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Much ado about methane

Filed under: — david @ 4 January 2012

Methane is a powerful greenhouse gas, but it also has an awesome power to really get people worked up, compared to other equally frightening pieces of the climate story.

What methane are we talking about?

The largest methane pools that people are talking about are in sediments of the ocean, frozen into hydrate or clathrate deposits (Archer, 2007). The total amount of methane as ocean hydrates is poorly constrained but could rival the rest of the fossil fuels combined. Most of this is unattractive to extract for fuel, and mostly so deep in the sediment column that it would take thousands of years for anthropogenic warming to reach them. The Arctic is special in that the water column is colder than the global average, and so hydrate can be found as shallow as 200 meters water depth.

On land, there is lots of methane in the thawing Arctic, exploding lakes and what not. This methane is probably produced by decomposition of thawing organic matter. Methane could only freeze into hydrate at depths below a few hundred meters in the soil, and then only at “lithostatic pressure” rather than “hydrostatic”, meaning that the hydrate would have to be sealed from the atmosphere by some impermeable layer. The great gas reservoirs in Siberia are thought to be in part frozen, but evidence for hydrate within the permafrost soils is pretty thin (Dallimore and Collett,1995)

Russian gas well

Is methane escaping due to global warming?

There have been observations of bubbles emanating from the sea floor in the Arctic (Shakhova, 2010; Shakhova et al., 2005) and off Norway (Westbrook, 2009). The Norwegian bubble plume coincides with the edge of the hydrate stability zone, where a bit of warming could push the surface sediments from stable to unstable. A model of the hydrates (Reagan, 2009) produces a bubble plume similar to what’s observed, in response to the observed rate of ocean water warming over the past 30 years, but with this warming rate extrapolated further back in time over the past 100 years. The response time of their model is several centuries, so pre-loading the early warming like they did makes it difficult to even guess how much of the response they model could be attributed to human-induced climate change, even if we knew how much of the last 30 years of ocean warming in that location came from human activity.

Sonar images of methane plumes, from Westbrook

Lakes provide an escape path for the methane by creating “thaw bulbs” in the underlying soil, and lakes are everywhere appearing and disappearing in the Arctic as the permafrost melts. (Whether you get CO2 or a mixture of CO2 plus methane depends critically on water, so lakes are important for that reason also.)

Methane bubbles captured in freezing lake ice in Alaska

So far there hasn’t been strong evidence presented for detection enhanced methane fluxes due to anthropogenic warming yet. Yet it is certainly believable for the coming century however, which brings us to the next question:

What effect would a methane release have on climate?

The climate impact of releasing methane depends on whether it is released all at once, faster than its lifetime in the atmosphere (about a decade) or in an ongoing, sustained release that lasts for longer than that.

chronic vs catastrophic release cartoon

When methane is released chronically, over decades, the concentration in the atmosphere will rise to a new equilibrium value. It won’t keep rising indefinitely, like CO2 would, because methane degrades while CO2 essentially just accumulates. Methane degrades into CO2, in fact, so in simulations I did (Archer and Buffett, 2005) the radiative forcing from the elevated methane concentration throughout a long release was about matched by the radiative forcing from the extra CO2 accumulating in the atmosphere from the methane as a carbon source. In the figure below, the dashed lines are from a simulation of a fossil fuel CO2 release, and the solid lines are the same model but with an added methane hydrate feedback. The radiative forcing from the methane combines the CH4 itself which only persists during the time of the methane release, plus the added CO2 in the atmosphere, which persists throughout the simulation of 100,000 years.

response of carbon cycle / hydrate model to fossil fuel CO2 forcing

The possibility of a catastrophic release is of course what gives methane its power over the imagination (of journalists in particular it seems). A submarine landslide might release a Gigaton of carbon as methane (Archer, 2007), but the radiative effect of that would be small, about equal in magnitude (but opposite in sign) to the radiative forcing from a volcanic eruption. Detectable perhaps but probably not the end of humankind as a species.

What could happen to methane in the Arctic?

The methane bubbles coming from the Siberian shelf are part of a system that takes centuries to respond to changes in temperature. The methane from the Arctic lakes is also potentially part of a new, enhanced, chronic methane release to the atmosphere. Neither of them could release a catastrophic amount of methane (hundreds of Gtons) within a short time frame (a few years or less). There isn’t some huge bubble of methane waiting to erupt as soon as its roof melts.

And so far, the sources of methane from high latitudes are small, relative to the big player, which is wetlands in warmer climes. It is very difficult to know whether the bubbles are a brand-new methane source caused by global warming, or a response to warming that has happened over the past 100 years, or whether plumes like this happen all the time. In any event, it doesn’t matter very much unless they get 10 or 100 times larger, because high-latitude sources are small compared to the tropics.

Methane as past killing agent?

Mass extinctions like the end-Permean and the PETM do typically leave tantalizing spikes in the carbon isotopic records preserved in limestones and organic carbon. Methane has an isotopic signature, so any methane hijinks would be recorded in the carbon isotopic record, but so would changes in the size of the living biosphere, soil carbon pools such as peat, and dissolved organic carbon in the ocean. The end-Permean extinction is particularly mysterious, and my impression is that the killing mechanism for that is still up for grabs. Methane is also one of the usual suspects for the PETM, which consisted of about 100,000 years of isotopically light carbon, which is thought to be due to release of some biologically-produced carbon source, similar to the way that fossil fuel CO2 is lightening the carbon isotopes of the atmosphere today, in concert with really warm temperatures. I personally believe that the combination of the carbon isotopes and the paleotemperatures pretty much rules out methane as the original carbon source (Pagani et al., 2006), although Gavin draws an opposite conclusion, which we may hash out in some future post. In any case, the 100,000-year duration of the warming means that the greenhouse agent through most of the event was CO2, not methane.

Could there be a methane runaway feedback?.

The “runaway greenhouse effect” that planetary scientists and climatologists usually call by that name involves water vapor. A runaway greenhouse effect involving methane release (such as invoked here) is conceptually possible, but to get a spike of methane concentration in the air it would have to released more quickly than the 10-year lifetime of methane in the atmosphere. Otherwise what you’re talking about is elevated methane concentrations, reflecting the increased source, plus the radiative forcing of that accumulating CO2. It wouldn’t be a methane runaway greenhouse effect, it would be more akin to any other carbon release as CO2 to the atmosphere. This sounds like semantics, but it puts the methane system into the context of the CO2 system, where it belongs and where we can scale it.

So maybe by the end of the century in some reasonable scenario, perhaps 2000 Gton C could be released by human activity under some sort of business-as-usual scenario, and another 1000 Gton C could come from soil and methane hydrate release, as a worst case. We set up a model of the methane runaway greenhouse effect scenario, in which the methane hydrate inventory in the ocean responds to changing ocean temperature on some time scale, and the temperature responds to greenhouse gas concentrations in the air with another time scale (of about a millennium) (Archer and Buffett, 2005). If the hydrates released too much carbon, say two carbons from hydrates for every one carbon from fossil fuels, on a time scale that was too fast (say 1000 years instead of 10,000 years), the system could run away in the CO2 greenhouse mode described above. It wouldn’t matter too much if the carbon reached the atmosphere as methane or if it just oxidized to CO2 in the ocean and then partially degassed into the atmosphere a few centuries later.

The fact that the ice core records do not seem full of methane spikes due to high-latitude sources makes it seem like the real world is not as sensitive as we were able to set the model up to be. This is where my guess about a worst-case 1000 Gton from hydrates after 2000 Gton C from fossil fuels in the last paragraph comes from.

On the other hand, the deep ocean could ultimately (after a thousand years or so) warm up by several degrees in a business-as-usual scenario, which would make it warmer than it has been in millions of years. Since it takes millions of years to grow the hydrates, they have had time to grow in response to Earth’s relative cold of the past 10 million years or so. Also, the climate forcing from CO2 release is stronger now than it was millions of years ago when CO2 levels were higher, because of the band saturation effect of CO2 as a greenhouse gas. In short, if there was ever a good time to provoke a hydrate meltdown it would be now. But “now” in a geological sense, over thousands of years in the future, not really “now” in a human sense. The methane hydrates in the ocean, in cahoots with permafrost peats (which never get enough respect), could be a significant multiplier of the long tail of the CO2, but will probably not be a huge player in climate change in the coming century.

Could methane be a point of no return?

Actually, releasing CO2 is a point of no return if anything is. The only way back to a natural climate in anything like our lifetimes would be to anthropogenically extract CO2 from the atmosphere. The CO2 that has been absorbed into the oceans would degas back to the atmosphere to some extent, so we’d have to clean that up too. And if hydrates or peats contributed some extra carbon into the mix, that would also have to be part of the bargain, like paying interest on a loan.

Conclusion

It’s the CO2, friend.


References

  1. D. Archer, "Methane hydrate stability and anthropogenic climate change", Biogeosciences, vol. 4, pp. 521-544, 2007. http://dx.doi.org/10.5194/bg-4-521-2007
  2. N. Shakhova, I. Semiletov, I. Leifer, A. Salyuk, P. Rekant, and D. Kosmach, "Geochemical and geophysical evidence of methane release over the East Siberian Arctic Shelf", Journal of Geophysical Research, vol. 115, 2010. http://dx.doi.org/10.1029/2009JC005602
  3. N. Shakhova, "The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle", Geophysical Research Letters, vol. 32, 2005. http://dx.doi.org/10.1029/2005GL022751
  4. G.K. Westbrook, K.E. Thatcher, E.J. Rohling, A.M. Piotrowski, H. Pälike, A.H. Osborne, E.G. Nisbet, T.A. Minshull, M. Lanoisellé, R.H. James, V. Hühnerbach, D. Green, R.E. Fisher, A.J. Crocker, A. Chabert, C. Bolton, A. Beszczynska-Möller, C. Berndt, and A. Aquilina, "Escape of methane gas from the seabed along the West Spitsbergen continental margin", Geophysical Research Letters, vol. 36, pp. n/a-n/a, 2009. http://dx.doi.org/10.1029/2009GL039191
  5. M.T. Reagan, and G.J. Moridis, "Large-scale simulation of methane hydrate dissociation along the West Spitsbergen Margin", Geophysical Research Letters, vol. 36, 2009. http://dx.doi.org/10.1029/2009GL041332
  6. D. Archer, and B. Buffett, "Time-dependent response of the global ocean clathrate reservoir to climatic and anthropogenic forcing", Geochemistry, Geophysics, Geosystems, vol. 6, pp. n/a-n/a, 2005. http://dx.doi.org/10.1029/2004GC000854
  7. M. Pagani, K. Caldeira, D. Archer, and J.C. Zachos, "ATMOSPHERE: An Ancient Carbon Mystery", Science, vol. 314, pp. 1556-1557, 2006. http://dx.doi.org/10.1126/science.1136110

148 Responses to “Much ado about methane”

  1. 1
    Anonymous Coward says:

    Much needed post in view of the lurid alarmism making the rounds.
    Thanks David!

  2. 2
    Geoff Beacon says:

    I am sceptical of climate models (but see their uses as guidelines):

    Haven’t they been underestimating several effects of climate change? (e.g. loss of Arctic sea ice?)

    Aren’t they missing important climate feedbacks? (e.g. CO2 and CH4 feedbacks from the Arctic, drying of the Amazon basin &etc.)

    Aren’t they lulling policy makers into a false sense of security.

    One Arctic expert said to me recently “If there’s a conflict between reality and models, the modelers stick to their models.”

    Reality seems much more serious than the models have predicted.

    Did Natalia Shakhova and Igor Semiletov really see much bigger plumes of methane this year than two years ago? If they did would be strange that 10000 year old warming should now be causing it.

    The links to the (satellite?) images in wili’s post on the last open thread are interesting:

    Here are two maps comparing methane levels above the Arctic in November 2010 and 2011:

    ftp://asl.umbc.edu/pub/yurganov/methane/MAPS/NH/ARCTpolar2010.11._AIRS_CH4_400.jpg

    ftp://asl.umbc.edu/pub/yurganov/methane/MAPS/NH/ARCTpolar2011.11._AIRS_CH4_400.jpg

    They seem to show large recent increases in methane and don’t seem like nonsense, perhaps they are.

    What worries me was the lack of “official” RealClimate comment on

    – the undershoot of the models
    – the missing feedbacks
    – the observations of the methane plumes or
    – the satellite images.

    [Response:I'm with you on models in general, they often underpredict observations (ice sheet models, for example), often because they miss feedback, and they surely should be trumped by data where it's available. But there's so much more methane coming from the tropics that even if the high latitudes did start really pumping, they wouldn't have much impact until they start to rival the tropics, which is a ways off. David]

  3. 3

    Clear and cogent–thanks!

    (I will say, though, that the discussion under the “runaway methane feedback” is much clearer if you take the time to consult the link provided–at least as far as the second point, anyway.)

    [Response:I guess the information you are getting from that link is the idea of the feedback which I guess I neglected to explain. Warming causes methane release, which as a greenhouse gas drives further warming, and on and on. David]

  4. 4
    Hank Roberts says:

    So possible controls for methane are

    – finding and fixing point sources — leaks in the methane/natural gas distribution pipelines, and capturing all the gas being flared off from oil wells worldwide.

    – addressing surface sources in discrete locations — wetlands, rice plantations, dammed up rivers with decaying material at the bottom (those combined with chlorine produce for carcinogens in the water supply I recall)

    – geoengineering the atmosphere based on claiming the problem
    to address is diffuse leakage from undersea where we can’t get at it.

    This makes sense of what’s been happening. Are there decent numbers on the various sources?

    I recall a variety of possible approaches to agriculture to reduce methane sources.

  5. 5
    Edward Greisch says:

    Thanks. I can stop worrying about methane hydrates.

  6. 6
    wili says:

    Thanks for posting on this.

    Two points for now:

    1) Wouldn’t any spike in ice core shorter than decadal period be smoothed due to gas migration so be difficult to detect?

    [Response:Yes, but they would be detectable in the higher-resolution Greenland cores, see some of the comments in Revkin's piece , e.g. by Valérie Masson-Delmottehere.]

    2) Aren’t there large pools of free methane beneath the cap of methane hydrate? If these caps start dissolving, couldn’t that prompt a rather sudden large emission of methane?

    [Response:Richard Alley addresses this in the Revkin blog link also. David]

    (I hope we can have this conversation free of snide comments from certain posters.)

  7. 7
    Anonymous Coward says:

    Geoff (#2),
    -the satellite pictures you’ve linked to have a small range and highlight regional variations from one year to the next (in other words they don’t show large changes or a trend)
    -the amounts of methane observed by Semiletov according to newspaper articles were small on a global scale (David pointed this out in general terms)
    -yes, important feedbacks are poorly understood (and some may perhaps be unknown) but that’s not an excuse for baseless speculation
    -no, policy makers are not lulled in a false sense of security (the IPCC reports are alarming enough), for the most part they simply have other priorities than the future of our planet (such as various power struggles)

  8. 8
    Ray Ladbury says:

    We will look back on this as the Great Polar Fart of 2012.

    Sorry. It had to be said.

  9. 9
    DP says:

    This explains why there was no catastrophic release in the Eemian, when Summer temperatures in the Arctic were 4C warmer than now.

  10. 10
    bilimdili says:

    Good work.

  11. 11
    Solar Jim says:

    On the other hand (a fictional projection):

    Despite the abundance of inaccurate but reassuringly conservative projections of how a multifaceted planetary response should now be unfolding due to radiative forcing from carbonic acid gas, and given certain constraining assumptions about projections, we shall soon find out how nation-states interact with the melting Arctic when floating atomic fission reactors are sent by Russia to power petroleum extraction platforms in an ice-free summer sea.

    Hope a hot one doesn’t sink and discredit our calculated assumptions about the stability of hydrates. I’m sure this won’t happen, since it isn’t science (just the usual insanity).

    [Response:Assumptions about heat flow probably matter more than the stability of hydrate per se. David]

  12. 12
    DougO says:

    I have always wondered if rising sea levels would increase hydrostatic pressure on the sub-sea methane deposits, thus tending to increase thier stability, and acting to off-set the slowly increasing ocean temperature. Anyone know if those two forces are likely to cancel each other out, or is one more likely to overwhelm the other?

  13. 13

    #3 inline-”[Response:I guess the information you are getting from that link is the idea of the feedback which I guess I neglected to explain. Warming causes methane release, which as a greenhouse gas drives further warming, and on and on. David]”

    No, I was OK with feedbacks in general. It was helpful in differentiating ‘methane runaway feedback’ specifically; I wasn’t quite sure how that was unlike other compound terms involving the word ‘runaway’–if that makes sense.

  14. 14

    #8–”It had to be said.” Opinions may differ on that. . .

  15. 15
    WhiteBeard says:

    # 9, DP, 4 Jan 2012, 3:45 PM,

    ’xactly.

  16. 16
    Dennis Denuto says:

    Doug O: Given the shape of the hydrate stability curve, temperature is far far more important than pressure in deep marine settings.

    It is good to see a detangling of these issues, where all arctic methane was commonly ascribed to hydrates instead of the other large sources, that any and all releases were assumed to be new and not just newly-found, were all were assumed to be related to recent warming and not the much larger transgression, and the distinction between deep marine (Svalbard) and relict permafrost (ESAS) was seldom made. Thanks David.

    Question, if you take an exposed shelf with permafrost and hydrates and hit it with a 15F temp change at the seafloor via transgression for 10000 years…how is it even possible that another couple degrees change in air temp could have any discernable effect?

    [Response:Transgression, for the non-geological reader is flooding by rising sea level. There's permafrost, meaning soil/sediment colder than the freezing point of water, on the Siberian shelf because the air was so cold when the shelf was exposed during the last ice age. Very complicated playing field, but you're right, a bit of water warming is probably a small perturbation to the huge temperature change when it flooded, from which the permafrost is still responding. There's also frozen hydrate beneath the sea floor, because the hydrate freezing temperature is somewhat higher than the pure ice freezing point, so it doesn't rely on that extreme transgression thing to drive it. Good question. David]

  17. 17
    John says:

    DougO @ 12

    Between ocean tidal changes and low/high pressure system (extreme lows being hurricanes), one can surmise that a few inches of increased sea level rise would be indiscernible. If you believe that the max/min ocean floor column pressure is already near a critical point, then sure, a slight change in seal level could tip the scale.

    Here is another way of looking at it – 33′ of water column = 1 atm (14.7 psig) at say 3,000 ft, the pressure is 1,336 psi. A change of a few inches or even a few feet in seal level are not terribly significant.

  18. 18
    Dave Rado says:

    You don’t mention methane from cows (which periodically gets a lot of scare story coverage). Is that totally insignificant?

    [Response: No. Anthropogenic sources of methane have more than doubled atmospheric concentrations, and contribute about 0.5 W/m2 to the anthropogenic radiative forcing. There are multiple sources for this - farm animals among them (also oil and gas operations, leakage, landfills, and irrigation). David is focusing on methane feedbacks, not direct forcings. - gavin]

    And why does it count it as a duplicate post when the recaptcha rejects one’s post and one tries again?

    [Response: A question for the ages. Actually, if you fail recaptcha the comment is stored as 'spam' in the database and can be fished out if needed. So submitting the same comment is a duplicate - which is flagged. - gavin]

  19. 19
    John E. Pearson says:

    2 Geoff wrote: “Did Natalia Shakhova and Igor Semiletov really see much bigger plumes of methane this year than two years ago? If they did would be strange that 10000 year old warming should now be causing it.”

    In their 2010 science paper http://www.sciencemag.org/content/327/5970/1246.full.pdf they write: “To test our hypothesis, we have undertaken annual field campaigns (August to September, 2003 to 2008; six cruises in total), one helicopter survey (September 2006), and one over-ice winter expedition (April 2007) (20, 21).”

    I have not read the full article carefully but its hard to imagine how they could have characterized the variability (of the methane flux) with the 8 of trips they’ve taken.

  20. 20
    Hank Roberts says:

    Thank you Japan!

    GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L15807, 6 PP., 2011
    doi:10.1029/2011GL047871
    http://www.agu.org/pubs/crossref/2011/2011GL047871.shtml
    Methane observations from the Greenhouse Gases Observing SATellite: Comparison to ground-based TCCON data and model calculations

    Key Points
    CH4 is now successfully being retrieved from GOSAT satellite
    Validation against ground-based data shows good agreement
    Excellent agreement to model simulations as a first step …

  21. 21

    Thank you, thank you, thank you.

  22. 22
    Russell says:

    At the other end of the geological time spectrum lies shungite, a sort of amorphous glassy carbon f forming layers thick as coal seams in the very old metamorphic rocks of Karelia and the Baltic shield.

    It contains no visible microfossils, leading some to postulate that it originated as a thick marine algal mat.

    Anyone know how it fits with currrent theories of bacterial methane metabolism ?

  23. 23
    Rob Painting says:

    “Methane is also one of the usual suspects for the PETM, which consisted of about 100,000 years of isotopically light carbon, which is thought to be due to release of some biologically-produced carbon source, similar to the way that fossil fuel CO2 is lightening the carbon isotopes of the atmosphere today, in concert with really warm temperatures. I personally believe that the combination of the carbon isotopes and the paleotemperatures pretty much rules out methane as the original carbon source”

    Don’t you then run up against some serious mass balance problems if the culprit was organic carbon?

    [Response:No, since the isotopic label of organic carbon (of around -25 o/oo) is about half that of biogenic methane (-60 o/oo), it would take about twice as much organic carbon to deliver the same isotopic spike as the methane would. And the paleotemperatures indicate that it would have taken a lot of carbon to warm things up that much, unless the climate sensitivity was extremely high. Mass balance works better if it came from organic carbon. David]

  24. 24
    Dennis Denuto says:

    sorry for the multiples… rats!! the captcha thing was fooling me…

  25. 25
    Thomas says:

    Thanks, I run into a lot of “lurid alarmism” to borrow Anon Coward’s phrase. Its good to have something to counter it with.

  26. 26
    wili says:

    So Richard Alley cited a Liu who wrote:

    “To increase the store of free gas beneath the clathrate layer, the pressure must rise to displace more water. But the pressure cannot rise too high before it will wedge open cracks through the clathrate and let gas out. Also, when the methane and water combine to make clathrate, they reject most of the salt in the water, making salty brines that are harder to freeze, until clathrate, salty water, and free gas can coexist, allowing the free gas to escape in some places by bubbling through the salty water”

    I don’t see how this proves that there cannot be large pools of free methane. It is one persons thought experiment that I find rather incoherent.

    Something is going on with methane over the Arctic Ocean. Perhaps it is not caused by global warming, but it will certainly contribute to it, and so it is worth taking seriously and trying to understand what is going on rather than trying to sweep it under the rug.

  27. 27
    Hank Roberts says:

    David, I note the turnover/replacement time for marine plankton nowadays is less than 2 weeks — which would suggest to me that the doubling time for marine plankton, and the DMS they’d produce, and the clouds _that_ would induce, might change very fast as a response to a sudden methane spike — a bloom, basically, but in response to a big input of methane. That input might be consumed within weeks of reaching the ocean, whether or not it even got into the atmosphere.

    This is pure speculation, but — any thoughts on how much faster the climate sensitivity feedback might be if that were the case? What would the next limiting factor likely be?

    [Response:That DMS - cloud link got people all excited when it was first proposed, the Gaians especially liked it, but I don't have the impression that it makes a huge difference in today's climate. One question is how clean the atmosphere would be particles if we didn't exist. DMS only has a large impact in air with no other cloud condensation nucleii. Might be wrong about that, not something I keep up with. But the clouds would have a cooling impact, a negative feedback, so I'm not sure I'm following the thread of your idea. David]

  28. 28
    Dennis Denuto says:

    One thing on the “methane bubble”: I think the lack of such things at an important scale is probably true, but it is not at all clear. The natural release mechanism linked to is not real obvious and there are a few large blow-outs on arctic shelves that folks like C. Paull have attributed to more or less catastrophic releases (the pingo-like features). But these may be more geohazard, drilling issues than they are climate issues.

    Anyway, I agree that hydrate methane is likely secondary to other methane even in the arctic, that arctic methane is a drop in the global methane bucket anyway, and that global methane is far secondary to Co2 in importance. So, my question is, do we see any real 1st order science issues remaining related to hydrates and climate? What we need is a way to fingerprint methane such that one can tell if or maybe even how much of it had passed through a hydrate filter?

  29. 29
    R. Gates says:

    I agree that CO2 is the prime greenhouse mover “in our lifetimes”, and of course, if the worst case scenario comes to pass, methane’s influence won’t really matter that much in the longer term Still, I would love to get a feel for how much CH4 and N20 will add to the temperature increase from a doubling of CO2. Suppose we take the best current average estimate per doubling of CO2 of about 3C. How much will the increasing methane and N20 add on top of this 3C?

    [Response:Well, today methane is about 25% of total anthropogenic radiative forcing, and other gases including N2O are another 25%, but it's hard to speculate about in a warmer climate. Methane is a transient gas as described above, but N2O has a lifetime of 150 years in the atmosphere, so it has more history dependence than methane has (not as much as CO2). David]

  30. 30

    More views by climate scientists on global warming and Arctic Methane, to add to this valuable discussion. Rates of CH4 release and short current atmospheric lifetimes do impose some constraints that can bound its climate feedback.

    http://dotearth.blogs.nytimes.com/2011/12/28/more-views-on-global-warmin-and-arctic-methane/

  31. 31
    Anonymous Coward says:

    R. Gates #28
    The main effect of CH4 in the long run is to increase the amount of CO2 (see David’s post). Rather than affecting the warming per doubling, it mainly affects the timeline of the doubling.
    What you perhaps wanted to ask is how much would CH4 increase the expected warming per teraton of fossil carbon released in the atmosphere. I would be interested in expert guesstimates on the matter as well. This is especially pertinent since Matthews, in a paper promoting this metric (discussed on RC in 2010), assumed that CH4 would be offset by aerosols(!).

  32. 32
    Rob Painting says:

    David Archer @ 23 – I understand the reasoning that the greater amount of organic carbon required, gets one closer to the inferred paleotemps, but it’s a long way short (to say the least). And in what form could the organic carbon possible have been? The suggestions thus far are on even shakier ground than the methane hydrate capacitor idea.

    Isn’t it more likely that the Earth’s climate was in fact more sensitive back then? Have you seen these papers?:

    Enhanced chemistry-climate feedbacks in past greenhouse worlds – Beerling (2011)

    Large methane releases lead to strong aerosol forcing and reduced cloudiness – Kurten (2011)

    The ridiculously large organic carbon releases required, to match the isotope excursion, surely relegates itself to the bottom of the pile on that basis alone.

    [Response:It could have been peat, or sedimentary organic carbon that suddenly degrades. The release time was ~10,000 years, they say, so time isn't a problem. It's certainly easier to imagine a smaller release of methane than a larger release of carbon from organics, but the proposed higher climate sensitivity of that time is hard to imagine too, given that it was a world with no ice albedo feedback. The situation forces us to believe at least one "impossible" thing before breakfast. Choose your poison, I guess. David]

  33. 33
    Geoff Beacon says:

    David

    Thanks for saying in reponse to me at #4

    I’m with you on models in general, they often underpredict observations (ice sheet models, for example), often because they miss feedback, and they surely should be trumped by data where it’s available.

    I wish you could point this out to policy makers. I stopped Chris Huhne, the UK Secretary of State for Energy and Climate Change last year: He thought the missing Arctic feedbacks were now in the climate models.

    I subsequently asked Kevin Schaefer of the NSIDC to send me a quote. He said:

    If I were given the opportunity to talk to Chris Huhne, I would say

    1. We must reduce total, global fossil fuel emissions.

    2. None of the IPCC AR5 projections include the permafrost carbon feedback.

    3. We must allocate 15% of total allowed global emissions to account for the permafrost carbon feedback.

    4. The Department of Energy and Climate Change should definitely look into the permafrost carbon feedback because it implies a 15% greater reduction in fossil fuel consumption.

    I understand Kevin was referring only to CO2 not methane – any methane would enhance this effect.

    I have found that statements such as yours above very difficult to extract and I don’t remember any climate scientist volunteering this opinion. Is that due to climate scientist solidarity? If so we have a problem of trust.

    Do you agree that “None of the IPCC AR5 projections include the permafrost carbon feedback.”?

    [Hope you're reading this Chris. Did you like my article in Challenge?]

    [Response:If I see any policymakers today I'll be sure to mention. Paleoclimate modeling generally finds that the model simulations of, say, abrupt climate changes are generally good, in the right direction, but muted compared to the reconstructed data. Richard Alley made this point in an AGU talk I heard him give, I don't think it's a secret. And ice sheet models are widely recognized to be limited in their responses, the whole field is working feverishly to make them better. The permafrost feedback is a carbon source, and generally the model are run with some prescribed atmospheric CO2 trajectory, sort of subsuming that and any other carbon cycle feedbacks. It would amplify the fossil fuel CO2 forcing. On the other hand, the land biosphere today is taking carbon out of the atmosphere. So it's hard to model, exactly, makes more sense for now to sort of include that possibility in the forcing. It's speculative. David]

  34. 34
    John Mason says:

    Interesting post – thanks, David. Like many I have been looking into this issue recently. However, it seems to me that with respect to the East Siberian Arctic Shelf we are talking about a relatively data-poor area (until recently, very data-poor). That makes the reports from the area relatively difficult to interpret, despite the obvious problems with finding a mechanism for a large abrupt methane release and the lack of evidence in ice-cores for same to have occurred in any of the geologically recent deglaciations.

    Cheers – John

  35. 35

    On the point that methane decays to CO2: in the long run I can see that as being the case, but could a very large methane event rapidly speed up other feedbacks like ice loss? That may be hard to discern in the resolution of the geological record, but could make a very big difference to the biosphere.

    [Response:Sure, fast-responding things like sea ice would probably respond within the decadal time scale of a methane spike. David]

    I took the trouble to read Raypierre’s Principles of Planetary Climate and that cleared up one big mystery for me: why methane is supposed to be a much stronger greenhouse gas than CO2: there’s so much less of it that the stronger absorbing parts of the spectrum aren’t yet saturated. I explain some of this on my blog, though Raypierre’s book is really the place to go if you want it explained properly.

  36. 36
    Mike Roddy says:

    “It’s the CO2, friend” is essentially a semantic argument. Those of us who are, yes, alarmed by the Semiletov/Shakhova evidence are quite aware that methane degrades into CO2, adding substantial amounts of carbon dioxide to our atmospheric thermal blanket.

    What Archer’s post did not address is the recent 1km wide methane plumes that have been observed in the Arctic, or the enormous measured increase of methane concentrations in Arctic water and atmosphere. These plumes, along with Walter’s work, indicate unusual and rapid releases.

    The data you cited assumes that a modest increase in methane/CO2 will still be less than our annual 7Gt and up AGW CO2 emissions. Even if this is true, accelerated methane releases in response to Arctic warming could be the early stages of a process that carries its own feedback loops.

    Finally, scientists, including on this blog, appear to be awaiting catastrophic bursts prior to validating the danger. Humans instead need to act cautiously and preemptively in light of recent events in the Arctic. Otherwise, black swans could kill us all, partly because scientists were afraid to be wrong, or called the new “liberal”, (horrors!), “alarmist”.

    It’s a little complicated to address the methane releases in the context of things like burning coal and gas and destroying forests. This is what scientists have to do, and forcefully. Gavin gets this, but some of the other contributors here err on the side of caution. Journalists are on the sidelines, and politicians are bought.

  37. 37
    Anna says:

    James Hansen published a paper a few years ago on methane which I found very illuminating. If I remember correctly, he essentially said that yes, the CO2 is the problem, but because methane has a much higher short term impact, you get more bang for your buck reducing methane emissions than CO2 emissions.

    He noted that it will take a long time for us to switch from CO2 intensive sources of energy to less/minimally intensive sources, but that reducing emissions of trace gases like methane might be easier and quicker.

    Ah, found the paper, it’s called “Climate change and trace gases” from 2007.

  38. 38
    Mike Roddy says:

    The notion that “journalists” have been scaring people with stories about methane is kind of absurd. Very few Americans have heard anything about methane in the media, as mainstream outlets have ignored it. Climate blogs only address a very small sliver of our society, as the rest of us belch merrily along.

  39. 39
    Geoff Beacon says:

    David

    Thanks to your reply (#32).

    You say

    The permafrost feedback is a carbon source, and generally the model are run with some prescribed atmospheric CO2 trajectory, sort of subsuming that and any other carbon cycle feedbacks. It would amplify the fossil fuel CO2 forcing.

    Do you expect these feedbacks lag behind the forcing. If so, is there much in the pipeline?

    [Response:Sure the feedbacks lag. Even the warming lags the forcing, then it takes decades, even centuries to melt permafrost etc. David]

    To make rational policy decisions don’t we have to speculate and make a best guess?

  40. 40
    John E. Pearson says:

    David wrote: “The only way back to a natural climate in anything like our lifetimes would be to anthropogenically extract CO2 from the atmosphere.”

    I’d love to see an RC thread on this.

    [Response:Good idea, watch this space. David]

  41. 41
    Greg Robie says:

    The title chosen is an interesting inference. It is one whose import—and technical accuracy—is lost on all but the most fluent in the specificity of the language of science. The blue collar worker in me senses something is off with this choice relative to our condition. Is there is a bit of professional jealousy functioning as a muse for this Shakespearian allusion? With methane appearing to get the attention which (as is rightly noted) CO2 should be getting, such a feeling would be ‘reasonable’—if not fully reasoned.

    Drawing on my knowledge gained in blue collar work regarding insulation, a political message is sacrificed to “theological” purity with the title equating the observed exponential increase in East Siberian continental shelf methane out gassing with “nothing” relative to CO2′s importance. Is the exponential nature of the impact insulation has relative to heat transfer via conduction not being modeled accurately for the Arctic? While greenhouse gases are primarily considered relative to their radiant heat transfer dynamics, does the consequenced increased Arctic cloud cover and types represent a poorly understood (and modeled) conduction force? Also, don’t these two forces invoke the third factor in heat transfer, that of convection, which may also be different in the Arctic than what is understood for the tropics?

    Consider: the relative density of cold air, in conjunction with the Coriolis Effect affects the troposphere at the poles. It is less thick. What if that difference functions—if only simplistically—as a multiplier in terms of modeling factors? If such was proportional, and an enhancing factor, what is perceived as happening in small ways might need to be increased by 140% to have meaningful parity with what is currently thought to be of greater importance and the tropics. In addition, any bets that the impact might only be proportional, if such is the case. Career biasses can blind.

    In relative terms, there is a lot that is known about the tropics and how it drives the climate. Is this because the poles are a bit less comfortable to hang out at and gather data from? Between the Coriolis Effect and the tilt of the earth’s axis, a lot forces can be observed and modeled to be center in the equatorial zone in terms of such being primary factors. However, to what degree might such also be a consequence of observer bias? Is climate change in the Ferrel Cell “the sound of one hand clapping” or integral to a less well understood Polar Cell with unique dynamics? Last winter (northern hemisphere), didn’t the polar jet move so as to all but subsume the Ferrel Cell for the Eastern US and Europe? What multiplier is necessary for that observation to be modeled relative to the dynamics of the climate—as assumed—in the Polar Cell? Would 140% cover it?

    Anyway, there should be much ado about CO2, and politically, in the United States, there isn’t (except for a due diligence to pursue the BAU track and ‘recover’ a collapsed economic paradigm; i.e. rally around trusted delusional thinking). The technical definition of abrupt climate change, in some ways, justifies this reminder that it is CO2, not CH4, that is capitalism changing the climate (stuck accelerator & broken breaks metaphor in “Its All About Me(thane)” post a couple of years ago)—though I still think my rocket with liquid fuel first stage engines and solid fuel second stage ones whose ignition is tripped by an uncalibrated altitude switch, is a better one.

    In terms of policy making here in the US (& to the degree rationality currently informs public policy), tipping points, which are the “altitude switch” at which the fuse of the methane time bomb is lit, are of public interest and policy concern. Don’t observations in the face of know uncertainty (and know unknowns—unknown unknowns withstanding)—make the concept of tipping points that which needs a language, both in popular and scientific rhetoric . . . and is something this essay has missed an opportunity to engage in?

  42. 42
    Dennis Denuto says:

    I note this was the summary of Keith Kvenvolden’s 1988 summary paper in Glob Bio Cycles…

    SUMMARY
    Present evidences suggest that global warming is under way, with its effects already noticeable in the Arctic. This warming likely results, in part, from the greenhouse effect, due to the ever increasing amounts of atmospheric carbon dioxide. The amount of atmospheric methane is increasing more rapidly than that of carbon dioxide, but the current greenhouse effect of methane is almost an order of magnitude less than that of carbon dioxide. Global warming will eventually penetrate the surface of the Earth and in the process destabilize gas hydrates. This destabilization will likely occur first and most intensely in the very shallow, nearshore regions of the Arctic Ocean where offshore permafrost exists. The processes of offshore permafrost warming and methane release may already be in progress, but the amount of methane presently being released and to be released during global warming in the 21st century is probably not particularly large and will contribute minimal positive feedback to the global-warming phenomenon.

  43. 43
    Lynn Vincentnathan says:

    A denialist blogger wrote this; is there anything to it, does he mean that released CH4 from hydrates would have no warming effect at all:

    Since methane hydrate decomposition is an endothermic reaction [ absorbing heat ] it is self-quenching. This should have been a question that was asked and answered when it was first proposed. It’s a testament to the lack of scientific knowledge that the AGW’ ers bring to the discussion.

    [Response: Complete nonsense. The role of methane being discussed here is as a greenhouse gas, nothing to do with the heat generated or used in chemical reactions. It is in fact a testament to the lack of scientific knowledge that the skeptics bring to the discussion. - gavin]

    [Response:I presumed the person was arguing that the heat absorbed in the dehydration would be a negative feedback to that process, thereby preventing or slowing down CH4 release. The second sentence is the giveaway that an agenda drives the argument.--Jim]

    [Response:It is true however that the rate of hydrate "decomposition" (melting) is limited by how quickly heat can diffuse down there. So it takes time for hydrates to melt just like it takes time for peat to decompose. Perhaps that was what was meant. In which case it would be like the old trick of "revealing" the band band saturation effect of greenhouse gases as though this wasn't already in the textbook on the subject. David]

  44. 44
    Icarus says:

    Interesting and informative article, thanks. Is the rate of warming significant in this discussion? I’ve read that we are warming up the global climate at least ten times faster than the fastest known events of the past (e.g. the PETM). If there are no analogues in the palaeoclimate record for today’s rapid warming event, then perhaps that would make it difficult to predict future climate trajectories from the palaeoclimate evidence. Are the outcomes dependent upon the rate of warming, or do we just get to the same place but sooner?

    [Response:There is an effect which they call the "efficacy" of ocean heat uptake. As the oceans absorb heat (the transient) that process somehow scrambles the atmosphere to vent a bit heat as well to space, something like that. For ocean acidification, a faster transition like ours has less time to be buffered by the CaCO3 cycle in the ocean (time scale between 1-10 kyr) and so the pH spike will be much more intense than if it took 10,000 years like the PETM. As far as the methane cycle is concerned, if methane release is able to respond quickly, the resulting elevated methane concentration would go up as the time scale got quicker. Lots of time dependence. David]

  45. 45
    Hank Roberts says:

    > to anthropogenically extract CO2 from the atmosphere.

    One method is already underway — increased consumption by, and reproduction of, bacteria and algae in the ocean. Search for:

    jackson “rise of slime”

    for much about that. It’s already underway.

    It’s not an -intentional- choice and it’s not a -human-friendly- route.

    We’ve kicked off this process far faster than nature would have.

    “… In many places — the atolls of the Pacific, the shrimp beds of the Eastern Seaboard, the fiords of Norway — some of the most advanced forms of ocean life are struggling to survive while the most primitive are thriving and spreading. Fish, corals and marine mammals are dying while algae, bacteria and jellyfish are growing unchecked. Where this pattern is most pronounced, scientists evoke a scenario of evolution running in reverse, returning to the primeval seas of hundreds of millions of years ago.

    Jeremy B.C. Jackson, a marine ecologist and paleontologist at the Scripps Institution of Oceanography in La Jolla, says we are witnessing “the rise of slime.” …” http://articles.latimes.com/2006/jul/30/local/me-ocean30

  46. 46
    John E. Pearson says:

    45 Hank on rise of slime:

    This is not anthropogenic extraction.

  47. 47
    wili says:

    Some facts (please correct me if I get anything wrong):

    –methane has a GW potential of 105x CO2 on a decadal basis (Shindell et al. 2006)

    –seabed methane (hydrates and free methane) in the ESAS alone are estimated in the 1000Gt range.

    –Semiletov and a team of other experts were rushed up to the Arctic to investigate a ‘dramatic’ increase in methane release, described by some as “the sea bubbling as if it were boiling.”

    –Semiletov saw methane plumes an order of magnitude wider than any he had seen before in his many trips to the region.

    –the Barrow station recorded sharp spikes in methane levels in November

    –other sources show unusual increases in methane concentration over the Arctic this November over last November: ftp://asl.umbc.edu/pub/yurganov/methane/MAPS/NH/ especially

    ARCTpolar2010.11._AIRS_CH4_400.jpg and ARCTpolar2011.11._AIRS_CH4_400.jpg

    –a potential feedback has been proposed that once emissions of seabed methane start to increase significantly, they will create conditions (through warming, sea ice melt, disruption of sea bed…) that will essentially guarantee that all of the seabed methane will be released.

    –many models have represented seabed methane as including clathrate caps over pools of free methane

    These are among the reasons that some of us have expressed concerns about the recent reports of increased methane emissions.

    The main counterpoint presented here seems to be that the methane will likely not be released quickly enough to have a global warming potential of much greater than CO2.

    How certainly do we know this? Even if there is little good evidence of sudden release in the paleo-record, we are now increasing GHG concentrations in the atmosphere faster than at any time in the history of the earth, iirc. This is a new experiment we are conducting, and the exact degree to which and speed at which things will unravel cannot be known with certainty.

    The other point that is constantly made is that right now emissions from this source are ‘small potatoes’ compared to other sources. Of course. But if we are seeing the beginning of an exponential increase in this source, it won’t take long for it to be a very major contributor indeed.

    Of course, the main thing all this should tell us is that we need to decrease our GHG emissions–CO2 and CH4 and the others–to below zero very quickly indeed. Unfortunately, we seem to be doing the opposite–the global civilization seems to have something of a death wish.

    I do appreciate the discussion of this important topic here. I would also point out that Shakhova did not say that the recent increase in emissions were the result of GW, and she specifically emphasized that they had not made this claim. So we can hope that whatever the cause of the recent increase in emissions this summer and fall is self limiting or cyclical in some way, rather than the beginning of an exponential increase.

  48. 48

    Further to wili’s comment #47:

    We have a no-analogue scenario right now, especially in the Arctic.

    Mean global temperatures have risen more sharply (faster) than at any time in the record, have they not? The Arctic is warming twice as fast as the rest of the planet, but I dare say that is a real understatement, since temps are 20 degrees C above average. See: http://www.esrl.noaa.gov/psd/map/images/fnl/sfctmpmer_01a_30frames.fnl.anim.html

    Even if that is not correct, we have a situation where the ESAS is getting hit by (a) retreating sea ice causing a near albedo flip in the Arctic, heating up the sea exactly in the area in question (open water there right now), (b) increasingly warm oceans waters flowing in from both the Pacific and the Atlantic, (c ) rapidly rising sea-surface temperatures, and (d) increasing positive feedback from anthropogenic aerosols hanging over the Arctic Sea from pollution arriving from Asia.

    Also, further to wili’s posting of the AIRS CH4 for the Arctic for 2010 and 2011, I have added 2002, for comparison — you can see all three of these together at this link: http://climatechangepsychology.blogspot.com/2012/01/arctic-methane-local-pm-ascending-airs.html

    I do not believe that the answer lies in the up-to-now published literature. And I think it foolhardy to assume it does.

  49. 49

    #43–Just guessing, but I took it the same way Jim did.

    It seems a poorly-thought-out meme, even by the usual standards.

    Setting aside the vast over-simplification involved, I’d think that if asked whether a given endo- or exo-thermic reaction would become more likely under warming, you would pick the endothermic: The warmer temps supply more energy, and energy to drive the reaction is the postulated limiting factor.

    But then I’ve seen “IR absorption” re-characterized to be the functional equivalent of reflection (in order to argue against albedo feedbacks) so this shouldn’t surprise. Just more of the same ‘sciency’ stuff.

  50. 50
    Ron Manley says:

    Whilst methane is a powerful GHG it occupies a narrow, partially saturated spectrum which it shares with Nitrous Oxide (see http://www.climatedata.info/Forcing/Emissions/introduction.html) and the figure based on Kiehl and Trenberth). Not only is its spectrum narrower than for CO2 it is in part of the IR wavelength where the potential forcing effect is more limited than for CO2. This also seems to suggest that the impact of large increase in methane emissions would be limited.


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