In the early 1990’s, in defiance of IPCC projections, the methane concentration in the atmosphere abruptly stopped rising, and has remained nearly constant since then. Methane is a crouching tiger in the carbon cycle, with potentially enough available as hydrates and from peats to really clobber the Earth’s heat budget. The big question is, will atmospheric methane start rising again?
Climate impact of methane release
The climate impact of methane differs from that of CO2 in that methane is a transient gas, while CO2 accumulates. The climate impact of methane release depends on whether it’s released quickly or slowly, relative to the methane lifetime.
If it’s released quickly, over just a few years or less, there would be a decade-timescale warming spike, followed by a recovery toward the lesser warming from the CO2 that the methane would oxidize into. The amount of available methane is staggering. If just 10% of the ocean hydrate reservoir were to escape to the atmosphere within a few years, it would be the radiative equivalent of a ten times increase in atmospheric CO2, truly catastrophic.
On the long term (longer than a few decades) the transient methane concentration is determined by the chronic rate of methane emission to the atmosphere. A higher concentration in the atmosphere accelerates the overall rate of methane oxidation, to balance the greater input. More methane molecules are standing in line to compete for the limiting supply of the reaction catalyst molecule, OH radical. The oxidation product of the methane, CO2, builds up enough to impact the climate as well. In the long term, the radiative forcing from the accumulating CO2 may exceed that of the transient methane concentration [Archer and Buffett, 2005].
There have been two methane sources in the newspapers in the past few years. One is plants, measured recently [Keppler et al., 2006] to give off prodigious amounts of methane. If this is true, it might imply a small increase in chronic emissions in the future. The seasonal cycle of atmospheric CO2, the breathing of the biosphere, has been getting deeper over the years. If the biosphere is breathing deeper, maybe it’s also farting more.
The other is peats, on which there is a voluminous literature. Peat methane fluxes are notoriously patchy and difficult to generalize, but there are a few things you can depend on. One is that water makes a huge difference; a wet peat soil will emit methane while the same soil, dried, would actually consume methane. Two, there seems to be a reproducible methanogenesis poisoning effect by sulfuric acid deposition (acid rain), caused by the stimulation of sulfate-reducing bacteria displacing the methanogens. Three, melting starts things cooking. Fourth, peats release much more carbon as CO2 than as methane, and their strongest radiative impact will probably be from the CO2.
Methane hydrates are the giant reservoir on Earth. It takes a long time to warm the deep ocean and the clathrate zone, and no one has proposed a mechanism for getting much methane release from hydrates in the coming century. The only place where melting methane hydrates appear to be releasing methane to the atmosphere is on the Siberian margin, where hydrates associated with the permafrost relict from the last glaciation release methane to the shallow water column of the shelf waters.
Industrial emission of methane declined a bit with the collapse of the USSR in 1989 and thereafter. Industrial methane emission arises from leaks, more difficult to pin down than the amounts of deliberately released gases such as CO2. Agricultural emission, from rice farming and ruminant animals, is not so easy to quantify either, but we’ll leave a description of that to the reader’s imagination.
Methane degrades to CO2 by reaction with OH radical in the atmosphere. OH is produced by photochemical reaction with compounds such as ozone and NOx, the concentrations of both of which have been altered by industrial activity. OH reacts with methane and carbon monoxide (CO), the concentrations of both of which have also changed. The chemistry of the atmosphere is analogous to the chemistry in a candle flame, which can burn faster or slower depending on the conditions, for example how quickly it is primed by reactive NOx emission or solar UV (in the case of the atmosphere) or how long the wick is (in the case of the candle). The lifetime of methane in the atmosphere seems like it could quite easily be altered by human activity.
It is impossible to measure the global inventory of OH directly because its concentration is so low and so variable. The tracer for the global OH inventory with the longest pedigree is methyl chloroform, CH3 CCl3. Prinn et al  diagnosed 10% changes of OH concentration on decadal timescale, but Krol and Lelieveld  claim that this result is sensitive to small changes in the assumed source function of methyl chloroform. If the stuff were hoarded a bit before the onset of the Montreal Protocol banning its use, the OH change diagnosed by Prinn could go away. Emission of methyl chloroform stopped in 1992, so the signal now comes down to the decay time constant of the atmospheric concentration. This is complicated by other uptake fluxes such as invasion into the ocean [Wennberg et al., 2004].
The concentration of 14C in CO serves as another tracer for the OH inventory [Manning et al., 2005]. 14C is produced naturally, by cosmic ray neutrons impacting nitrogen gas, and it quickly oxidizes to 14CO, then after a few months to 14CO2. Changes in the solar magnetic shielding of the Earth can affect the production rate of 14CO, requiring a correction, and exchange with the stratosphere is important, but the competing source / sink problems do not appear to be as severe as they are for methyl chloroform. The lifetime of CO in the atmosphere is much shorter than that of methyl chloroform, making the 14CO concentration much more sensitive to, and diagnostic of, month-to-year timescale variability in OH. 14CO varies by factor of two or more over the seasonal cycle, whereas methyl chloroform only varies by a few percent. Manning et al  found no long-term trend, but short-term 10% variations from Pinatubo and Indonesian fires. Pinatubo brought a 12% decrease in solar UV flux [Dlugokencky et al., 1996], decreasing OH, while fires, in particular the Indonesian fire in 1991, bring an increase in CO and CH4 emissions, which can also deplete OH [Butler et al., 2005]. One gets a picture of a volatile but self-stabilizing OH cycle, a flickering flame.
Putting them together
One clue that might help unravel past changes in methane sources is that the rate of atmospheric increase of several gases all correlate. Langenfelds et al  found that CO2, 13C, H2, CH4, and CO growth rates all march in step with the Southern oscillation from 1992-99. Simmonds et al  find similar correlations in data from 1996-2003. Both authors point to fires as a potential common source, as opposed to wetland emissions (which don’t produce H2, for example).
Another seemingly useful clue is that, during a period of methane doldrums (no rise) from 1999-2002, the N/S gradient of methane relaxed a bit [Dlugokencky et al., 2003], suggesting that the doldrum was due to a decline in a methane source in the northern high latitudes. Since most fires burn in the tropics, rather than in the high latitudes, this clue would seem to be pointing us toward wetlands, i.e. in a different direction than clue #1.
A recent paper [Bousquet et al., 2006] attempts to bring all these pieces together into an inverse calculation of the methane sources. This is not a fundamentally new approach, but it does have the advantage of including the most recent several years of data, as methane stubbornly continues to refuse to rise. Changes in OH concentration are diagnosed from methyl chloroform. The spatial pattern of CH4 variations, plus 13CH4 data, provides the basis for partitioning the methane changes among the various sources and sinks.
Their conclusion is that rising human emission since 2000 has been masked by a probably temporary natural decline in wetland emission. Their diagnosed source fluxes are consistent with bottom-up models of wetlands and fires, and independent fossil fuel emissions estimates. But I have to wonder what they’d get if they considered some of the other trace gases mentioned above, such as CO, 14CO, and H2.
What are the implications of all this for our ability to predict the future of the methane cycle? Let’s summarize what you’ve just read. According to one set of papers, atmospheric methane could be suppressed in the future by controlling land fires. Or it could be that methane variations are mostly produced by wetland emission, driven by climate change as well as land use decisions, according to another set of papers. Or methane could resume its rise, toward a new steady state, because it is driven by increasing fluxes from melting permafrost peat and hydrates, according to observations on the ground.
The bottom line I take away from all this is that the available studies come to a strikingly divergent range of conclusions. We know a lot about the methane cycle, but as far as forecasting the near-term future, we have no clue. No one would build a nuclear reactor if our understanding of the underlying chemical dynamics were as fragile as this. Instead, we are taking the reins of a planetary biosphere. This is disturbing.
Archer, D.E. and Buffett, Time-dependent response of the global ocean clathrate reservoir to climatic and anthropogenic forcing, G-cubed, 6,3, doi: 10.1029/2004GC000854, 2005.
Bousquet, P., P. Ciais, J.B. Miller, E.J. Dlugokencky, D.A. Hauglustaine, C. Prigent, G.R. Van der Werf, P. Peylin, E.G. Brunke, C. Carouge, R.L. Langenfelds, J. Lathiere, F. Papa, M. Ramonet, M. Schmidt, L.P. Steele, S.C. Tyler, and J. White, Contribution of anthropogenic and natural sources to atmospheric methane variability, Nature, 443 (7110), 439-443, 2006.
Butler, T.M., P.J. Rayner, I. Simmonds, and M.G. Lawrence, Simultaneous mass balance inverse modeling of methane and carbon monoxide, Journal of Geophysical Research-Atmospheres, 110 (D21), 2005.
Dlugokencky, E.J., E.G. Dutton, P.C. Novelli, P.P. Tans, K.A. Masarie, K.O. Lantz, and S. Madronich, Changes in CH4 and CO growth rates after the eruption of Mt Pinatubo and their link with changes in tropical tropospheric UV flux, Geophysical Research Letters, 23 (20), 2761-2764, 1996.
Dlugokencky, E.J., S. Houweling, L. Bruhwiler, K.A. Masarie, P.M. Lang, J.B. Miller, and P.P. Tans, Atmospheric methane levels off: Temporary pause or a new steady-state?, Geophysical Research Letters, 30 (19), 2003.
Keppler, F., J.T.G. Hamilton, M. Brass, and T. Rockmann, Methane emissions from terrestrial plants under aerobic conditions, Nature, 439 (7073), 187-191, 2006.
Krol, M., and J. Lelieveld, Can the variability in tropospheric OH be deduced from measurements of 1,1,1-trichloroethane (methyl chloroform)?, Journal of Geophysical Research-Atmospheres, 108 (D3), 2003.
Langenfelds, R.L., R.J. Francey, B.C. Pak, L.P. Steele, J. Lloyd, C.M. Trudinger, and C.E. Allison, Interannual growth rate variations of atmospheric CO2 and its delta C-13, H-2, CH4, and CO between 1992 and 1999 linked to biomass burning, Global Biogeochemical Cycles, 16 (3), 2002.
Manning, M.R., D.C. Lowe, R.C. Moss, G.E. Bodeker, and W. Allan, Short-term variations in the oxidizing power of the atmosphere, Nature, 436 (7053), 1001-1004, 2005.
Prinn, R.G., J. Huang, R.F. Weiss, D.M. Cunnold, P.J. Fraser, P.G. Simmonds, A. McCulloch, C. Harth, S. Reimann, P. Salameh, S. O’Doherty, R.H.J. Wang, L.W. Porter, B.R. Miller, and P.B. Krummel, Evidence for variability of atmospheric hydroxyl radicals over the past quarter century, Geophysical Research Letters, 32 (7), 2005.
Simmonds, P.G., A.J. Manning, R.G. Derwent, P. Ciais, M. Ramonet, V. Kazan, and D. Ryall, A burning question. Can recent growth rate anomalies in the greenhouse gases be attributed to large-scale biomass burning events?, Atmospheric Environment, 39 (14), 2513-2517, 2005.
Wennberg, P.O., S. Peacock, J.T. Randerson, and R. Bleck, Recent changes in the air-sea gas exchange of methyl chloroform, Geophysical Research Letters, 31 (16), 2004.
45 Responses to "Rasslin’ swamp gas"
Leonardo Alenadre says
An interesting material to understand the effects of the atmospheric methane over (or against) the nature.
Rio de Janeiro
“Changes in the solar magnetic shielding of the Earth….”
Is there any correlation between the flipping of Earth’s magnetic polarity, with its corresponding weakening of the field’s strength, and global climate? Apparently, the field has been weakening for some years and we may be near a polarity change (or more, as these things changes may flicker a bit before they settle down).
[Response:I haven’t heard evidence or an argument for big climate changes on the magnetic transitions. I guess the question is whether the magnetic field of the earth can affect the solar UV flux. Interesting question. David]
Thanks for that David, from my more limited reading I’d gleaned the same basic notion.
“We know a lot about the methane cycle, but as far as forecasting the near-term future, we have no clue. No one would build a nuclear reactor if our understanding of the underlying chemical dynamics were as fragile as this. Instead, we are taking the reins of a planetary biosphere.”
Indeed. Words like “stupid” don’t really cover our current behaviour.
This year in the UK we’ve had temperatures of 2degC above the average from May to September. http://www.metoffice.gov.uk/corporate/pressoffice/2006/pr20061016.html Some I know have been saying how ‘pleasantly mild’ it’s been. :)
Just now on BBC News 24, we had the Friends of the Earth Director of ‘New Economics’ (whatever that is), conflating temperature projection and melt-driven sea level changes. The end result being the implication of many metres of sea level rise within a matter of several decades. :)
‘Stupid’ seems to be very fashionable at both ends of the spectrum these days.
I find Anthropogenic Global Warming a bit of a mouthful, so I’d taken to calling our misadventure “The Grand Experiment”. As the seriousness of this hit me, it crossed the line into Dr Strangelove style farce. So I changed that to “Operation FUBAR”.
Now I think I’ll call it “Just Plain Stupid”. ;)
pete best says
As the premafrost melts in the arctic tundra then does that mean a likely increase in methane production destined for the atmosphere?
[Response:Yes, that is the expectation. Decomposing peat is a CO2 source too. David]
teacher ocean says
I enjoyed reading this, but let’s see if I understood it correctly because I would like to teach it to my students.. Although we understand, more or less, the role of methane in climate dynamics [very potent greenhouse gas], it is mysteriously not rising in the atmosphere since 1990. We don’t know why it isn’t doing that because we don’t really understand the temporal changes in the volume and fluxes of methane within the multiple reservoirs it is held. So I guess it is something like if you see the seas recede, it doesn’t mean the ocean is getting smaller, it means a tsunami or another big wave is getting ready to hit the shores.. In other words, steady methane concentrations in the atmosphere since the early 90s can’t be good news..
Also, about not building nuclear reactors.. I think we would have to show people would get cancer from global warming before most people consider it worth taking precautions for.. Yes disturbing…
[Response:I don’t know that the steady methane concentration is bad news, like the beach at a tsunami, but you’re correct to conclude that it’s still mysterious. David]
Pierre Allemand says
I am just wondering why dissolution of methane in the ocean has never been considered. Yet methane is slightely soluble in sea water (The Duan Research Group) , and its solubility increases drastically with pressure to reach 0.28 mole/kg in the deep bottom of the ocean (4.5 g/l). This fact allow the ocean to be considered as a giant possible reservoir of methane.
More interesting, fluctuation of methane content in the atmosphere follows very often variation of CO2, and ocean is considered as the most important sink for CO2.
[Response:The concentration of methane in seawater can be measured, and I think the ocean is very often a source to the atmosphere, rather than a sink. Not a large source or sink, though. Methane follows CO2 in the ice core records apparently be coincidence; the CO2 is largely unexplained, while the methane is attributed to wetlands. Methane changes much more quickly than CO2 in the ice core records, through the Younger Dryas for example, which lasted 1000 years, methane goes back to glacial values while CO2 sort of hovers in place. David]
Hank Roberts says
Advanced computer modeling only recently helped understand why the steel in old nuclear plants becomes so fragile so much faster than the designers expected it would. Embrittlement. Fragility. Oops.
Steel in freezing water becomes brittle — but the Titanic went the northern route to cut a few days off of its first voyage, compared to using the warm-water southern route anyway. That form of embrittlement — fragility — isn’t well understood yet.
We’re not being uniquely dunderheaded in failing to imagine fragility in climate. We’re behaving typically.
How can we explain CH4 seasonal variability?
I think it’s not exactly the same than CO2 seasonal variability.
Can we explain it by plants or OH seasonality?
Can a change (if observed) in these short-term and cyclic variations explain the existing stabilisation (or weak increasing) of CH4 atmospheric concentration?
[Response:The seasonal cycle of methane and CO2 are the source of a lot of the information they’re extracting using the inverse methods, like the Bousquet paper. It comes from seasonal cycles of wetlands and every other methane source. There’s also atmospheric mixing factored into it too. David]
Bryan Sralla says
Other important reservoirs for CH4 are organic shales and coals. Methane is sorbed to free organic carbon in organic shales or coals (and probably peats). The higher the total organic carbon content(TOC), the greater the sorption capacity. In the Devonian Antrim shale of the Michigan Basin, at least 50 TCF of biogenic methane (isotopically light) is held in the shale by adsorption. The surprising thing is that this methane is very young. It turns out that the overlying fresh water aquifer in the glacial till (deposited during the last glacial max) helps maintain an enormous biogenic nursery within the underlying Antrim (the anaerobic microbes need fresh water). Much of the methane generated however, is sequestered by the fractured Devonian Antrim shale. These same processes work in shallow coals, where the coal cleats allow influx of fresh water. A type example of this occurs in the Powder River Basin of Wyoming.
[Response:Thanks. If it is young methane, it might be volatile methane. I’d be very interested in reading more about this. David]
Zeke Hausfather says
I’m curious what mechanisms would make wetlands reduce emissions of methane in recent years? Is it primarily due to the elimination of wetlands via land use changes offsetting anthropogenic methane emissions, or are there other factors such as increasing acidification (though my understanding is that acid rain is declining in many areas post-SO2 regulations) or climate change that are supressing methane releases from existing wetlands?
[Response:I’m not expert but rainfall variations also have a huge impact. I guess the bottom line of the methane story is that we are not yet able to confidently answer questions like yours. David. ]
Onar Ã?m says
In the article it is stated:
“If just 10% of the ocean hydrate reservoir were to escape to the atmosphere within a few years, it would be the radiative equivalent of a ten times increase in atmospheric CO2, truly catastrophic.”
For large parts of the Earth’s past history, CO2-levels have been at least 10 times higher than today, with no apparent catastrophe. 450 million years ago the CO2-level was 10 times higher at a time when the climate was even in a cold ice age epoch. How do you explain this?
[Response:I’m sure the dinosaurs were very happy in their tropical world. The question facing humanity is very different: whether we want our world to suddenly change into a tropical world. The ice age in the midst of high CO2, if you’re thinking of the end Ordivician ice age, I don’t know. Maybe there’s a theory, I’m not up on it. ]
Furthermore, if peatlands emit more methane when they are wet and a warmer world mean a wetter world, this implies that warming leads to more methane emissions. Has this positive feedback been taken into account in climate model reruns of climate in the distant past? E.g. 550 million years ago CO2 was a whopping 18 times higher than today, and it was significantly warmer, meaning that methane levels must also have been much higher too.
[Response:This sounds plausable. I don’t think we could predict it reliably, though. David]
Ian Forrester says
The rate of methane release from wetlands depends on a number of factors. Firstly, the rate of anaerobic methane formation (methanogenesis) will be related to temperature. As the wetland increases in temperature in the anaerobic zone methane production will increase.
Secondly, methane will be oxidized in the aerobic zone (methanotrophs). This too will increase with increasing temperatures. However, the populations of the methanotrophs will always lag behind the rate of methane production until equilibrium is reached.
Thirdly, the rate of methane oxidation is limited by the diffusion of oxygen into the sediments or wetlands. As the temperature increases and the sediments dry out the rate of methane oxidation will increase since the rate of oxygen diffusion will increase.
Thus we can summarize by suggesting that increasing tenmperatures will result in an initial increase in methane emitted by the wetlands. Later, populations of methanotrophs will increase and oxygen will become more available thus increasing the rate of oxidation resulting in a net decrease in methane reaching the atmosphere.
Steve Sadlov says
In the industrialized world, there is less production of the sorts of waste products which yield methane than there was 30 years ago. Recycling programs and other waste reduction efforts have slowed the growth of landfills. Meanwhile, sewage management has changed dramatically. Methane is now mined from the existing landfills and from an increasing percentage of sewage treatment plants – energy costs have driven and will continue to drive some of this not to mention self defense against litigation due to the safety issues of methane. I can only foresee these mechanisms becoming more prominent, at some point resulting in massive recovery of human (and perhaps even agricultural and pastoral) activity generated methane. That would leave the “natural” stores of it in terms of the calculus.
[Response:It does seem like reducing methane leakage would be a relatively easy and beneficial step. David.]
Dan Hughes says
#7. This statement; “Advanced computer modeling only recently helped understand why the steel in old nuclear plants becomes so fragile so much faster than the designers expected it would. Embrittlement. Fragility. Oops.
is an incorrect characterization of the state-of-the-art in understanding of neutron irradiation embrittlement of reactor pressure vessel materials.
The first three references in the article are to rules, regulations, and guidelines published in the late 1980s. Years, on the order of a decade, of work and study almost always precede such publications. Neutron irradiation embrittlement of metals has been a well-known and studied process for several decades; from at least since the 1970s and very likely earlier. Nuclear reactors have powered submarines since 1954, and irradiation embrittlement was certainly known at that time.
Re #10 (Zeke): The Bousquet paper attributes the wetland reductions mainly to temporarily drier conditions in the regions of interest.
What this means for the future is difficult to predict: rainfall is projected to increase, as is temperature, both of which lead to more methane emissions, but some models predict a drying out of soils which would reduce said emissions… I guess we’ll find out.
Eli Rabett says
The chemical dynamics and kinetics of methane are well understood. It is the biogeochemical cycles that produce and absorb methane where the uncertainty resides.
[Response:Biology is what makes it so hard, I believe you’re absolutely right. David. ]
I’m puzzled by the fact that flaring or engine burning of coalbed methane earns a ‘carbon credit’. If methane has 21 times (or thereabouts) the GHG effect of CO2 then we want the amount flared to be less than 21 times the natural unburnt seepage. I suspect that human assisted coalbed methane release is hundreds of times the natural level. We are told that methane capture and burning is a net positive because gas escape is inevitable. On the other hand we are told there is little chance of gas escape when captured CO2 is sequestered under pressure in sedimentary rock, though admittedly they claim to use less permeable rock. The money involved in the methane burn credit is quite substantial; I believe the World Bank recently paid millions to some Chinese coal mines.
[Response:I can’t speak to the specifics but I agree it’s slippery. I’m also suspicious of forest growth credits. David. ]
Jim Dukelow says
Hank Roberts comments — “Embrittlement. Fragility. Oops.” — might seem to suggest that neutron embrittlement and cold embrittlement have recently come as a great surprise to reactor designers and regulators. This is not the case. Although engineers may not have had a full understanding, at the level of crystal structure, of the causes of embrittlement, they have been fully aware of the phenomena for a number of decades and their designs and in-service inpection regimes are aimed at mitigating the associated risks.
Awareness goes back to at least WWII, when some Liberty Ships sailing in the cold waters of the North Atlantic broke in half due to temperatures lower than the nil ductility transition temperature (NDTT) of the steel used in the hulls. The NDTT is the temperature above which an overstressed structure will fail by stretching (ductile yielding) and below which it will fail by brittle fracture. Also during the war, a liquified natural gas storage tank in Cleveland failed catastrophically. The natural gas spread through the urban neighborhood, evaporating as it went, reached an ignition source, and exploded, killing around 130 people. After these experiences, designers used different steels, with lower NDTTs, and there were no more Liberty Ship or cryogenic tank failures.
Similarly, the importance of the NDTT and accident sequences in which it might be important were recognized early on in the nuclear reactor era. Certainly, it was fully recognized when I studied nuclear engineering 33 years ago. A qoutation from Hank’s first link gives some of the flavor:
“Early recognition of the importance of embrittlement by regulators and the nuclear industry led to RPV surveillance programs. Many reactors include capsules containing representative steels that are located on the inside of the RPV where the [flux] is several times higher than in the vessel itself. Thus, the surveillance data are used to provide early estimates of the embrittlement of a given vessel, and collectively represent a database for assessing and predicting embrittlement. Numerous accelerated test-reactor studies have also been conducted.”
Typically, at each refueling, a few of these steel capsules will be removed from the reactor and tested using the Charpy V-notch impact test, a standard diagnostic for embrittlement. In the event of unacceptable embrittlement, a possible mitigation and RPV life extension strategy is vessel annealing — raising the temperature to 600 deg C for several hours. If memory serves, some of the Russian RPVs have been annealed. Annealing is not simple and it is not clear exactly how much life recovery it provides.
Hank’s second link is broken. If you go to http://www.eere.energy.gov and search on “embrittlement”, one of the hits is a FAQ sheet “Cold Work Embrittlement of Interstitial-Free Steels”, which is probably what was once behind the broken link. Here the concern is preventing embrittlement of cold-worked steels — as-rolled and high strain, deep drawn steels. Although not described in this FAQ, there are also NDTT concerns for steels used in cryogenic conditions in a hydrogen economy.
Hank Roberts says
Dan, you’re right that looking forward we know more — but fission plants built before this problem began to be understood are expected to run for many years yet, and the last ones built should have incorporated what was then known. They didn’t, as far as I know. It would be foolish to build a 1950s-era design now. It was foolish when the last of them were built, old designs keep being used even when science has already found their flaws.
Current plans are to build many more coal burning plants, without taking into account what we now know about climate.
Lawrence McLean says
Re #11 (Onar): I have seen these statements by other contrairians. My questions are:
1. Is it actually correct that the CO2 level was indeed ten times higher than today?
2. If the CO2 level was higher, what was the climate actually like when the CO2 level was high, was is lush and wet or was it desert?
3. What was the solar flux in those periods?
Andrew Alcorn says
If methane is emitted by plants in prodigeous quantities, is reduced growth, in, for example, the Amazon forest due to higher temperatures and drought, a candidate for explaining the drop in methane emissions from the early 1990s?
[Response:My hunch is, my reading between the lines of the literature, that most of the methane community is waiting for that plant result to go away. I get the impression it doesn’t fit the rest of the budget very well, and so is viewed with a wait-and-see skepticism. So I’d say that sure, it could turn out to be an answer in the end, but it’s not on the top of most people’s lists. Just my impression. David. ]
Blair Dowden says
Re #11: According to this summary at Physorg.com, recent data has shown that the late Ordovician ice age started 10 million years earlier than was previously thought, which places it during a time of relatively low carbon dioxide levels, and has it end when carbon dioxide levels were higher. So your information may be out of date.
Ike Solem says
Methane generation is associated with anoxic conditions, and those anoxic conditions can be associated with both biological and physical effects and systems. The recent low-oxygen dead zone off the Oregon coast is a good example. Is the effect caused by high biological oxygen demand due to warmer waters? Is less oxygen being mixed into the water due to slowed thermohaline and wind-driven circulation, and if so is a major change in ocean circulation underway, or is this a new seasonal effect? Is it partially due to the fact that human nitrogen fixation (ammonia/nitrate fertilizer production using natural gas) now accouts for something like twice the amount fixed by natural processes? People have been turning lakes and ponds into eutrophic green pools with anoxic sediments for decades now; is the ocean starting to reflect this?
“Hypoxic event ends off Oregon coast
CORVALLIS, Ore., Oct. 30 (UPI) — U.S. scientists say the longest, largest and most devastating hypoxic event ever observed in marine waters off the Oregon Coast has finally ended.”
Re# 17, it seems that the isotopic signature of atmospheric methane could tell you something about it’s source. Methane concentration has about tripled since pre-industrial times – where does the excess come from? Here are some more abstracts on the issue:
“Concentration and 13C records of atmospheric methane in New Zealand and Antarctica: Evidence for changes in methane sources” Lowe et al 1994
“The isotopic composition of atmospheric methane” Quay et al 1999
(This study suggests that ~18% of atmospheric methane in 1999 is from fossil fuel sources)
How much of the CO2 in the atmosphere today was once atmospheric methane that was oxidized to CO2? Stable isotope ratios in atmospheric methane and carbon dioxide provide a window on the sources as well.
For a discussion see http://adsabs.harvard.edu/abs/2003TrGeo…4..175Y :
With respect to predicting the biosphere’s reponse to/effects on climate change, this quote is very appropriate; it’s certainly a good argument for the need for well-funded data collection programs:
“It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts.”-SH.
RE #11: “550 million years ago CO2 was a whopping 18 times higher than today”
You are comparing today’s CO2 levels to the CO2 levels that existed during the “cambrian explosion”, a time when multicellular fauna started emerging (and farting), how is that long lost world even relevant to auditing CH4 in today’s biosphere?
Here is some similar “logic” twisted in the opposite direction: The fact that humans did not exist 550mya demonstrates that humans cannot coexist with 18X higher CO2 levels.
Dan Hughes says
#19. You continue to mis-characterize the status of nuclear power plants relative to neutron embrittlement. All such power plants have within the reactor pressure vessel a neutron shield placed between the fuel region and the stressed pressure vessel. As the name suggests the purpose of the shield is to reduce the neutron flux reaching the pressure vessel materials. As metioned in #18 above neutron embrittlement has been a known and understood phenomenon for decades. All plants have been designed and built with the understanding that neutron embrittlement will occur and the designs have accordingly accommodated for its occurrence.
No fission power plants were built before the ‘problem’ was understood. Additionally, these statements are simply not correct; ” … and the last ones built should have incorporated what was then known. They didn’t, as far as I know. It would be foolish to build a 1950s-era design now. It was foolish when the last of them were built, old designs keep being used even when science has already found their flaws.” All plants did incorporate what was known at the time. No one has ever sugested that new power plants be based on ‘1950s-era’ technology. Instead, the designs of newer plants was started in the 1990s and is underway even now. With the exception of demonstration and proof-of-concept experiments, few ‘1950s-era plant’ were built for base-load electricity production. No plant has ever been designed and built without full recognition of all that is known about the processes and phenomena that are important.
Many operating plants have, and others very likely will, apply for extension of their operating premits for a copule of decades beyond the original length of operating permit. These permits will be issued with the complete understanding that neutron embrittlement occurs.
I suggest that you go to http://www.osti.gov and do a few literature searches.
“Two, there seems to be a reproducible methanogenesis poisoning effect by sulfuric acid deposition (acid rain), caused by the stimulation of sulfate-reducing bacteria displacing the methanogens.”
Okay, I’m a fairly bright person, but like most Americans, my science background is not strong. I have no idea what that statement means. I try to keep up with realclimate to understand what’s going on, but have often run into statements like the one above. Maybe I lack the intellectual rigor to benefit from the site.
All I know is that you guys are losing me. How am I supposed to relay that sort of information to a layman sceptic? I don’t expect you to write on a ‘Dick and Jane’ level, but perhaps something a little more layman friendly. Or maybe I’m not a bright as I think, or I’m on the wrong website.
[Response: Sorry! We do occassionally revert to type. The translation is that the little bugs that make methane in swamps get out-competed by other bugs that like acid rain (which is related to sulphate aerosols – mainly from power stations) – so more industrial pollution, less methane emission (everything else being equal). -gavin]
Re: #17 (Johnno): My understanding is that most of the coalbed methane being extracted and burned is from coal seams that are due to be mined in the next couple decades. In which case, it isn’t natural seepage that you need to compare to, but rather the case where miners open up the seam and deliberately vent all the methane to the atmosphere (in order to reduce the possibility of gas explosions underground).
There may be some coalbed methane extraction projects where the coal isn’t ever going to be mined, but I think that number is likely to be small… Though there are all sorts of tricky questions involved in methane projects. For example in manure pit operations (which get a lot of CDM credits) the methane would never have been produced in the first place in a free-range farm. So are you effectively subsidizing a shift from free-range to intensive farming operations? Also, it turns out that some coalbed methane programs contiminate local water sources with various salts. For various reasons, I personally think that methane reduction programs should be separated from CO2 reductions, rather than allowing trading, but I may be a minority viewpoint right now.
Bryan Sralla says
Re: #9, David, here are a few references on biogenic methane and its sorption in shales and coals. Active biogenic methanogenis is widespread in shallow fresh water aquifers thoughout the planet. Much of this gas is believed to become sorbed in high TOC shales and coals, but some is released to the atmosphere.
Arri, L. E., D. Yee, W. D. Morgan, and M. W. Jeansomme, 1992, Modeling coalbed methane production with binary gas sorption: Society of Petroleum Engineers, SPE Paper 24363, p. 459472
Balabane, M., E. Galimov, M. Hermann, and R. Letolle, 1987, Hydrogen and carbon isotope fractionation during experimental production of bacterial methane: Organic Geochemistry, v. 11, p. 115119.
Budai, J. M., A. M. Martini, L. M. Walter, and T. C. W. Ku, 2002, Fracture-fill calcite as a record of microbial methanogenesis and fluid migration: a case study from the Devonian Antrim Shale, Michigan basin: Geofluids, v. 2, p. 163183.
Dellapenna, T. M., 1991, Sedimentological, structural, and organic geochemical controls on natural gas occurrence in the Antrim formation in Otsego County, Michigan: Master’s thesis, Western Michigan University, Kalamazoo, Michigan, 147 p
Martini, A. M., J. M. Budai, L. M. Walter, and M. Schoell, 1996, Microbial generation of economic accumulations of methane within a shallow organic-rich shale: Nature, v. 383, p. 155157.
Martini, A. M., L. M. Walter, J. M. Budai, T. C. W. Ku, C. J. Kaiser, and M. Schoell, 1998, Genetic and temporal relations between formation waters and biogenic methane: Upper Devonian Antrim Shale, Michigan basin, USA: Geochimica et Cosmochimica Acta, v. 62, p. 16991720.
Oremland, R. S., 1981, Microbial formation of methane in anoxic estuarine sediments: Applied Environmental Microbiology, v. 42, p. 122129
Sassen, R., I. R. MacDonald, N. L. Giunasso Jr., S. Joye, A. G. Requejo, S. T. Sweet, J. Alcala-Herrera, D. A. DeFreitas, and D. R. Schink, 1998, Bacterial methane oxidation in sea-floor gas hydrate: significance to life in extreme environments: Geology, v. 26, p. 851854
Scott, A. R., W. R. Kaiser, and W. B. Ayers Jr., 1994, Thermogenic and secondary biogenic gases, San Juan basin, Colorado and New Mexicoimplications for coalbed gas producibility: AAPG Bulletin, v. 78, p. 11861209
Walter, L. M., J. M. Budai, L. M. Abriola, C. H. Stearns, A. M. Martini, and T. C. W. Ku, 1996, Hydrogeochemistry of the Antrim Shale, northern Michigan basin: Annual Report, Gas Research Institute, GRI-95/0251, 173 p
Walter, L. M., J. McIntosh, A. M. Martini, and J. M. Budai, 2001, Hydrogeochemistry of the New Albany Shale: Gas Research Institute, GRI-00, 0158, 58 p.
The numbers just don’t add up. Trillions of cubic feet of coalbed methane are pumped in the US each year from an industry that is much smaller than coal mining. If coal mining emitted anywhere near that level it would dwarf all other sources of methane and atmospheric levels would be much higher (easily 5 ppm, maybe higher).
Perhaps someone with a better background on geology could explain why there’s so much more methane extracted per unit of coal resource in coalbed methane than is vented in regular coal mining.
Re #29 (yartrebo): Two points: First, upon further examination, I found that in fact credits are usually given for “Coal Mine Methane” which is considered the subset of “Coal Bed Methane” that are in seams meant to be mined. So clearly, there is in fact some amount of extracted coal bed methane that would otherwise be nowhere near release, and therefore not eligible for GHG reduction credits.
However, for specific numbers: US Coal mine emissions were on the order of 4 Tg/year in 1990, which is about 0.2 trillion cubic feet, if I’ve done my conversions right (1 Tg methane = 52 Billion cubic feet). We’ve reduced those emissions by about 40% since then despite growth in the coal sector, which, if we assume that reduction is all due to CMM programs, implies about 0.1 trillion cubic feet of methane, so not your “trillions” but not insignificant. Also, globally vented coal mine methane is apparently responsible for about 6% of the anthropogenic contribution or order 20 Tg, which means a trillion cubic feet globally.
But to sum up: I was wrong in my initial comment. =)
Bryan Sralla says
Re #29: Methane production from coal is determined largely by two variables. First is the gas content of the coal measured in standard cubic feet per ton (scf/ton). Second is the rate of gas diffusion out of the coal measured in thousands of cubic feet per day(MCFPD). Both these variables are largely a function of pressure. The higher the pressure, the greater the potential gas yield of a coal. Since the rate of gas flow is controlled by the pressure drop across the face of the coal, the higher the initial pressure in the coal, the higher the rate in which gas will flow out of it.
Now for mining, most coal mining is done at or near the surface. The depth of a mine is limited in many areas by the ability to pump water out of the mine, and the competancy of the rock surrounding the coal. Therefore coal mines are usually shallow (many on the surface), so the coals have low gas contents, and low pressure. Both of these variables greatly limit the amount of methane which diffuses from the coal,into a shallow mine. For this same reason, very little gas diffuses out of a coal exposed on the surface.
To overcome these limitations, wells are drilled into deeper coals with higher gas content and much greater pressure. This allows much larger volumes of gas to be produced from these wells at greater rates relative to most mines.
Isaac Held says
A recent paper on the leveling off of methane that people may be interested in is one by Fiore et al .. In their model this leveling is primarily due to an increased sink associated with climate change rather than changes in sources. About one-third of the sink is due to the temperature dependence of the destruction of methane by OH, the other two-thirds to an increase in OH itself. The increase in OH is due to an increase in lightening, strikingly (sorry about that.) The latter is obviously highly uncertain and parameterization dependent. But the temperature-dependent reaction rate part is relatively solid as I understand it. It is obviously pretty important for future projections to understand if this leveling off is in part related to warming, as it is in the Fiore et al. model.
[Response:Thanks, this is a good paper I guess I missed in my reading. It comes to yet another conclusion, reinforcing my own feeling that we are a long way away from being able to forecast future methane levels. David]
Stephen Berg says
A nice animation of the basics of the greenhouse effect and the effects of human activity on enhancing the effect:
Onar Ã?m says
Re #20, #22
According to both actual measurements and models (GEOCARB) the CO2-levels were some 4000 ppm 450 million years ago, and even as high as 7000 ppm 550 million years ago. There is no single climate associated with high CO2 because in the 500 million year time scale there is no correlation between CO2 and climate.
As to the possible finding that the Ordovician ice age started 10 million years earlier, I don’t see how this matters. CO2 was high during the period from 600 million years ago to 400 million years ago. Only 300 million years ago did CO2-levels reach something that resembles modern levels.
Here is a rough overview over climate change and CO2-change over the period. As you can see there is no correlation. (Veizer’s reconstruction gives no correlation either.)
Steve Hemphill says
During this continental drift layout there is a correlation between temperature and CO2. However, temperature change leads CO2 change. The statement that CO2 increase leads to further temperature increase as feedback is hubris. There is no actual indication outside the isolated laboratory that this is true.
[Response: It’s not hubris, it’s physics. Those scientists and their lab experiments… whatever will they think of next? – gavin]
It amazes me that contrarians regularly refer to temperature levels from 500 million years ago as though they were reliable established fact, but just as regularly deny our ability to reconstruct temperature just 1000 years ago.
Actually … no, it doesn’t amaze me.
Steve Hemphill says
Re the response to #35, another example: Water vapor is also a ghg, proven in the lab. However, with convection it produces clouds. With an increase in convection which occurs with an increase in ghg’s, holding more heat near the surface, more clouds will form, correct?
A simple output of models should be a quantification of overall cloudiness. How does that compare with the quantification of overall temperature?
Mike Doran says
Methane hydrates when they unform–sensitive to regional hydrology changes, are consumed by microbial life and converted eventually to CO2. Then CO2 has a CONDUCTIVITY meaning on a living earth. In regards to post number 2–there is an electrics theory of climate. You can hear audio about it here on the Talkin Tropics show:
I am 20 minutes in and twenty minutes in all the shows where my name is listed in the archives:
Apologies for another off-topic question. I would be interested in your opinion on the relative contribution to climate change made by: a) carbon emissions from aviation and b) methane emissions from livestock. In the UK the former are estimated at approximately 8 millions tonnes/yr, whereas methane emissions from livestock are approximately 1 millions tonnes/yr. Depending on who you believe methane is 23-62 times more greenhouse active than carbon dioxide. But much aviation-associated carbon dioxide is emitted at high altitude, and this has been suggested to enhance the “greenhouse-activity” of CO2. Of course, both aviation and livestock farming give rise to other greenhouse gases, notably nitrous oxide. But in general terms how would you compare the potential effects of these industries on climate change? Also, do you believe that limiting methane emissions from the world’s 1 billion plus cattle through a vaccine or dietary manipulation would represent a meaningful step to mitigating climate change? Many thanks.
The enhanced effect from high-altitude flights comes from the formation of contrails. AFAIK, the CO2 emitted is no worse than that emitted from ground sources.
With regards to cattle, methanogenesis is what powers their gut bacteria that converts otherwise indigestible cellulose into usable energy for the cow. The cow would starve to death (on a grass diet at least) if the methane emissions were eliminated. Considering that cattle are extremely inefficient to raise (partly because a lot of the cow’s food does end up as methane), a better solution would be to have less cows around.
Re #40: The “less cows” approach raises a few questions, though. Does the domestic cow produce more methane than other grazing animals? In particular, more than the American buffalo? (Closely enough related that there have been various attempts at commercializing “cattalo” hybrids.) What’s the difference in numbers/methane production between the immense buffalo herds reported pre-settlement, and cows now?
The methane problems are limited to a specific group of animals called ruminants. As far as the bison herds go, they were orders of magnitude less numerous than the current cow herd (~10 million bison vs ~1 billion cows).
Bryan Sralla says
In another post (which was shut down for being off topic), John L. McCormick asked me why pumping CO2 into a coal causes it to produce more methane. The reason for this is that coals generally have greater (2X) affinity for adsorbing CO2 than for methane. Therefore, by saturating a coal with CO2, the methane is preferentially displaced. The CO2 remains sequestered in the coal by adsorption. This process also works in organic shales. Organic shales and coals have an enourmous reservoir capacity for CO2. For a shale, its CO2 storage capacity in standard cubic feet can be calculated by: (shale density)(volume)(adsorption capacity). The density of most organic shales is around 2850 tons/acre foot. For a shale that is 300 feet thick, covering 250 square miles, having a CO2 sorption capacity of 150 scf/ton, one can observe that the storage capacity is large. As a result of injecting this CO2, if say 50 scf/ton of methane were displaced from this shale, one can also see that these numbers are large too, hence the research by petroleum companies. The challenge is injecting a meaningful rate of CO2 at pressures under the fracture gradient (this usually requires numerous wells). If the fracture gradient is exceeded, care must be given that the stress relationships (Young’s modulus/Poissons ratio) do not cause the initiated fracture to break through to another formation, and thereby leak the CO2.
Lynn Vincentnathan says
Great post on the other main GHG, which maybe a smaller & shorter portion of the problem, but could portent perhaps even more serious problems (or faster warming, if it does start rising, & rising quickly) & sh not be neglected.
Could you translate this into English: “there seems to be a reproducible methanogenesis poisoning effect by sulfuric acid deposition (acid rain), caused by the stimulation of sulfate-reducing bacteria displacing the methanogens.” I take it to mean sulfuric acid suppresses methane going into the atmosphere.
If so, then the reduction of sulfur dioxide (& sulfuric acid) from cleaning up our human emissions, would also have an effect of allowing more methane into the atmosphere. Or am I reading this incorrectly.
Of couse, we wouldn’t want to stop cleaning up our pollution, since sulfuric acid is also a killer of lakes, trees, soil, property, and people.
[Response:You read it correctly. Sulfate is a feedstock for sulfate-reducing bacteria, so acid rain feeds them. Reducing sulfur emissions also stops the cooling impact of sulfate aerosols. David]
Lynn Vincentnathan says
Okay, my previous Q was answered in #26.
Another idea. I think GW will cause more WV & precip, esp in the higher latitudes. I think maybe even more severe flooding – when it rains, it pours. This would probably have some impact on methane (as mentioned wetter conditions cause more releases). However, I think they say it’ll be dryer in the lower latitudes, which may have the reverse effect. However, since WV & precip will net be greater, then I’d guess we could expect methane releases to be greater.
This is probably way too simplistic, considering all the other chemical reaction stuff.