits, often full of chimneys from past release of methane. 

    My conviction is that if we surround the hydrate deposits with warmer water, the deposits will find a way to dissociate, via complicated mechanisms including convection and release of pressure build up of associated free methane gas reservoirs. Undersea landslides are a distinct possibility, especially after substantial methane release has weakened the deposits. So, the landslide phenomenon could be an accelerating process.

    The methane gun hypothesis of mass extinctions requires a trigger mechanism, to set off the hydrates- generally a rapid rise in CO2 is postulated. 

    The fact that our modern triggering event is so much more rapid than past triggering events makes me more alarmed rather than less alarmed. The rate that Lee Kump observed for PETM hydrate dissociation might be characteristic of that event given a much slower triggering event, less severe positive feedback effects, and the methane hydrate geographical distribution at the time.

    Regarding geographical distribution- the location of the East Siberian Arctic Shelf, located as it is under the most rapidly warming region on the planet, is particularly worrisome. Another worrisome thing is the current imbalance in ice distribution with most of the ice located in Antarctica. It seems possible that we could have a full blown methane catastrophe occurring in the north, while Antarctica remains relatively intact. This would slow water rise, which in the past has helped stabilize the hydrates due to a rise in hydrostatic pressure by increased water levels.

    There are times in life when alarm is appropriate, and this is one of those times, I believe.

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  21. Glenn,

    Since the forcing today is much greater today than in the PETM (at least 10 times greater), why do you suppose the methane releases during the PETM are the maximum speed possible?  Since the forcing is so much greater, it stands to reason that the methane release will also be much faster.  Can you explain your argument?

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  22. Michael, #21,

    I agree to an extent - what we are doing here WRT atmospheric composition may be unprecedented in the entire Phanerozoic in terms of rate. On that basis, Chris, are we not comparing apples and oranges? It may be completely irrelevant that nothing like the things Wadhams is concerned about appear to have occurred over the past few glacial-interglacial cycles: nothing within them, apparently at the very l;east, occurred so quickly. One to consider!

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  23. I would like to emphasize a point made by Leland, namely that further increasing atmospheric methane will have significant impacts on atmospheric chemistry. Increased atmospheric methane tends to decrease OH radical abundance and increase ozone abundance under current NOx availability, which increases atmospheric pollutant lifetimes and further stresses ecosystems (via ozone).

    A review paper by Wuebbles and Hayhoe can be found here. The potential changes described in the more recent Isaksen paper cited by Leland are indeed "alarming", wherefore the atmospheric chemistry community does place a priority on how methane sources may change, including due to AGW factors.

    Humans have so far approx. trippled the amount of methane in the troposphere (particularly via meat consumption, rice cultivation, and organic waste dumping; aka via boosting methanogenesis, but also via fossil fuel extraction and use), and more adverse atmospheric chemistry effects of that have so far not occurred due to a rather stable cleansing capacity of our atmosphere (supported by our simultaneous pollution of it with NOx). But as its response is non-linear, an out-of-control increasing methane source strength could be devastating, regardless of its speed.

    Meaning, even if the chances of a rapid release are remote from today's point of view, if there is a large reservoir that could be released to the atmosphere, we should be very concerned about that possibility and take any and all preventive action to stop it from actually doing so, regardless of the speed of release.

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  24. By the way, even if most of the methane doesn't make it into the atmosphere, it could still do the biosphere major harm via ocean acidification, as it oxidizes into CO2 in the oceans.

    I seem to recall seeing a modeling paper of this phenomenon in the Arctic ocean, which predicts that chronic methane release from the hydrates would overwhelm the oceans ability to absorb and oxidize the methane, and lead to more direct venting of methane to the atmosphere.

    There are also suspicions that anoxic oceans could increase their production of NOx, I think.

    As gws said, the atmospheric chemistry effects of methane release have to be considered- but so do the oceanic chemistry effects.

    In his book "Under a Green Sky" Peter Ward talks about the truly catastrophic effects of massive methane release on the oceans, including anoxia and proliferation of strange bacteria. We're not there yet, and have a long way to go before things get that bad.

    But, once it starts, could we stop the process? 

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  25. Thanks for this article. I am now less alarmed by Arctic methane than I was.

    The point, however, is moot: even if the was a likelihood of devastating, rapid injections of methane into the atmosphere, there is precious little we could do about it. The future under BAU CO₂ emissions is projected to be so bad that adding a methane menace does not materially affect the outcome for our civilisation, or for our species. Homo Stupidus stupidus.

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  26. This article was linked on another site. The point was made that it doesn't cover free methane, only hydrates. The commenter had this to say:"The warning [of catastrophic release] is about free methane on the ESAS dissociated by geothermal flux and submersion of the shelf over the last 8,000 years and subsequent warming that has degraded the permafrost cap and the methane is now finding pathways to escape from the seabed to the atmosphere. No hydrate dissociation is required. 1 to 2% of the methane on the ESAS is enough to cause catostrophic warming and that is all free methane, not hydrates.Also, the Hydrate Stability Zone is now down to a depth of 1400 meters. The maximum depth of the ESAS is 100 meters, with an average depth of 50 meters.The latest research is showing not only is the degradation of the relic permafrost providing pathways, but seismic activity on the ESAS is creating fissures that are providing pathways for free methane to escape."Any response, Chris?
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  27. Here are some points I got from Chris's well constructed article:

    We don't know exactly how much methane there is in Siberian shelf.

    We don't know how much of this methane may be stored within the permafrost layer (though we do know that this uppermost layer is the one most vulnerable to warming and melting).

    We don't know whether the massive releases of methane that have been observed are continuations of long-term phenomenon or the beginnings of major feedbacks (this from the first two "Responses from Scientists" who admit that this point is already made by Shakhova).

    ...I am somehow not comforted by any of these unkowns. The inference seems to be that these are not known, so we can safely assume the most benign end of the spectrum. Is that a legitimate scientific approach to unknowns?

    There have been times in the past when temperatures were likely warmer in these areas, but those were also times when sea level was rising rapidly, and methane stability depends on both temperature and pressure (and presumably salinity plays some role, which presumably would have been lowered during the same period with water flowing in from melting ice sheets.

    I certainly hope that the conclusion is right: that we are not likely to see massive rapid increases in release of methane from the Arctic sea bed any time soon.

    But many of the main points intended to support such a certainty do not seem particularly...certain.


    Thanks again for the important discussion (and no less a climatologist than Michael Mann has said that it is important to have discussions about the possibility of rapid increases in methane release from ocean bed hydrates).

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  28. Andrea Silverthorne writes:

    Natural gas is methane gas.

    The T. Boone Pickens' of the world have created a terrible monster. The release of methane into our atmosphere has increased geometrically compared to CO2.  Add to this that the method used to make methane in the earth...shale formations, requires 5 mil. gals of water mixed with a carcinogenic cocktail of chemicals for each well they drill. Only 10% of the water is recovered. The rest mixes with natural carbon to create even more CH4.

    (This exessive use of water is why there's a growing dust bowl in the West and N.West, S. West and wherever they drill for oil and gas. Google Dust bowl.)

    Then, if the CH4 is not completely oxidized to CO2 and remains at its first oxidant HCHO formaldehyde, the HCHO contributes to soft tissue evisceration in man and beast. Ergo, bees disappearing, mass fish and bird kills and over the past five to seven years endemic outbreaks in children of nose bleeds and asthma, and an increase in autism. HCHO hides in shallow water, caves, and dew. It is heavier than air and flows along the ground and into open widows and crawls along floors.

    You have people out there who have millions and millions of reams of what they call facts and they spin this kind of web of half-truths and misinterpreted truths and lies, and it’s very difficult for a lay person to go through them. So I try to leave that kind of thing to the scientific community, who are really steeped in scientific literature.

    But just having one of these kinds of arguments, unfortunately, people like me and you and those of us who feel like this is really a big problem that we are criminally negligent in not addressing, have kind of lost that public debate right now. And that’s really scary I think, to be honest.” That’s the word I would use, not just depressing but downright scary. There happens to be one side, on the scientific front, that’s just unassailable.  

    So let us apply our ethical standards to telling the whole scientific story about the formation of methane hydrates; its formation only with fresh water not sea water unless that water is saturated with methane and over a very short time forms Pingoes.  We can carbon date Pingo material to prove that Pingoes never existed in the Beaufort Sea, the Arctic Tundra or elsewhere before 180 years ago. Oil and gas drilling use of fresh water needs through examination as the only source of methane hydrate, CO2 saturation and exess formaldehyde in our world.

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    Moderator Response:

    [DB] Fixed font issues.

  29. One more point/set ofquestions:

    Hasn't this been a particularly long interglacial?

    Doesn't that mean that the relative warmth from this long period has had thousands of years now to penetrate deep into the permafrost?

    Doesn't that likely make the permafrost more susceptible now to sudden shocks like seismic activity...than it has been in the past, both during the Holocene and during other, shorter interglacials?

    Thanks ahead of time for any light anyone can throw on any of these areas.

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  30. People should take the post by Potomac Oracle with a grain of salt since it is scientifically incoherent. Note that the site that it was referenced from is full of anti-vaccine nonsense

    I was taken, though, with the image of formaldehyde crawling along the floor into "open widows". 

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  31. TonyW@26

    Indeed there is gas seeping to the surface from deep sources on the ESAS. A paper by Cramer and Franke (2005) documented this very nicely, with sea-bed samples, gas analyses and deep seismic reflection data. I really do not know why this paper is not cited more widely, since it seems to me to be much more through and detailed than subsequent papers on the ESAS.

    Yes, the methane migrates up gas chimneys through the permafrost, some of which are related to faults. However, this gas release is slow and steady, as evidenced by the fact that it is still ongoing in deeper-water parts of the shelf in the northern Laptev Sea, where there is no permafrost. It might well be the case that melting of the permafrost cap will eventually perforate it in places where it is currently continuous, but this will take time and even when it happens, what we will end up with is what we see in the N Laptev Sea and not a sudden outburst.

    Here's a section from the Cramer and Franke paper, showing gas chimneys, deep structure and permafrost in the central Laptev Sea:

    I have written about sub-cap methane in a series of SkS articles: Part1, Part2, Part3 and Part4. In the last one, I speculate on the origin of methane on the ESAS and give my (blogger's) assessment of the relative importance and timing of GHG emissions resulting from a thawing cryosphere.  I think that the one we have to worry about most in this century is the thawing of onshore permafrost and the emissions of CO2 and CH4 that will come from biodegradation of thawed organic matter. There will be some additional releases of thermogenic methane coming from perforation of permafrost caps on land and in shallow seas, but the quantities and the timing of these releases is uncertain. Emissions from hydrates in the deep sea, under and within permafrost and (maybe) under ice sheets, may well prove substantial over longer timescales.

    I would have had no problem with the Whiteman et al article if they had portrayed it as a what-if model of an unlikely worst-case-imaginable scenario. But they did not qualify it that way, instead they wrote (my emphasis, references removed):

    As the amount of Arctic sea ice declines at an unprecedented rate the thawing of offshore permafrost releases methane. A 50-gigatonne (Gt) reservoir of methane, stored in the form of hydrates, exists on the East Siberian Arctic Shelf. It is likely to be emitted as the seabed warms, either steadily over 50 years or suddenly. Higher methane concentrations in the atmosphere will accelerate global warming and hasten local changes in the Arctic, speeding up sea-ice retreat, reducing the reflection of solar energy and accelerating the melting of the Greenland ice sheet. The ramifications will be felt far from the poles.

    which I think is irresponsible.

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  32. About the graph of the single large release in the original article-

    Nice graph. It's somewhat reassuring, actually, visually.

    But how does it correspond to reality?

    What if that single large release of methane sets off additional releases, of various magnitudes, via increased greenhouse forcing and stimulation of both chronic and large scale individual releases?

    What if that large release severely degrades the hydroxyl radical oxidation mechanism, and causes additional greenhouse forcing and a slower return to chronic methane release behavior?

    What if those atmospheric chemistry effects leading to increased forcing, as postulated by Isaksen's modeling, set off additional methane releases?

    Why should we limit ourselves to a single large release event scenario, when each large release could both amplify chronic releases and possibly stimulate additional large releases, via positive feedback?

    What if increases in both CO2 and methane concentrations lead to higher temperatures, increasing water vapor concentrations, amplifying the combined effects of all the greenhouse gases on radiative forcing? This postive correlation between CO2 concentration and water vapor concentration is well accepted by most climate scientists.

    The methane concentration graph that results could look like a jagged series of peaks, climbing up, and up, and up...

    And not come down...for maybe a hundred thousand years, as apparently happened during other possible methane catastrophes, such as the End Permian.

    Life could regain its former several tens of millions of years.

    Except that the sun is hotter now, than it was during the End Permian, by maybe two or thee percent- an effect that James Hansen says is equivalent in forcing to around a thousand ppm of CO2.

    Apparently James Hansen has a new paper coming out, which I have not yet been able to gain access to on the web. The Guardian reports (July of this year):

    The world is currently on course to exploit all its remaining fossil fuel resources, a prospect that would produce a "different, practically uninhabitable planet" by triggering a "low-end runaway greenhouse effect." This is the conclusion of a new scientific paper by Prof James Hansen, the former head of NASA's Goddard Institute for Space Studies and the world's best known climate scientist.

    The paper due to be published later this month by Philosophical Transactions of the Royal Society A (Phil. Trans. R. Soc. A) focuses less on modeling than on empirical data about correlations between temperature, sea level and CO2 going back up to 66 million years.

    Given that efforts to exploit available fossil fuels continue to accelerate, the paper's principal finding - that "conceivable levels of human-made climate forcing could yield the low-end runaway greenhouse effect" based on inducing "out-of-control amplifying feedbacks such as ice sheet disintegration and melting of methane hydrates" - is deeply worrying.

    The paper projects that global average temperatures under such a scenario could eventually reach as high as between 16C and 25C over a number of centuries. Such temperatures "would eliminate grain production in almost all agricultural regions in the world", "diminish the stratospheric ozone layer", and "make much of the planet uninhabitable by humans."

    Hansen seems to think destabilization of the hydrates via a mixture of chronic and multiple large releases over several centuries is a realistic possibility, with final effects far beyond what Chris Colose or David Archer and his collaborators think is possible.

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  33. Will – Thanks for the ref. to interview with Dr Shakhova Deweaver

    @ 9. – on your point 3: When onshore permafrost melts from the surface down, underlying permafrost inhibits drainage with the result that shallow water covered surfaces are produced. Methane produced beneath the water-table in anoxic conditions vents directly to the atmosphere unoxidised.

    However, CH4 produced in the presence of oxygen, particularly where sphagnum moss is present, are largely oxidized and enter the atmosphere as CO2. It can be concluded from this that during early stages of permafrost loss most methane produced as a result of permafrost loss will enter the atmosphere as CH4 but as loss continues at greater depth and surface drainage occurs CH4 will be increasingly oxidized to CO2. Lawrence et al (2005) estimate that permafrost covering ~9.5m km2 will have thawed to a depth of 3 meters by 2100.

    On your point 4: Most of the Siberian continental shelf is covered by water ≤ 50 metres deep. Methane escaping from the seabed vents to the surface through a water column which is too shallow to bring about any oxidation before it reaches the sea surface and enters the atmosphere. For CH4 escaping from the seabed to oxidize a water column of at least 200 metres is required. Methane escaping from the seabed west of Svalbad from depths of 200-400 metres is very largely but not fully oxidized or absorbed by ocean water before reaching the surface but even from these depths some CH4 is present at the surface.

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  34. Nafeez Ahmed has just responded to what he calls "Skeptical Science's unusually skewered analysis"  in this new Guardian article.  

    It seems to me that when it comes to Arctic methane there's much uncertainty, and the wise course is to hope for the best but plan for the worst. Having strong opinions on this particular issue is backing oneself into a corner.

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  35. Nafeez Ahmed's response in the Guardian is well worth reading.

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  36. Thanks for the comments everyone.

    I've seen the Guardian's most recent response.  I still think it conflates many different issues, including varying sources of CH4 releases (e.g., in his point #7, the 2009 Science paper he references with respect to the Younger Dryas are talking about wetlands, not hydrate destabilization), and still presents no evidence for a significantly new Arctic methane source to the atmosphere....again, observed methane emissions around the Arctic are not evidence that they are a new source.  The point #4 about highest CH4 levels in 800k is due to direct anthropogenic activity, not hydrate destabilization, and renewed growtth in atmospheric CH4 has been attributed to a few different factors (Dlugokencky has recent literature on this).  If a positive hydrate feedback exists, it is currently very small and not emerging clearly.

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  37. Also with reference to the Guardian article, the claims that the Arctic was not ice free in the summer during at least part of the Eemian are very likely wrong.  I base that claim on the facts that there is solid evidence that the Arctic was ice free in summer durring the Holocene Climactic Optimum when temperatures were comparable with current temperatures, but major ice sheets persisted, such that albedo forcing in the Arctic was less than currently.  Further, current temperatures are sufficiently high (or very close) to force an ice free summer.  The Eemian had a more extended period that was at least as warm as current temperatures, and those of the HCO and more likely than not, was slightly warmer.  Given that, it is implausible that the Arctic was not ice  free in summer during at least part of the Eemian.

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  38. None of the references in the Guardian article point to observations of shallow gas hydrates on the ESAS. There are shallow gas hydrates (around 60 metres depth) reported in Yamal, some 2000 km away, but those are (according to the author) relict hydrates thought to have been formed when that area was overlaid by an icesheet (or a marine transgression) and have been preserved in a metastable form after disappearence of the icesheet (or regression of the sea). As far as I know, nobody has proposed those kinds of events in this part of eastern Siberia. On the contrary, the local sea level on the ESAS has risen since the last glacial maximum, submerging the permafrost that formed when the shelf was exposed land.

    All of the references cited show that hydrates form below 200 metres depth in areas of permafrost. The Shakhova et al 2010 paper does not present any geophysical or sampling evidence for hydrates above 200m on the ESAS. Permafrost, yes, gas leaks yes, but not shallow hydrates.

    There's little doubt that a warming climate will provide huge carbon cycle feedbacks in the Arctic, from both carbon dioxide and methane.  MacDougall, Avis and Weaver have showed that, by the end of the century, feedbacks from thawing land permafrost will increase temperatures by 0.25 to 1.0 degree Celsius from carbon dioxide emissions alone. That's 174 billion tonnes of carbon emissions over the next several decades in their median case.  For me, that's more worrying than conjectural methane eruptions from the ESAS. Having said that, I will be following the future research results there with interest and anxiety.

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  39. Apparently, Shakhova and Semiletov have a paper to be published soon, in Nature. They seem very concerned about abrupt methane releases, so I'm sure that the paper will present more discussion points.

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  40. Here is a link to Hansen's paper, the one that says that a low level runaway heating scenario is possible, if we burn all of the fossil fuels:

    Climate Sensitivity, Sea Level, and Atmospheric CO2

    There's a good summary of Hansen's perception of the methane hydrate problem included in that paper.

    I don't think his model includes atmospheric chemisty effects as postulated by Isaksen's modeling. These atmospheric chemistry effects including increased stratospheric water vapor, increased tropospheric ozone, and increased methane lifetime due to the exhaustion of the hydroxyl radical oxidation mechanism would likely make the low level runaway worse than Hansen's modeling suggests, I think.

    What would result?

    A more severe low level runaway, or something even worse?

    A mostly uninhabitable planet, or an entirely uninhabitable planet?

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  41. Here's a quote from Hansen's paper linked to above, which claims that a low level runaway greenhouse, making most of the planet uninhabitable, is probable if we burn all of the fossil fuels:

    The potential carbon source for hyperthermal warming that received most initial attention was methane hydrates on continental shelves, which could be destabilized by sea floor warming (Dickens et al., 1995). Alternative sourcesinclude release of carbon from Antarctic permafrost and peat (DeConto et al., 2012). Regardless of the carbon source(s), it has been shown that the hyperthermals were astronomically paced, spurred by coincident maxima in Earth's orbit eccentricity and spin axis tilt (Lourens et al., 2005), which increased high latitude insolation and warming. The PETM was followed by successively weaker astronomically-paced hyperthermals, suggesting that the carbon source(s) partially recharged in the interim (Lunt et al., 2011). A high
    temporal resolution sediment core from the New Jersey continental shelf (Sluijs et al., 2007) reveals that PETM warming in at least that region began about 3000 years prior to a massive release of isotopically light carbon. This lag and climate simulations (Lunt et al., 2010a) that produce large warming at intermediate ocean depths in response to initial surface warming are consistent with the concept of a methane hydrate role in hyperthermal events.

    Hansen limits himself here to discussing the PETM, a hyperthermal event from about 50 million years ago, and the decreasing series of hyperthermal events that followed it. As Dickens points out, this behaviour is consistent with the hydrates behaving like an electronic capacitor, charging and then discharging in a decreasing series as the deposits become more and more depleted.

    But there have in fact been a series of such mass extinction events associated with carbon isotope signatures perfectly matching an influx of several trillion tons of C13 enriched methane from the methane hydrates into the atmosphere. Canditate events for the methane catastrophe hypothesis include the End Permian, the End Triassic, and the PETM.

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  42. Whoops, make that C13 depleted carbon (C12 enriched), in the last paragraph above.

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  43. Does Freshwater Runoff in the Arctic change Ocean Circulation to Unlock Methane Hydrate in the Deep Ocean? (LINK)

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    Moderator Response:

    [DB] Condensed link.

  44. Even if there are a series of past mass extinctions associated with carbon isotope excursions suggestive of massive methane release from the hydrates, there is still the question of rate- how rapidly did these events occur?

    Here's a paper from a location in China, which has a particularly high resolution stratigraphic record of the PETM.

    High-resolution carbon isotope record for the Paleocene-Eocene thermal maximum from the Nanyang Basin, Central China

    Their calculated duration of the first large probable methane release during the PETM?

    Less than 210 years:

    The δ13C record from the Nanyang Basin thus represents the highest resolution PETM record available to date, thus facilitating detailed investigations into the PETM event. In the Nanyang record, the PETM was triggered within a 2 cm interval, indicating that its onset occurred in less than 210 years. This favors the hypothesis that the PETM was caused by a massive release of methane hydrate (δ13C =–60‰) from the continental slope. Other hypotheses for carbon release, such as decomposition of rich organic sediments, burning of peat land and tectonic processes, would have led to a slow carbon release rather than a rapid emission.

    The authors go on to discuss various explanations for the initial carbon isotope spike triggering the PETM, including global warming, but conclude that a catastrophic event such as a massive earthquake and submarine landslide must have been responsible for the initial massive release. Magmatic intrusion from flood basalt eruptions might also qualify as a catastrophic event. They do discuss the subsequent further slow decline in C13 ratios, and say that that slower decline may be due to subsequent methane release from the hydrates stimulated by positive feedback.

    But, there were a subsequent series of hyperthermal events, after the PETM, as discussed by Hansen. Those events apparently associate with orbital changes and so with orbital driven global warming.

    Were those subsequent hyperthermal events also due to catastrophic events? This does not seem very likely, to me- that a series of catastrophic events timed to orbital cycles would occur.

    This subsequent decreasing series of smaller hyperthermal events appears to be tied to orbital changes in insolation, and so to global warming.

    So why did orbital variations in insolation trigger this declining series of probable methane hydrate releases?

    Perhaps there was a shallow region of permafrost bound hydrates near one of the poles, capable of being triggered by global warming... perhaps like our own East Siberian Arctic Shelf (ESAS).

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  45. Here's an interesting paper, on the PETM and the series of smaller Eocene hyperthermal events with accompanying carbon isotope excurstions that followed it, called in this paper the ETM2 and ETM3 events:

    Past extreme warming events linked to massive carbon release from thawing permafrost

    The authors present seemingly convincing correlations between the ETM2 and ETM3 events and orbital variations in insolation. They suggest a negative correlation with CaCO3 content of sediments during a series of orbital variations surrounding and including these events.

    They claim that high latitude melting of permafrost and associated positive feedbacks are the likely cause of these hyperthermal events.

    Unfortunately, other authors claim that the PETM (called ETM1 in this paper) and the other Eocene events have similar C13 and O18 excursion correlations, which demonstrate that the carbon source is similar or identical.

    And, the initial sharp phase of the PETM/ETM1 occurred very rapidly, in less than about 200 years- seeingly too rapidly for any other explanation except methane hydrate release.

    So, if the PETM/ETM1 was a hydrate release event, and the other events have matching C13 and O18 isotope excursions, then ETM2, ETM3 were also likely mainly methane release events, I think.

    So, we are arguably left with a series of orbital climate change driven methane releases.

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  46. Here's Paul Beckwith's response to this SKS article:

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  47. Paul Beckwith's response as a link.

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  48. We should not forget that our future course of action- whether to massively switch to renewable energy sources or continue on our fossil fuel trajectory- is an economic problem as well as a scientiic problem.

    The methane in the methane hydrates is worth hundreds of billions, perhaps trillions of dollars.

    The methane in the methane hydrates could also arguably kill the biosphere.

    A scientific paper which mentions the economic factors associated with the methane hydrate problem is linked to below:

    Gas hydrates: entrance to a methane age or climate threat?

    Methane hydrates, ice-like compounds in which methane is held in crystalline cages formed by water molecules, are widespread in areas of permafrost such as the Arctic and in sediments on the continental margins. They are a potentially vast fossil fuel energy source but, at the same time, could be destabilized by changing pressure–temperature conditions due to climate change, potentially leading to strong positive carbon–climate feedbacks. To enhance our understanding of both the vulnerability of and the opportunity provided by methane hydrates, it is necessary (i) to conduct basic research that improves the highly uncertain estimates of hydrate occurrences and their response to changing environmental conditions, and (ii) to integrate the agendas of energy security and climate change which can provide an opportunity for methane hydrates—in particular if combined with carbon capture and storage—to be used as a ‘bridge fuel’ between carbon-intensive fossil energies and zero-emission energies. Taken one step further, exploitation of dissociating methane hydrates could even mitigate against escape of methane to the atmosphere. Despite these opportunities, so far, methane hydrates have been largely absent from energy and climate discussions, including global hydrocarbon assessments and the Fourth Assessment Report of the Intergovernmental Panel on Climate Change.

    Intense localized methane plumes could perhaps be captured, burned using (for example) oxyfuel combustion to generate electricity, and the resulting CO2 deep injected into fractured basalt sediments, I think. The resulting electricity could be transmitted to shore using submarine electrical cables- a new but farily well developed technology. This would be carbon neutral remediation of the captured methane, if it works.

    On the other hand, trying to capture the methane would be like trying to catch soup in a net, in my opinion. Vast quantities of methane would go into the oceans, contributing to ocean acidification, leading to probable widespread anoxic areas, and perhaps even a dead arctic ocean- one incapable of oxidizing much of the methane released into it by the hydrates, according to modeling by the DOE/LBNL/LANL modeling done by the IMPACTS (Investigation of the Magnitudes and Probabilities of Abrupt Climate TransitionS (IMPACTS)) group. Check out their publications link:

    Investigation of the Magnitudes and Probabilities of Abrupt Climate TransitionS (IMPACTS) Project

    As an inhabitant of the Earth, I don't think that a "methane age" of abundant energy is worth the risk of low level or greater runaway destabilization of the climate system.

    Fossil fuel corporation executives and major stockholders of fossil fuel corporations may disagree. 

    In such an environment, there is the potential for enormous profits to skew the scientific debate. 

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  49. Have we been looking at Climate Sensitivity all wrong? We've been focused on global temperature sensitivity to CO2 doubling, but shouldn't we have been focusing on global temperature sensitivity to input radiative forcing? Atmospheric methane increases occurred in the ice-core data in tandem with temperature increases with just a 0.5W/m2 increase in input radiative forcing due to the Milankovitch cycle. The resulting feedback exacerbated the rise in temperature to around 5degC. Why should the planet's store of methane now NOT react when humanity has created a 3W/m2 increase in input radiative forcing (minus the aerosol component) by burning fossil fuels and deforesting the planet?

    I don't understand this "what me worry" attitude among prominent climate scientists on the methane issue. Is it subconsciously linked to their consumption of beef?

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  50. The Department of Energy and national labs IMPACTS group is attempting to quantitatively model sudden climate change scenarios, including methane hydrate release. 

    Here are some links to one of their papers, doing basin scale modeling of the next hundred years of methane hydrate release, and also a slide show based on that paper:


    Basin-Scale Assessment of Gas Hydrate Dissociation in Response to Climate Change

    The second link is to a slide show, based on the scientific paper linked to by the first link.

    Their assumptions are troubling in some respects, at least to me. They use slab models- one dimensional models projected over a two dimenstional surface- and suggest that their modeling confirms that the dissociation process will be gradual and orderly. But the use of slab models dictates that the process will be orderly, I think, which seems like circular reaoning to me. Will it really be an orderly process, and what are we willing to risk to confirm that? 

    I believe that they are assuming a total methane hydrate inventory of around 4000 cubic kilometers of methane hydrate. I wonder, myself, what their modeling would tell us if they were to use the higher global methane hydrate inventory estimates of around 80,000 cubic kilometers.

    But, still, it seems like a good first effort, I think. 

    Their modeling seems to show some interesting or perhaps terrifying things. Their conclusions?

    • Shallow hydrates can release significant methane rapidly, with significant methane fluxes regulated by coupled thermo-hydrological processes

    • Methane is relevant to ocean (and atmospheric!) chemistry, not just as a contributor to total atmospheric CO2
    • 1-D models averaged over depth/temperature/area can estimate basin-scale release potential
    • The vast majority of deep hydrates are stable, in the short term, but the methane release potential is still large
    • Limited instability/release can feed biochemical/chemical changes in the ocean and atmosphere, before climate effects are considered
    • Resource limitations overturn assumptions about methane oxidation
    • New coupled seafloor-ocean-atmosphere calculations under way (with plume physics, extended biochemistry, higher resolution) leading to a coupled global model… and better estimates.

    Their conservative modeling, which postulates an orderly process, shows significant Arctic Ocean anoxia after 30 years of methane releases from the hydrates, with one figure suggesting a 60% direct transfer to the atmosphere through these anoxic waters. Their conservative modeling arrives at numbers like an additional 800 ppb of methane in the tropics, rising to an additional 1,800 ppb in the Arctic, after 30 years of methane release. So,assuming that methane concentrations, mostly from other sources, rise to about 2000 ppb in 30 years, that would mean methane concentrations of about 2800 ppb at the equator, increasing to 3,600 ppb in the Arctic.

    But I don't think that their modeling takes into account increased warming from the methane itself, and a subsequent higher methane release rate. I don't think that their modeling takes into account what would happen if the global methane hydrate inventory turns out to be 80,000 cubic kilometers of methane hydrate, rather than 4,000 cubic kilometers. I don't think that their modeling takes into account atmospheric chemistry effects predicted by Isaksen's modeling, increasing methane lifetime and so increasing its greenhouse effect. Their modeling suggests an orderly top down methane release process- but what if that projected order is an artifact of their use of slab models? 

    Their modeling also does not consider shallow permafrost bound hydrates- for example those contained in the East Siberian Arctic shelf.

    One of their papers shows a huge anoxic area- not in the Arctic Ocean, but in the northern pacific in the region of the Sea of Othosk. Their modeling suggests that the Sea of Othosk is particularly vulnerable to sea water warming, and could "light up like a candle".

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