RealClimate logo


Arctic Methane on the Move?

Filed under: — david @ 6 March 2010 - (Italian)

Methane is like the radical wing of the carbon cycle, in today’s atmosphere a stronger greenhouse gas per molecule than CO2, and an atmospheric concentration that can change more quickly than CO2 can. There has been a lot of press coverage of a new paper in Science this week called “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf”, which comes on the heels of a handful of interrelated methane papers in the last year or so. Is now the time to get frightened?


No. CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 60 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 90 miles per hour instead of 60. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it’s not the big story, nor does it look to be a game changer to the big story, which is CO2.

[Note: Edited Toyota velocities to reflect relative radiative forcings of anthropogenic CO2 and methane. David]

For some background on methane hydrates we can refer you here. This weeks’ Science paper is by Shakhova et al, a follow on to a 2005 GRL paper. The observation in 2005 was elevated concentrations of methane in ocean waters on the Siberian shelf, presumably driven by outgassing from the sediments and driving excess methane to the atmosphere. The new paper adds observations of methane spikes in the air over the water, confirming the methane’s escape from the water column, instead of it being oxidized to CO2 in the water, for example. The new data enable the methane flux from this region to the atmosphere to be quantified, and they find that this region rivals the methane flux from the whole rest of the ocean.

What’s missing from these studies themselves is evidence that the Siberian shelf degassing is new, a climate feedback, rather than simply nature-as-usual, driven by the retreat of submerged permafrost left over from the last ice age. However, other recent papers speak to this question.

Westbrook et al 2009, published stunning sonar images of bubble plumes rising from sediments off Spitzbergen, Norway. The bubbles are rising from a line on the sea floor that corresponds to the boundary of methane hydrate stability, a boundary that would retreat in a warming water column. A modeling study by Reagan and Moridis 2009 supports the idea that the observed bubbles could be in response to observed warming of the water column driven by anthropogenic warming.

Another recent paper, from Dlugokencky et al. 2009, describes an uptick in the methane concentration in the air in 2007, and tries to figure out where it’s coming from. The atmospheric methane concentration rose from the preanthropogenic until about the year 1993, at which point it rather abruptly plateaued. Methane is a transient gas in the atmosphere, so it ought to plateau if the emission flux is steady, but the shape of the concentration curve suggested some sudden decrease in the emission rate, stemming from the collapse of economic activity in the former Soviet bloc, or by drying of wetlands, or any of several other proposed and unresolved explanations. (Maybe the legislature in South Dakota should pass a law that methane is driven by astrology!) A previous uptick in the methane concentration in 1998 could be explained in terms of the effect of El Niño on wetlands, but the uptick in 2007 is not so simple to explain. The concentration held steady in 2008, meaning at least that interannual variability is important in the methane cycle, and making it hard to say if the long-term average emission rate is rising in a way that would be consistent with a new carbon feedback.

Anyway, so far it is at most a very small feedback. The Siberian Margin might rival the whole rest of the world ocean as a methane source, but the ocean source overall is much smaller than the land source. Most of the methane in the atmosphere comes from wetlands, natural and artificial associated with rice agriculture. The ocean is small potatoes, and there is enough uncertainty in the methane budget to accommodate adjustments in the sources without too much overturning of apple carts.

Could this be the first modest sprout of what will grow into a huge carbon feedback in the future? It is possible, but two things should be kept in mind. One is that there’s no reason to fixate on methane in particular. Methane is a transient gas in the atmosphere, while CO2 essentially accumulates in the atmosphere / ocean carbon cycle, so in the end the climate forcing from the accumulating CO2 that methane oxidizes into may be as important as the transient concentration of methane itself. The other thing to remember is that there’s no reason to fixate on methane hydrates in particular, as opposed to the carbon stored in peats in Arctic permafrosts for example. Peats take time to degrade but hydrate also takes time to melt, limited by heat transport. They don’t generally explode instantaneously.

For methane to be a game-changer in the future of Earth’s climate, it would have to degas to the atmosphere catastrophically, on a time scale that is faster than the decadal lifetime of methane in the air. So far no one has seen or proposed a mechanism to make that happen.


References

Dlugokencky et al., Observational constraints on recent increases in the atmospheric CH4 burden. GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L18803, doi:10.1029/2009GL039780, 2009

Reagan, M. and G. Moridis, Large-scale simulation of methane hydrate dissociation along the West Spitsbergen Margin, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L23612, doi:10.1029/2009GL041332, 2009

Shakhova et al., Extensive Methane Venting to the Atmosphere from Sediments of the East Siberian Arctic Shelf, Science 237: 1246-1250, 2010

Shakhova et al., The distribution of methane on the Siberian Arctic shelves: Implications for the marine methane cycle, GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L09601, doi:10.1029/2005GL022751, 2005

Westbrook, G., et al, Escape of methane gas from the seabed along the West Spitsbergen continental margin, GEOPHYSICAL RESEARCH LETTERS, VOL. 36, L15608, doi:10.1029/2009GL039191, 2009

234 Responses to “Arctic Methane on the Move?”

  1. 201
    Brian Dodge says:

    I was thinking about the mechanisms that remove CH4 from the atmosphere, and the recent decline in stratospheric water vapor noted by Solomon et al, and it occurred to me that increased GCRs might increase conversion of water vapor to hydroxyl radicals, removing water and methane from the stratosphere. I downloaded some CH4 data from CDIAC and some CR data from Oulu, and plugged it into my trusty(buggy and crash prone) Appleworks spreadsheet. The data only covers 8/93 to 3/2009. I normalized the data by the monthly averages for the first 12 years to remove annual cyclic variation, and got some interesting results. The flat portion of the methane concentration corresponds to low, not high CR levels, and there appears to be a threshold effect. It’s probably spurious correlation. Solar UV varies inversely with CR, and photodissociation may well dominate, which could explain the flat CH4 when the CR was low/UV was high. I haven’t found an easily accessible monthly solar UV dataset to plug into my spreadsheet yet.
    Graphs are at http://www.imagenerd.com/uploads/gcrvsch4-TfMuw.jpg – Pretty weird, eh? Any thoughts?

    [Response: There are definitely feedbacks associated with the hydrogen that methane carries. It’s a greenhouse gas, for one. I don’t remember what the balance of water vapor in the stratosphere is, between atmospheric mixing, cloud convection overshoot, and methane, but it’s definitely an issue. Just for fun: Lovelock calls methane little “hydrogen balloons”, carrying out the Gaian task of carrying methane to the stratosphere, letting the hydrogen escape to space, building up oxidation of the Earth. David]

  2. 202
    prokaryote says:

    A radical mechanism for methane buildup.
    Two scientists suggest a link between the atmospheric buildup of methane–an important greenhouse gas–and a shortage of a highly reactive molecule called the hydroxyl radical hydroxyl radical: see hydroxide. . Their surprising finding indicates that hydroxyl hydroxyl /hy·drox·yl/ (hi-drok´sil) the univalent radical OH.
    hy·drox·yl
    n.
    The univalent radical or group OH, a characteristic component of bases, certain acids, phenols, alcohols, carboxylic depletion in the Northern Hemisphere is about twice as severe as previously believed.
    http://www.thefreelibrary.com/A+radical+mechanism+for+methane+buildup-a010426291

    The major removal mechanism of methane from the atmosphere involves radical chemistryRadical (chemistry)In chemistry, radicals are atoms, molecules, or ions with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions…; it reacts with the hydroxyl radicalHydroxyl.
    The hydroxyl radical, OH·, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry…(·OH), initially formed from water vapor broken down by oxygen atoms that come from the cleavage of Ozone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O2.
    Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals…by ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV…radiation:This reaction in the troposphere. The troposphere is the lowest portion of Earth’s atmosphere. It contains approximately 75 percent of the atmosphere’s mass and 99 percent of its water vapor and aerosols….gives a methane lifetime of 9.6 years.
    Two more minor sinks are soil sinks (160 year lifetime) and stratospheric loss by reaction with ·OH, ·Cl and ·O1D in the stratosphere (120 year lifetime), giving a net lifetime of 8.4 years. Oxidation of methane is the main source of water vapor in the upper stratosphere (beginning at pressure levels around 10 kPaKPAKPA may refer to:* Kenya Ports Authority* Kilopascal , a unit of pressure* Known-plaintext attack, a method of cryptanalysis* Korean People’s Army* The Kosovo Property Agency* Also refers to the Montagnard name meaning “straight”….).The methyl radical formed in the above reaction will, during normal daytime conditions in the troposphere, usually react with another hydroxyl radical to form formaldehydeFormaldehydeFormaldehyde is a chemical compound with the formula CH2O. It is the simplest aldehyde. Formaldehyde also exists as the cyclic trimer trioxane and the polymer paraformaldehyde. It exists in water as the hydrate H2C2. Aqueous solutions of formaldehyde are referred…. Note that this is not strictly oxidative pyrolysisPyrolysisPyrolysis is the chemical decomposition of condensed organic substances by heating. The word is coined from the Greek-derived elements pyro “fire” and lysys “decomposition”….as described previously. Formaldehyde can react again with a hydroxyl radical to form carbon dioxideCarbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth’s atmosphere in this state…and more water vapor. Note that sidechains in these reactions may interact with nitrogenNitrogenNitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth’s atmosphere.Many industrially important…compounds that will likely produce ozoneOzoneOzone or trioxygen is a simple triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic O2. Ground-level ozone is an air pollutant with harmful effects on the respiratory systems of animals…, thus supplanting radicals required in the initial reaction.
    http://www.absoluteastronomy.com/topics/Atmospheric_methane

    However, much of the methane released from permafrost may remain in the atmosphere longer, due to OH depletion. The more methane there is to be oxidized, the more chance there is of OH depletion, and the longer it will take for methane to oxidize.
    http://knol.google.com/k/sam-carana/the-threat-of-methane-release-from/7y50rvz9924j/32#

    [Response: This is already taken into account in metrics like GWP, but is not as big an effect as you might think. We discussed this in Schmidt and Shindell (2003). – gavin]

  3. 203
    jcrabb says:

    In 2008 Shakovha wrote,

    The total value of ESS carbon pool is, thus, not less than 1,400 Gt of carbon. Since the area of geological disjunctives (fault zones, tectonically and seismically active areas) within the Siberian Arctic shelf composes not less than 1-2% of the total area and area of open taliks (area of melt through permafrost), acting as a pathway for methane escape within the Siberian Arctic shelf reaches up to 5-10% of the total area, we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause 12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming.

    http://www.cosis.net/abstracts/EGU2008/01526/EGU2008-A-01526.pdf

    Seems pressing, like being trapped in a Prius at 100mph.

    [Response: This is the most specific proposal for getting a lot of methane out that I’ve seen. If 50 Gton of methane did all come out within a few years it would have a radiative forcing of about 4 W/m2, according to MODTRAN for what that’s worth (single location, not counting the indirect effects of methane chemistry, old model, etc.) That’s big but so are volcanic eruptions, which can be -5 or so W/m2. The methane would oxidize to CO2 in about a decade, at which point 50 Gton C is certainly a lot of C, five years’ emission worth, but it’s not like a game changer exactly. David]

  4. 204
    Blair Dowden says:

    Thanks everyone for your help. I will do some more reading for a while, including spending some more time on this Raymond Pierrehumbert paper, which seems to be a very good summary of what is going on.

  5. 205
    Patrick 027 says:

    Re
    http://www.realclimate.org/index.php/archives/2010/03/arctic-methane-on-the-move/comment-page-3/#comment-165280

    Slow moving storms –

    It’s a bit more complicated than that, actually. On scales and for conditions where geostrophy is a good approximation, vertical wind shear tends to be proportional to a horizontal temperature gradient and inversely proportional to the coriolis parameter f (which is proportional to the sine of the latitude).

    A reduction in the temperature gradient makes the geostrophic wind more similar; but this could either involve a change in wind above or the opposite change in wind below.

    At some latidudes, in some seasons, in the zonal average, the meridional temperature gradient will decrease with global warming. However, in the upper troposphere, there is a general tendency for the pole-equator temperature gradient to increase.

    In growing baroclinic waves via counter-propogating mutually-amplifying Rossby waves (developing synoptic-scale low pressure systems, and highs too, though there is some assymetry), the wave pattern moves at some intermediate velocity between the upper and lower-level Rossby waves; thus, air blows through the systems from east to west in low levels and from west to east at upper levels, except when the systems are strong enough for the wave’s wind field to match and exceed the system-relative background-state wind; in that case the wind blows from east to west around a low only on the low’s cold side, … etc. This activity ultimately tends to horizontally-concentrate westerly (west-to-east) momentum at upper levels into a westerly jet but also transfer some westerly momentum down to the surface… (while it mixes heat downgradient horizontally and also transports heat upward). But there are variations in that pattern such as in NAM/SAM annular mode variations, and … a bunch of other stuff …

    (In the absence of such activity, considering a hemispheric steady-state Hadley cell*, westerly momentum would build up in the atmosphere acting on suruntil surface winds at high latitudes became westerly in spite of the equatorward motion – this would require some ageostrophic westerly wind component that would be driven by momentum transport from above… Of course, the extent of a Hadley cell, depending on how much mixing of momentum is allowed across streamlines in the meridional plane, is limited by conservation of angular momentum and also that the temperature at the poles can’t dip below absolute zero;… might be a bit more to it than that but anyway…)

  6. 206
    Patrick 027 says:

    “at some intermediate velocity between the upper and lower-level Rossby waves;”
    I meant the wind at those levels

    “This activity ultimately tends to horizontally-concentrate westerly (west-to-east) momentum at upper levels into a westerly jet but also transfer some westerly momentum down to the surface… (while it mixes heat downgradient horizontally and also transports heat upward). ”
    – Depending on intial conditions (if the storm track is displaced from the maximum in the westerlies, it may push the westerlies away ?)
    – Some of the effect on the temperature gradient may be counterintuitive (depending on what level of understanding your intuition is based on, of course). (PS based on the Ferrel cell (a consequence of this storm track activity), an initial guess might be that the storm activity produces an enhanced temperature gradient to it’s cold side at the surface; in that case, the storm track might migrate poleward; then lack of mixing equatorward of that would give rise to a second storm strack that would migrate poleward, taking the place of the first as it dies out. A nice simple scenario but I’m guessing incorrect even in a simplified world (?) (because inflow towards the belt of low pressure produced by storm track activity occurs after the lows become cold-core features at the surface (?)… the surface cold fronts meanwhile have gone equatorward, … well it gets complicated)…)

  7. 207
    prokaryote says:

    Why focus so much on the troposphere and stratosphere, when considerung methane uptake?

    An interesting feature is that the summer mesopause is cooler than the winter. This is sometimes referred to as the mesopause anomaly. It is due to a summer-to-winter circulation giving rise to upwelling at the summer pole and downwelling at the winter. Air rising will expand and cool resulting in a cold summer mesopause and conversely downwelling air results in compression and associated increase in temperature at the winter mesopause. It should be noted that in the mesosphere the summer-to-winter circulation is due to gravity wave dissipation, which deposits momentum against the mean east-west flow resulting in a small north-south circulation
    http://en.wikipedia.org/wiki/Mesopause

    Trends of mesospheric water vapor due to the increase of methane – A model study particularly considering high latitudes

    This Lyman-α flux values are used to determine the water vapor dissociation rate. The solar influence on the water vapor mixing ratio is insignificant at about 80 km within the NLC area but it becomes increasingly more important with growing altitudes. The rising water vapor concentration reduces the mesospheric ozone due to higher concentrations of the hydrogen radicals. This fact causes a positive feedback between both constituents above about 65 km. The dissociation of smaller amounts of ozone entails the production of less amounts of O(1D) destroying a smaller quantity of water vapor. The effect is most pronounced in the vicinity of the daytime secondary ozone maximum around an altitude of 85–90 km where the relative increase of the water vapor mixing ratio is strongest.
    http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V3S-4M6SG8R-2&_user=10&_coverDate=12%2F31%2F2006&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1245861860&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b772ea9d9b5fd7c478760357e39cc822

    Mesosphere-stratosphere transport during Southern Hemisphere autumn deduced from MIPAS observations
    http://cat.inist.fr/?aModele=afficheN&cpsidt=21376265

    Methanogenesis, Mesospheric Clouds, And Global Habitability
    http://geo.arc.nasa.gov/sgp/aero/aerocloud3.html

  8. 208
    wili says:

    The emphasis on the short half life of methane seems a bit disingenuous to me. The stat cited is that methane has 23 times the GW power of CO2. But that is over a century. So even if this stuff is released over the period of a century, each molecule will have 23 times the power of a CO2 molecule.

    And as jcrabb noted at #103 above, Shakhova puts the amount of carbon in these stores at 1,400 Gts.

    Since David presented this is a very potent threat in his book, either he was overstating his case then or is understating it here. I think when it comes down to it the emotional impact of knowing we are at the precipice is too much for all of us. There are many reasons that many people have been unable to accept the overwhelming evidence of AGW, but emotional is a basic one, as it now seems to be here.

    We are all denialists now.

    [Response: The global warming potentials you’re referring to are weighted according to time, with 100 years being one of the time horizons. But the lifetime of methane in the air is about a decade, no disingenuousness intended. David]

  9. 209
    Completely Fed Up says:

    “208
    wili says:
    12 March 2010 at 9:03 AM

    The emphasis on the short half life of methane seems a bit disingenuous to me. The stat cited is that methane has 23 times the GW power of CO2. But that is over a century. So even if this stuff is released over the period of a century, each molecule will have 23 times the power of a CO2 molecule.”

    Over that time.

    The numbers here are made up for illustration purposes and I don’t have a calculator to hand…

    1000 Methane Molecules. 100 times the power of CO2 but halves in volume every year.

    Year 1: 100,000
    Year 1 + 2: 100,000 + 50,000
    Year 1 + 2 + 3: 100,000 + 50,000 + 25,000

    Total effect: 200,000 units.

    1000 CO2 Molecules 1 times the power of CO2 but halves in volume every 200 years.

    Year 1-200: 200,000
    Year 1-400: 300,000

    Total effect: 400,000 units.

    Ergo, over 5 years, Methane is much greater than CO2. Over 500 years, CO2 is much greater than Methane.

  10. 210
    Completely Fed Up says:

    PS that isn’t how it’s done, but it shows the shape of the reasoning.

    [Response: It does indeed. David]

  11. 211
    Dan Olner says:

    Just read this via Slashdot: http://www.inhabitat.com/2010/03/11/china-developing-combustible-ice-as-new-energy-source/

    China: 90 years worth of energy from methane-ice, apparently. No idea what to believe. That story says it’s ‘better than letting it release through melting’ but would that be true? Burning it will produce co2 which is longer-lasting – and how much co2 would we be talking about from this project?

    [Response: A reporter asked me about this idea the other day, whether extracting it and burning it is better than letting it release directly. I guess there was a line in a many-authored paper I was on to this effect. But generally the methane that’s escaping to the air, if it’s from hydrate at all and not from decomposing peat, is disseminated through permafrosts and is not the same stuff that the oil company guys want to go after. So I told the guy I didn’t believe in methane extraction as a mitigation option against hydrate melting, that sounds like oil company bs to me. David]

  12. 212
    Hank Roberts says:

    The petroleum companies are hoping to go after stable deepsea hydrate formations in fairly pure forms, it looks like from a quick search
    http://scholar.google.com/scholar?q=mining+methane+hydrate+outcrop

    for example this: US DOE publication 2008
    Hydrate Production through CO2-CH4 Exchange
    Methane Hydrate Newsletter Fall 2008, (US Dep’t of Energy publication)
    By ConocoPhillips – University of Bergen Hydrates Team

    Scholar finds it here:
    http://rasmus.uib.no/People/nglbh/GANS/pdf/HMNewsFall08.pdf

    As David says, those are not currently our concern for atmospheric release.

  13. 213

    The first point obviously would be: is the methane going to be released anyway? “Extraction” seems like a problematic concept in this regard! If you must “extract” it, how imminent is the putative emission?

    OTOH, if emission is inevitable and there’s an option to burn, then logic says do it: you have CO2 with a greenhouse-intense “early life,” or you have CO2 without it. Clearly the latter is marginally better–especially if the energy produced displaced coal-fired energy from the mix.

  14. 214
    wili says:

    At #208, David kindly responded to my (doubtless hopelessly ignorant) inquiry about the relationship between methane lifespan in the atmostphere and its power as a GHG with the following:

    “The global warming potentials you are refering to are weighted according to time, with 100 years being one time horizons. But the lifetime of methane in air is about a decade….”

    So now I, as a non-expert, am confused. I assumed that the lifetime of methane in the atmosphere was a kind of belljar curve with a longish tail. That tail means that there is enough methane, even after a century, in the atmosphere for whatever quantity initially released to have about 23-25 times the gh potential of the same amount of CO2 (over the same time frame).

    But the same amount of methane,as I have understood it, would be largely still present in the atmosphere in say seven years after release, at which point it would represent well over 100 times the gh potential of CO2 over that same time frame.

    Is this just way off? (I’m afraid the Fedup illustration did not illuminate much for me–what, by that model is the warming potential of methane over the period of a century?)

    [Response: Looks like you have the basic idea right. Since CH4 decays at a much faster rate than CO2, it’s GWP relative to CO2 will decline as the reference time frame increases (because GWP is calculated for an equivalent amount of gas): from 72 over 20 years to 7.6 over 500 years. See the IPCC AR4 WG1 report, section 2.10 and Table 2.14.–Jim]

    I am doubtless missing something basic here. Sorry for my relative density ;-}

  15. 215
    Gilles says:

    “1000 Methane Molecules. 100 times the power of CO2 but halves in volume every year.
    ….
    Total effect: 200,000 units.

    1000 CO2 Molecules 1 times the power of CO2 but halves in volume every 200 years.

    Total effect: 400,000 units.
    PS that isn’t how it’s done, but it shows the shape of the reasoning.

    Yes it does but your numerical application is wrong. If methane had 100 times the warming power but the decay time is 200 times smaller (one year instead of 200), then it has indeed a 100/200 = 1/2 warming power integrated over its lifetime, what your calculation confirms. But if the right number is 25, with a life time 10 times smaller, it means that the instantaneous warming power is more 250 times , divided by 10 for the lifetime. Doesn’t change the fact that methane from arctic is only a few percent of a global 20 % of methane contribution to warming, of course.

  16. 216
    Marcus says:

    Wili: “I assumed that the lifetime of methane in the atmosphere was a kind of belljar curve with a longish tail. ” This is not true. Methane’s exponential decay means that there is very very little methane left after a century – effectively zero. (this is unlike CO2, which has a very complicated lifecycle, and therefore while given a pulse of emissions, the concentration of CO2 has a fast initial decay some percentage hangs around for thousands of years).

    The actual definition of the GWP is the total sum of radiative forcing over the century, not the amount of radiative forcing at the end of the century. So this is an area under the curve problem.

    If you go look at the AR4 WGI report that Jim mentioned, you’ll find that the instantaneous forcing of CH4 is 37 compared to 1.4 for CO2 – per ppb in the atmosphere. Correct for mass (44/16), and you get about 73. So a ton of methane has 72 times the effect after 1 second as a ton of CO2. Therefore, the “1 second GWP” is about 72. As time passes, the ratio of CO2 left to CH4 left increases, and so the relative radiative forcing of CH4 decreases… but since the GWP is the integral over time, you are adding together the time that CH4 was 72 times CO2 to the time that CH4 was 20 times CO2 to the time when CH4 was 0 times CO2 – so at 100 years, even though CH4 is about 0 times CO2, the initial period is still being added in.

    (note that there are some other corrections in the GWP unique to CH4 because its ozone and strat. water vapor effects are added in – I think it is a rough times 1.4 multiplier)

    -Marcus

  17. 217
    Ray Ladbury says:

    wili,
    First, a nit, since it is clear that you are trying very hard to understand, I’d call you “learning” rather than “ignorant”.

    Remember that because there is so much less CH4 in the atmosphere, and because CH4 is absorbing where H20 and CO2 are not, that it is taking a bite out of a virgin chunk of the IR spectrum.

    http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png

    So a large influx of CH4 causes a large imbalance and rapid warming. However, since the methane has a short lifetime, it has decayed to well under a quarter of its initial abundance before the planet has had time to reach equilibrium again. So, essentially when you look at the GWP, if I understand it you are looking at the area under the 100 year curve and dividing by 100 years. (More or less corrrect, Jim?)

  18. 218
    wili says:

    Thanks even more for all the responses. But now I’m a bit more confused on one point. Jim says the GW potential of methane over 20 years is 72 times CO2, but Marcus gives the same multiple for the GWP during the first second it is released. I can’t see how these could both be right, but perhaps I’m missing something basic?

    [Response: Don’t trust an ecologist to educate you on greenhouse gas forcings, but here’s my explanation. Marcus was talking about the instantaneous forcing ratio (CH4 to CO2) per unit weight, which incorporates radiative efficiency and molecular weight differences, and is thus about (370/14)*(44/16) = 73. But the GWPs are calculated over various intervals (20, 100, 500 years), and these incorporate the indirect effects of CH4 on O3 and stratospheric H2O radiative forcing, which are not included in the instantaneous calcs. Therefore the CH4 GWPs at the 3 time points are higher than would otherwise be. But I could be wrong.–Jim]

    The fact Jim pointed out that methane still has seven times the GHP of CO2 even after half a millennium again leads me to think that release of any significant portion of the 1,400 gigatons of the stuff over that time period may well be possible and dangerous.

    Still trying to make sense of the calming tone of the lead post given what looks to be very ominous data. Perhaps David or others could say how long they think it would take for a significant amount of methane hydrate (is the term ‘clathrate’ still used?) might be released–multiple millennia?

    Another thing, is there a point at which methane’s GWP dips below that of CO2, and what point would that be?

    Or, since it mostly decays into CO2, is the GWP of that produced CO2 figured in so it would never drop below the CO2 GWP number?

    Thanks again in advance for informative responses, and apologies again if I am missing the obvious.

  19. 219
    Geoff Beacon says:

    David’s response to 169 Milan, to the possibility that methane feedback was a cause of the PETM warming event was

    Or carbon release from peats, or soil carbon, or biomass, or the ocean somehow-like-it-did-during-the-glacial-cycles.
    Methane is not the only game in town.

    My notes from a long conversation with a leading climate modeler contain this

    PLAN B

    There should be a plan B for climate change if reducing emissions of CO2 cannot be effected soon enough. This would take more seriously the effects of pathways with shorter timescales than CO2, such as methane, ozone (NOx as a precursor), nitrous oxide and black carbon. Plan B should also consider geoengineering. Sulphate looks best but Salter’s boats have a regional effect that must be closely monitored.

    It may be necessary to accept ocean acidification caused by rising CO2 levels. It should be remembered that CO2 does have a fertilising effect on plant growth.

    Plan B is not a substitute for addressing CO2 but shorter term measures may become necessary.

    Air travel is not a large part of the climate problem. Livestock is a big issue.

    The climate feedbacks that David mentions increase the need for a plan B. I know of no policy makers aware of this issue.

    In the UK there is a standard, PAS2050, which specifies how products and activities should be assessed to measure their impact on climate change. But it’s measurement is aimed at a 100 year time-scale. It is of little use for Plan B. A PAS2050(Plan B) is required. But not much easily digestible literature on climate is available to help the climate change bean counters. The best so far is Unger et. al. “Attribution of climate forcing to economic sectors”
    (http://pubs.giss.nasa.gov/docs/notyet/inpress_Unger_etal.pdf).

    The limitation of this paper (for climate bean counting) is the aggregation of climate forcing agents into broad economic sectors. Finer detail is needed. We should now not just the impact of road transport over time but the difference between different types of road transport – diesiel, electric &etc.

    I am looking forward to some literature that can help, ideally with the a graph of the major climate forcing agents and their effects over at least a century to give the climate bean counters something to work on.

  20. 220
    Geoff Beacon says:

    There is a paper by Shindell et al., “Improved Attribution of Climate Forcing to Emissions“,
    http://www.sciencemag.org/cgi/content/abstract/326/5953/716

    This paper argues that methane is more potent than previously realised due to the interaction with black carbon. The paper gives a revised Global Warming Potential for methane measured over 100 years as 33. This is an increase of over 30% compared to the value of 21 given in the IPCC Second Assessment Report used for the Kyoto Protocol. Over 20 years. Shindell et al. calculate this GWP to be 105. If this measure were used the climate impact of methane (e.g. for Plan B above), it would be 5 times the value agreed at Kyoto.

    This is important in assessing the impact of animal husbandry, particulary for cattle and sheep. Are Shindell et. al. right?

    [Response: Of course we are! ;) – gavin]

  21. 221
    Sekerob says:

    Re: 220 Geoff Beacon 13 March 2010 at 2:50 PM

    With mention of Kyoto, if it does carry into various other indices, wonder how this is going to translate into e.g. the AGGI index? A simulation of the before and after per end of 2008 would be nice to see.

  22. 222
    wili says:

    G Beacon. Thanks for pointing out this article. Over 100 times CO2 GWP over a 20 year interval is quite a stunning figure. Do they estimate it for 5, 7, or 10 year intervals?

    On a side note, I don’t understand why you are so dismissive of the role of air travel in GW. Of course it is small compared to coal burning for electricity or meat eating–most of the world uses electricity and eats meat, while relatively few regularly fly.

    But that doesn’t mean that it is benign as an activity, or that it isn’t a huge part of any individuals carbon foot print who flies more than once or twice a year. Am I missing something? Or is the rationalization it looks like.

    [Response: GWP on very short periods is not a useful thing to calculate because the climate system integrates GHG forcings over decades. Even 20 years is a bit of stretch. 50 or 100 year periods are the most relevant for what will actually happen. – gavin]

  23. 223
    Patrick 027 says:

    Re GWPs –

    The decay rate of instantaneous forcing from a unit of emission at one time can change as the compositions and climates of the atmosphere and ocean change, but setting that issue aside (or using an averaged effect for each type of emission over some time period, given some expected scenario):

    The GWP per unit emission, multiplied by the emission rate, gives a GWP per unit time, with units of radiative forcing (or that relative to a standard); if the emission rate is constant over time, then the radiative forcing is approached that is proportional to the GWP per unit emission * emission rate.

    The GWP of methane depends on whether the methane is of fossil C or not, or if it is not fossil C, if it is part of a net removal of C from biomass or soil. If it is either of those, then the CO2 from methane adds to the GWP.

  24. 224
    Patrick 027 says:

    “if the emission rate is constant over time, then the radiative forcing is approached that is proportional to the GWP per unit emission * emission rate.”

    Oops, that’s only if the time period is long enough for the instantaneous radiative forcings of the oldest emissions to have decayed to near zero.

  25. 225
    Steve Bloom says:

    Wili, the material your questions generated has been very informative. Thanks, and please do keep it up.

    Re #s 205/6: Patrick, see last week’s Nature cover article on Pliocene tropical cyclones, one implication of the circulation reorganization we can look forward to if CO2 stays anywhere close to current levels. Also see various recent PRISM papers for details on the reorganization.

    Re #219: Geoff, it’s worth mentioning that we’ll already be in pretty bad shape if sulfate injection starts sounding like an attractive option.

    Re #222 response: Gavin, wouldn’t that integration lag mean we’d be looking at a noticable tropospheric warming pulse in the first decade or so? Any idea what that would be based on the methane release Shakhova postulates?

  26. 226
    Geoff Beacon says:

    Gavin’s response to 222.wili is

    GWP on very short periods is not a useful thing to calculate because the climate system integrates GHG forcings over decades. Even 20 years is a bit of stretch. 50 or 100 year periods are the most relevant for what will actually happen.

    If I understand correctly Myles Allen’s “Towards the trillionth tonne” has an emphasis on “the accumulated total of long-lived GHGs over time” and its “all-important peak”. The timing of the peak concentration of greenhouse gases is more important than it’s timing. (The quotations are from the UK Committe on Climate Change)

    On this analysis when the climate is near the “all important peak” the measurement of short term species over short time-scales will become important.

    But I infer from Gavin’s response that he expects no serious unexpected net positive feedback in the short term. But some feedbacks are happening already with unexpected speed. Peter Wadhams tells me:

    The case of Arctic ice is somewhat of a tipping point since the open water created during summer warms up, to about 5C at present, and this slows down the subsequent autumn freeze up, giving less winter growth. The area of multiyear ice is also shrinking to the point where almost the whole ice cover will be susceptible to summer melt. It may grow back a little in a cold winter but in my view it can never get back to its original situation of, say, 40 years ago. In this sense it has passed through a tipping point

    This may not be the clathrate gun but it has been happing sooner than expected.

    P.S. Sorry I didn’t notice Gavin as et.al.

  27. 227
    Yoron says:

    Is there any research done around what might become a ‘tipping event’ for our Earth. My thoughts is in the direction of methane being that sliver that tips the climate for good. We have had earlier very sharp turnings of the Earths climate haven’t we, like happening over just decades.

    And no matter what we say here we can’t really say how much methane that’s getting loose for the moment. There are all kind of ‘relations/forcings’ building up the climate we see, and i expect them to be able to feed on each other and increase. If that is right, then it isn’t the slow build up that should worry us but the short time ‘rush’ we might get, tipping our Earth irrecoverably.

    So that’s what I’m wondering about. Have there been any experiments, or theoretical studies over what might suffice for creating a ‘tipping point’ for our Earth.

  28. 228
    wili says:

    Thanks again to one and all for great and very pertinent info.

    Geoff at #226 wrote, “The timing of the peak concentration of greenhouse gases is more important than it’s timing.”

    Is there a typo here? I’m trying to understand what you are saying as it sounds quite significant, but I can’t quite follow this.

    I probably won’t post much more here, but to me, as a long term thinker, even if all the sea bottom methane turned to CO2 before it reached the atmosphere, and even if this happened over millennia, if a significant portion of the total did so through the now multiple feedbacks, this would both strengthen and lengthen the warming even, making it all that much harder on the planetary life systems.

    Not good news.

    Of course, the rational response to any of these scenarios is to reduce our added forcing as quickly as possible. But we do not seem capable, collectively, of such a rational response. Do what you can individually and locally, while still putting pressure on national leaders.

    Best to all,
    john “wili” harkness

  29. 229
    Patrick 027 says:

    Re wili 228 – from the context, I’m guessing what was meant was that the timing of the instaneous radiative forcing is more directly important than the timing of the emissions. The later would generally peak earlier than the former (although a sudden-enough drop could increase the forcing in the short term if there is an associated drop in some aerosol emissions – that depending on the emission source).

  30. 230
    Patrick 027 says:

    Re Steve Bloom 225 – sounds interesting, thanks!

  31. 231
    Geoff Beacon says:

    228 wili. Thanks it should have read.

    The level of the peak concentration of greenhouse gases is more important than it’s timing.

  32. 232
    wili says:

    Thanks for the clarification, Geoff.

    If I can task the patience of the community one more time: I note that on sites like http://www.esrl.noaa.gov/gmd/ccgg/iadv/ they indicate levels for CH4c13 at some locals as well as for CH4. Does this isotope tell us about the origins of the methane? Do higher relative concentrations of CH4c13 in the mix indicate a higher or lower level of methane from current biological activity? Or is it an indicator for something else?
    Thanks again.

  33. 233
    PotomacOracle says:

    What’s the scientific evidence show about methane hydrate dissociation in the Arctic or anywhere oil and gas wells have been drilled?

    MBARI’s Dr. Charles Paull, did some work for lots of years in the Arctic and claimed that ch4 could only form where there was freshwater, co2 and methane from decayed material. The hydrates, he said could not be formed in salt water. What was interesting is that these hydrates were dissociating more rapidly than anyone had estimated due to wraming of the tundra and permafrost. This was occuring in many of the locations where oil and gas wells were numerous.

    What’s the consequence? What do we know about the extent to which the oil industry uses fresh water to pressurize wells and leaves it down there for decades. How much? From where does it come? Who loses the water?

  34. 234
    uop online says:

    Great post, I would suggest that you make it a bit handier to share this to some social media sites, throw up a big add to twitter button or something in a few places that are obvious. No sense in making it too much work to add your stuff. Also, I really like your comment layout here, is it the default setup for your theme or did you customize it?