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Une surprise pour les scientifiques !

Classé dans: — gavin @ 11 janvier 2006 - (English)

De temps en temps, un papier scientifique crée de véritables surprises. Les résultats de Keppler et al. publiés cette semaine dans la revue Nature est clairement un de ceux-çi. Ces auteurs ont prouvé qu’un processus jusqu’ici non reconnu fait que les plantes vivantes émettent du méthane (CH4, le deuxième gaz à effet de serre après le CO2), dans des quantités qui semblent être très significatives globalement. Ceci étonne de deux manières – premièrement, l’émission de CH4est normalement associée aux environnements anaérobies (c’est-à-dire pauvres en oxygène) comme les marais ou décharges, alors que la chimie dans les plantes est généralement considérée comme étant ‘aérobie ‘ c.-à-d. non limitée en oxygène, et deuxièmement, parce que les évaluations initiales de cet effet (entre 62-236 Tg/an sur une source totale de 500+ Tg/an!) donne des valeurs qu’il sera difficile d’incorporer dans le budget total du méthane sans des ré-évaluations majeures (et ce malgré les incertitudes liées au budget total – voir l’évaluation de celui-ci par le GIEC).

Les réactions jusqu’ici ont été réservées, et il y aura assurément un grand nombre d’études pour vérifier et raffiner les évaluations de l’importance de ce processus. Une fois que la poussière se sera redéposé, la situation pourrait ne pas être si différente que celle précédent cette étude – certaines émissions pouvant s’avérer avoir été mal interprétées, cette source pouvant ne pas être aussi importante que suggérée par ces évaluations initiales (10-30% de sources totales), ou au contraire elle pourrait radicalement défier notre compréhension actuelle des sources et puits du méthane. Cependant, le processus par lequel cette étude sera confirmée ou pas démontrera clairement que la méthode scientifique est belle-et-bien vivante dans les sciences de climat. C’est-à-dire, aussi longtemps qu’un travail est soigné et rigoureux, et que les conclusions sont justifiées, les papiers bousculant le courant de pensée dominant peuvent paraître dans les journaux les plus importants, et ont une bonne chance à la fin d’être accepté par le reste des scientifiques (si les conclusions tiennent la route bien sûr !).

45 Responses to “Une surprise pour les scientifiques !”

  1. 1

    It is known that plants emit a lot of oxigenated volatile organic compounds, of which methanol is one of the main compounds. Maybe the point is in nighttime lack of oxidation, as photosynthesis is stopped, but methane synthesis as precursor for methanol still is functioning… VOC production also increases in stress situations (like cutting grass, wounding trees).

  2. 2

    #1: It’s quite unlikely that methane would be a precursor to methanol as it’s volatile. You are correct that plants make a wide variety of oxygenated and non-oxygenated hydrocarbons, though they originate from very different sources: Methanol emissions are associated with bud break in woody tissues, C6 alcohols are associated with green tissue damage, C5 isoprenoid emissions are light-dependent while C10 and larger isoprenoids are usually light independent. It’s hard to imagine who methane emissions would fit in with any of these known emissions pathways. This is certainly interesting data worth further study!

  3. 3
    Ender says:

    It seems like a big thing to miss. What if it is a recent phenomenon brought on by environmental changes. I mean if plants have always emitted methane then you would have expected to methane level to rise so it must be accounted for by some part of the carbon cycle.

    It makes more sense if it is only recent. Perhaps it has been missed because up until now it has been so small to be unmeasurable.

  4. 4
    Ender says:

    The last line should read:

    Perhaps it has been missed because up until now it has been so small to be measurable.

  5. 5
    John Monro says:

    Yes, it is interesting that what is rather an arcane piece of research in plant physiology has had so much publicity. It was the first item on our national radio news this morning here in New Zealand – the global significance of the findings was already taken as given, and it was breathlesslessy stated that the findings had come as a “bombshell to the Kyoto agreement”. In this overheated environment do I detect the hand of global warming sceptics in business and the media at work, gleefully sowing the seeds of confusion?

    [Response: I suspect this is just std journalistic confusion and/or pumping up an exciting story: the Grauniad here has much the same: see here – William]

  6. 6
    Tom Huntington says:

    This article raises several interesting points related to potential feedback amplifications to warming. The authors note that the release of methane increases with increasing temperature. They also note that CO2 fertilization resulting in increases in NPP would likely increase methane emissions. Similarly, expected future increases in precipitation and length of growing season would tend to increase methane production. The noted positive relation between irradiance and methane release is also interesting given recent trends showing a reversal of global dimming [Wild et al., Science 2005, Vol. 308. no. 5723, pp. 847 – 850].

    [Response: The results show increasing emissions as temperature rises, which implies that the feedback is positive -however, the ‘standard model’ of methane emissions from wetlands also has that sign of feedback. Therefore any re-assignment of sources may not effect the implied climate response that much. However, all of these calculations require some more detailed accounting before these speculations can be properly quantified. -gavin]

  7. 7
    Pascal says:

    Interesting study, but this is also interesting to examine the global C balance of terrestrial plants.
    The global carbon stock of terrestrial plants is 500 GtC.
    If we imagine a 10% increasing of this stock , this represents 50GtC.
    If we imagine also a thirty years growing this represents 50/30= 1.67GtC/y.
    In CO2 this is equal to 6.11Gt/y of CO2 taken off the atmosphere.
    For the CH4 , 10% of all the plants , emit 0.1*150MtCH4/y = 15 millions tons of CH4/y.
    This CH4 is 23 times more efficient than CO2 for the GH effect.
    So the CO2 equivalent of this CH4 is 345 millions tons/y.
    If we compare to the 6110 millions tons of CO2/y, the balance remains in favour of plants as a way to stabilize atmospheric CO2, for example for energy output.

  8. 8
    Lynn Vincentnathan says:

    I’ve always thought the best way to reduce GHGs is through energy efficiency/conservation and alt energy. Reduce, reuse, recycle, etc. I always did think planting more trees & plants was sort of a cop-out for the real work that needs to be done, and certainly should not replace that work.

    Now what would this say re biofuels & ethanol? I always thought they too were somewhat cop-outs for the more important work we need to do. Even without figuring these surprising methane emissions, I think these fuels may possibly entail greater GHG emissions than they offset — in the manufacture of pesticides, fertilizers, farm equipment; irrigation water & energy to pump it; transporation of bauxite from S. America (harming rainforests) to make farm equipment, ag schools, secretaries, and all the paper work at each stage…the list goes on & on & on.

  9. 9
    Jeffrey Davis says:

    I don’t see the consequences to this. It’s a “rob Peter to pay Paul” kind of thing. The amount of methane in the atmosphere doesn’t increase as a consequence. It just means that other sources of atmospheric methane have been miscalculated.

  10. 10

    Re: #7

    I think you have to be careful about this as a policy option because it is a one-shot deal. I do not find it plausible that we could keep on increasing the terrestrial plant stocks in this manner indefinitely.

    You would also run afoul of the biodiesel advocates who would start burning all this new biomass because it is “carbon-neutral”. Carbon sequestration needs to be more permanent, like maybe turning it into minerals. I hear there are some minerals that are almost pure carbon – maybe we should be trying to create some of those ;-)

  11. 11
    Marlowe Johnson says:

    I don’t think it’s appropriate to lump all ethanol in the same boat. It is true that ethanol made from corn only achieves a 20-30% ghg reduction on a lifecycle basis; however, ethanol made from sugarcane (in Brazil) or cellulose (which should be economically viable in the near future) has been shown to reduce GHGs by as much as 90% on a lifecycle basis; which is why IMO ethanol will likely play a very large role in the near-medium future in reducing GHG emissions.

    Coming back to the topic at hand — Jeffrey, the significance here is so much what impact the discovery will have on the global methane budget (it doesn’t, as you point out), but rather the possibility that such a significant process could have been overlooked for so long…

  12. 12
    Hank Roberts says:

    I’ve seen only the summary — did they eliminate methane from soil microbes, somehow? I saw that they put a dome down over the plant, then withdrew gas from around it by attaching a vacuum bottle — but wouldn’t that pull up gas from the planting medium as well? Was a gasket around the stem used, to avoid getting gas from the soil? Or the container flushed out? Or was a sample taken from a control with no plant, just the planting medium? Sorry, I haven’t seen the actual study, just descriptions of the conclusion.

    [Response: They did an experiment where they throroughly irradiated the leaves to kill off any bacteria. That should have done the trick…. -gavin]

  13. 13
    Hank Roberts says:

    >irradiated the leaves to kill off any bacteria
    That’d be a different source than the one I was thinking of, the soil microbiota; it’s a good control, but not the only one needed.

    I did a grade school science fair in the 1950s, got beans irradiated at Duke’s Van de Graff accelerator — the bean plants given the low dose grew faster and bigger than the controls, probably due to wiping out bacteria and fungi on the beans (before they sprouted). Unpublished, being 7th grader work (grin).

    I’d expect irradiation per se isn’t neutral, it might enhance growth for a while.

    Well, eventually the study will be available to the rest of us. Of course I’m baffled.

    Reminds me of the fundamental error in building Biosphere II — where they were in a hurry so they didn’t bother with mineral soil and layering, they just filled the whole dang thing with topsoil (and then got severe problems with too much CO2 — and I’d bet they got methane too!) — way too much living soil in proportion to everything else, much of it buried too deep to live.

  14. 14
    vimax says:

    I think we are gradually reaching a point now where other technologies will begin to replace the burning of fossil fuels. We just need one more good price surge in gasoline. Once the price goes over $3.00 a gallon things will change real quick.

    [Response: Do people in the US realise that over here in Germany, the gasoline price is 1.25 Euro per liter, that’s 4.72 Euro per US gallon, which is $5.71 per gallon? To us, $3.00 a gallon sounds like dirt cheap petrol. -stefan]

  15. 15
    Almuth Ernsting says:

    Re: 8,10 and 11 – Biofuels and GW:

    If we take a wider view of biofuels and GW then an even more disturbing picture emerges:

    Palm oil and soya are becoming a rapidly growing source of the bio-fuel sector, which itself is expanding by about 25% a year. They are, to a large extent, grown at the expense of tropical rainforests, particularly in the Amazon and in South-East Asia. Indeed, they are becoming a major driving force for rainforest destruction. See here:

    What does this mean for the climate?

    The Hadley Centre has calculated the massive increase in atmospheric CO2 levels if the Amazon was to die back as a result of global warming (climate models differ on how likely this is, I understand). No doubt, we can get the same if we chop it down to produce bio-diesel to run our cars. I understand that many scientists fear that de-forestation will lead to a ‘tipping point’ after which the hydrological system of the Amazon is so disrupted that neither the survival of the remaining forest nor, presumably, of rain-dependent agriculture is guaranteed. See here:,,1606083,00.html

    In South-East Asia, palm oil plantation are connected not just with massive deforestation but also with the drainage of peat swamps, which catch fires regularly, particularly during El Nino years. A study by Susan Page et al in Nature, vol 420, 7th November 2002 calculated that in one year alone the peat fires in Indonesia produced CO2 emissions equivalent to those of 13-40% of global emissions from burning fossil fuels. This could apparently be stopped if the peat swamps were re-flooded (see an article by Peter Aldhous in Nature Vol 432, 11th November 2004) – but the expansion of palm oil plantations, often for bio-diesel is preventing this and making matters far worse.

    As long as bio-fuels threaten major rainforests and peat swamps, they are becoming a growing threat to the climate and global survival – rather than being a solution (which doesn’t mean that bio-fuels could never be grown sustainably, just that taking a holistic view is rather important).

    Almuth Ernsting

  16. 16
    Pat Neuman says:

    … “the role of natural methane sources in past climate change”, … (Keppler, et al)

    Are the authors suggesting that the enhancement in global temperature by about 5 Deg C near the time of the Paleocene Eocene Thermal Maximum (PETM) 55 million years ago (mya) may have been largely due to a global transformation in vegetation from one associated mainly with a temperate climate to one associated mainly with a tropical/subtropical climate?

    Fossil evidence shows that global vegetation changed around the time of the PETM to mainly tropical and subtropical. A tropical forest existed in Colorado around the time of the PETM, which was habitat for many early primates, and crocodiles roamed parts of the Arctic.

    [Response: Not possible. The amounts of carbon released at the PETM are roughly 3 times the total amount of terrestrial biomass – it therefore needed a completely different source of carbon. – gavin]

  17. 17
    rasmus says:

    I haven’t read the article, but are there any reason to think that there is a trend in the methane emissions from plants? Presumably, there has more or less been some kind of ‘steady state’ over the past, not? Is there a notable decrease in the biomass on Earth (deforestation) affecting the balance (or alternatively, are the plants changing so that their emission have increased)?

    [Response: Well there is a temperature sensitivity and they suggest that deforestation trends might be important, but there are no suggestions that this is responsible for the current long term changes. – gavin]

  18. 18
    Lynn Vincentnathan says:

    RE 8, 11, 15
    There’s another issue re biofuels. They could come down to (if it’s not already happening) fuel for the rich replacing food for the poor and starving.

    The idea of sugarcane refuse or other refuse being used as fuel is a great idea, since it would go to waste (& methane) anyway.

    However, sugar growing itself has some social justice issues, including slavery in some areas, coupled with high morbidity & mortality rates of sugar workers and other exploitations. And, of course, sugar crops might be replacing more nutritious food crops. Oh that sweet tooth! I plead sort of guilty myself.

  19. 19
    Marlowe Johnson says:

    Actually lynn you’ve got it reversed — in Brazil they produce close to 15 billion gallons a year of ethanol from sugarcane and most of it is consumed domestically, so the argument that it’s for the rich doesn’t exactly fly. Incidentally, the reason sugarcane ethanol has such a good GHG impact is precisely because they burn the leftover stalks (bagasse) to power the ethanol production plant (unlike the U.S. where coal is often used).

    On the issue of rich biofuels vs food for poor, IMO it’s better to support sugarcane sharecroppers than oil sheiks in undemocratic regimes, but that’s another argument that belongs on another board (as does this post on biofuels). Moreover, the argument that increased production would displace existing rainforest is, according to some Brazilian colleagues of mine, unfounded.

    On a more topical note, I would be interested to see what impact the added methane would have on the overall lifecycle analysis for biofuels (probably small), since most LCAs only account for farming-related N20 as far as I know.

  20. 20
    Pat Neuman says:

    In 16.

    I asked: Are the authors suggesting that the enhancement in global temperature by about 5 Deg C near the time of the Paleocene Eocene Thermal Maximum (PETM) 55 million years ago (mya) may have been largely due to a global transformation in vegetation from one associated mainly with a temperate climate to one associated mainly with a tropical and subtropical global climate?

    In his Response to my question gavin replied: Not possible. The amounts of carbon released at the PETM are roughly 3 times the total amount of terrestrial biomass – it therefore needed a completely different source of carbon. – gavin]

    However, my question in 16. pertained to an “enhancement” in global temperature (by about 5 Deg C), not the full extent of the rise in global temperature to the PETM.

    From Zanchos(2005), … “During the Paleocene-Eocene thermal maximum (PETM), sea surface temperatures (SST) rose by 5° C in the tropics and as much as 9° C at high latitudes (1-3), whereas bottom-waters temperatures increased by 4° C to 5° C (4). The initial SST rise was rapid, on the order of ~ 10^3 years, although the full extent of warming was not reached until some ~ 30, 000 years (30 ky) later (5)”. … “Rapid Acidification of the Ocean During the Paleocene-Eocene Thermal Maximum” James C. Zanchos, et al., 10 Jun 2005 Science Vol 308.

    My question in 16 involved “enhancement” pertaining to the warming which occurred after the initial rapid rise in SST as described by Zanchos, i.e only that amount of warming beyond the initial 1,000 years of rapid temperature rise.

    Miller, K.G. et. al (Science, 2005) said: “We propose that the early Eocene peak in global warmth and sea level (Fig. 3) was due not only to slightly higher ocean-crust production but also to a late Paleocene-early Eocene tectonic reorganization. The largest change in ridge length of the past 100 My occurred ~60 to 50 Ma (57), associated with the opening of the Norwegian-Greenland Sea, a significant global reorganization of spreading ridges, and extrusion of 1 to 2 x 10^6 km^3 of basalts or the Brito-Arctic province(58). A late Paleocene to early Eocene sea level rise coincides with this ridge-length increase, suggesting a causal relation. We suggest that this reorganization also increased CO2 outgassing and caused global warming to an early Eocene maximum”. The Phanerozoic Record of Global Sea-Level Change (Miller, K.G. et. al.): 25 Nov 2005 Science.

    Perhaps the “extrusion of 1 to 2 x 10^6 km^3 of basalts” … ” ~60 to 50 Ma (57) associated with the opening of the Norwegian-Greenland Sea” had led to the initial surge in global temperatures, and a transformation in vegetation to tropical/subtropical contributed in a substantial way to the additional increase (“enhancement”) of 5° C?

    Questions on methane hydrates and global warming were addressed at RC in Dec 2005. “There is an event documented in sediments from 55 million years ago called the Paleocene Eocene Thermal Maximum, during which (allegedly) several thousand Gton C of methane was released to the atmosphere and ocean, driving 5° C warming of the intermediate depth ocean. It is not easy to constrain how quickly things happen so long ago, but the best guess is that the methane was released over perhaps a thousand years, i.e. not catastrophically [Zachos et al., 2001; Schmidt and Shindell, 2003]. david @ 12:52 pm” Methane hydrates and global warming

    I think some comments in relation to the Dec 2005 RC article on Methane hydrates and global warming would be in order now that there is talk of another source (Keppler et al, 2006).

  21. 21
    Pat Neuman says:

    The figure at the link below shows global average methane from measurements by NOAA’s ESRL GMD. The data indicates that the rate of increase in global methane slowed somewhat after the early 1990s. In consideration of the findings by Keppler on methane being released from healthy vegetation, might the slower rate of increase in measured global methane since the early 1990s be related to the reductions of the world’s tropical rain forests?

    by Pat Neuman

  22. 22
    Terry says:

    Does anybody know how long methane remaines in the atmosphere, i.e., what the half-life of methane is?

    [Response: Roughly 8 years (residence time), though it takes ~12 years for anomalies to decay due to non-linearities in the chemistry – gavin]

  23. 23
    Pablo Almaraz says:

    Regarding the figure of methane evolution from the eighties, mentioned by Pat above, I see a conspicuous drop in CH4 growth rate from 1991 to 1992. I remember a paper from Science (2002, Vol. 296, page 1687) in which a simillar conspicuous worldwide drop in leaf area index (LAI, and hence in vegetation “greening”) was detected during the same period, prompted by the 1991 Pinatubo eruption and the net worldwide cooling it caused. So I wonder, can the sudden drop observed in the world CH4 growth rate be a consequence of the reduced vegetation activity detected during this transient “cool” period? Guess this is rather too speculative, but if you check Fig. 1 of the Science paper and the Figure in the NOAA wepage, they appear to be covarying (look the other drop in 1997 in both LAI and CH4 growth rate). With the new findings at hand, I think it would be a beatiful explanation, wouldn’t it?

  24. 24
    Harry N says:

    So if this study holds up, plants may be considered a forcing if long-term carbon storage doesn’t offset their methane production, and there’s an overall increase in plant life on Earth? It’s interesting that despite no apparent indication that plants are indeed making a net contribution to the current trend, we see articles like National Geographic’s Plants Exhale Methane, Contribute to Warming, Study Says.

    Also, in that article, Lowe addresses the late discovery of this source by saying that “Estimating the total global production of methane and other greenhouse gasses is far from an exact science.”. And that “People who prepare the emission budgets use a bottom-up technology. Someone will make a measurement in a swamp somewhere and simply extrapolate that measurement upwards to represent all the world’s swamps. They’ll measure emissions from a cow or a sheep and extrapolate that upwards to include all of the world’s animals.”

    As you can imagine, there are huge errors. The science is so inexact that you could easily fit a new source like this into the estimates.”

    Is this accurate, or oversimplification of what occurs? One would think that several regional measurements would be made for extrapolation purposes. Also, despite seemingly broad comments about inexact GHG estimates, I’m assuming the measurement of CO2 trends and how much is natural vs. anthropogenic is still considered more exact?

  25. 25
    Lynn Vincentnathan says:

    RE #22, when CH4 (methane) “leaves” the atmosphere, does it change into CO2 (plus…hydrogen?) & does that CO2 stay in the atmosphere for a long time (as D. Archer found, one-fourth CO2 may stay there for up to 100,000 years)?

  26. 26
    Gar Lipow says:

    >Now what would this say re biofuels & ethanol? I always thought they too were somewhat cop-outs for the more important work we need to do. Even without figuring these surprising methane emissions, I think these fuels may possibly entail greater GHG emissions than they offset — in the manufacture of pesticides, fertilizers, farm equipment; irrigation water & energy to pump it; transporation of bauxite from S. America (harming rainforests) to make farm equipment, ag schools, secretaries, and all the paper work at each stage…the list goes on & on & on.

    It depends on how it is done. Biofuels done right can make a contribution – not replacing forests with energy plantations, using three to five crop no-till rotations that include energy crops can produce biofuels sustainably, and increase food production as well. Of course we are not going to produce biofuels in quantities to provide one to one replacement for fossil fuels. You need to greatly increase efficiency. But even if we reduce total world energy consumption greatly (while increasing efficiency so that reducing energy use doe not mean reducing world economic output) – we still have the problem that most renewable sources are intermitten – sun, wind, wave etc. In the absense of much much cheaper energy storage than we are likely to see in the near future, we will need make use of the dispatchable sources pretty much up to their limit to add to the mix. Hence even though geothermal, hydroelecticity and biofuels combined will not provide anything like all even of greatly reduced energy consumption, they will be an important part of the renewable mix, because they are sources that you can use when needed, not just when the wind blows or the sun shines.

  27. 27
    Pat Neuman says:

    In trying to explain varying rates of global methane accumulation over the most recent two decades, I mentioned tropical rain forests as being an element to consider [21]. Pablo Almaraz mentioned a worldwide drop in leaf area index (LAI, and hence in vegetation “greening”) and the 1991 Pinatubo eruption [23] for consideration.

    This morning I reviewed figures at:

    NOAA Climate Diagnostics Center
    Multivariate ENSO Index (MEI)

    Global Average Growth Rate based on CO2 measurements

    I see similar patterns of change as shown at:

    In RC “Scientists baffled!”, Gavin wrote: “Once the dust settles though, the situation may not be so different to before – some emissions may turn out to have been mis-identified, this source may not be as large as these initial estimates (10-30% of total sources) suggest”, …

    In these personal comments, I have gained some limited understanding of climate change from my personal study of what other scientists have learned and documented, here at RC and elsewhere. There are many scientists in the US who have not been telling the public about their findings. I’d like to see contributions by many more scientists in the US, to RC and other public places, particularly those working at (or having worked): NOAA Climate Diagnostics Center, NOAA ESRL GMD, other NOAA offices, National Laboratories and EPA.

    Why haven’t there been contributions to RC from many more scientists who have been working in public service and who are employed by NOAA and other US federal agencies? I think our goal is to save the world. There has to be unselfish cooperation and leadership at all levels of all governments and industries, and the public, all demonstrating sincerity to succeed in making that goal. Who would disagree with that and be justified in claiming they were a responsible human being?

  28. 28
    Ken Robinson says:

    Re: #27
    Pat, you state that “I think our goal is to save the world.”, referring I believe to scientists working in the area of climate change. You ask the question “who would disagree with that and be justified in claiming they were a responsible human being?” As a responsible human being, let me respectfully disagree.

    I think the goal of scientists is to do good science. “Saving the world” presupposes that the world needs saving. It’s a value statement, one which can easily lead to the introduction of bias (intentionally or not) into the process of scientific discovery. Without meaning to rehash old debates, there is significant evidence that many academically qualified individuals have allowed their personal beliefs and agendas to influence their evaluation of what the data are saying.

    Scientists, like everyone else, are entitled to their opinions. Hopefully these opinions are reasonably well-informed. But the goal should be to accurately report the state of the world, whatever that state may be. Being determined to “save the world” certainly risks a loss of objectivity. Do you not agree?


  29. 29
    Pat Neuman says:

    re 27.

    Our (humankind’s) goal is to save the world. The world needs to be saved from our (humankind’s) greenhouse gas emissions.

    re 28.

    Scientists can be too cautious in their attempts to not appear like they introduced a bias into their work. As a result, they may introduce a bias into their work in the other direction (like overcompensation).

    I disagree with the comment (in 28.) that “there is significant evidence many academically qualified individuals have allowed their personal beliefs and agendas to influence their evaluation of what the data are saying”.

    I also disagree with the comment (in 28.) that “Being determined to “save the world” certainly risks a loss of objectivity”.

  30. 30
    hank says:

    >save the world

    Oops. CO2 increase accelerating? Coincidence?
    “Through most of the past half-century, levels of the gas rose by an average of 1.3 parts per million a year; in the late 1990s, this figure rose to 1.6 ppm, and again to 2ppm in 2002 and 2003. But unpublished figures for the first 10 months of this year show a rise of 2.2ppm.”

  31. 31
    Eachran Gilmour says:

    I wish I was a scientist who had entered this debate at least 50 years ago.

    It is important that scientists have opinions and have the courage to express them. People who take the trouble to read the literature, at least in outline, know full well what caveats there are and where the lines are drawn.

    So on to plants and more musings of a non-expert : I understand that plants respond differently to different stimuli – when they are stressed they react differently from when they are relaxed and at peace with themselves – please dont laugh you scientists because my brain is not a bad hard drive and I recall that some trees share resources with stressed neighbours under stressful conditions. I would very much like to know the conditions under which the experiments took place. If I were a plant I would “play dead” complete with all the methane output.

  32. 32
    Pat Neuman says:

    re 31.

    I too feel it is important for scientists to study climate, and to express their views on climate change to others. I also believe that hydrologists and meteorologists should be making efforts to account for climate change in meteorology and hydrology, modeling and predictions. My interests are in hydrology, landscaping for wildlife and fossils. Established deep rooted prairie vegetation may survive climate change for awhile, but many flowering plant species need cold seasons to germinate. I’m concerned about the survival of plants and birds. Loss of bird populations would have large effects on potential spreading of vegetation to new areas. Interrelationships between vegetation, birds and insects make for difficult prediction of climate change effects on land species. In trying to go back to the subject of vegetation giving off methane, I think that’s of little consequence to the future global climate in comparison to greenhouse gas emissions and accumulations due to our burning of fossil fuels… mainly just another distraction from doing what we all know we should be doing.. greatly cutting back on our use of energy.

  33. 33
    Mike Carney says:

    J. Wudka’s description of the scientific method:

    “A theory is accepted not based on the prestige or convincing powers of the proponent, but on the results obtained through observations and/or experiments which anyone can reproduce: the results obtained using the scientific method are repeatable.”

    Clearly theories that “can appear in the major journals” get there mostly based upon prestige and convincing powers. As Dr. Kennedy has indicated it is not the journals job to replicate results. So the idea of accepting a theory based upon its being published in a prestigious journal actually runs somewhat counter to the scientific method. In scientific process of conjectures and refutations, publishing is part of the conjecture. Its the beginning not the end.

    Journals provide value by reducing the volume of information to manageable levels. This is good and important but should not be confused with validating the research. Journals could faciliate validation if they required authors to make available all data and methods as a requirement of publishing. Then they could both be the winnowers of the wheat from the chaff as well as instrumental in the validation after publishing. When refutations occur the journals can then proudly point to their contribution to making that refutation possible.

    If your trust still is in major journals then we should look for a major journal on the methods of science that puts publishing in a major journal as the prime requirement for accepting a theory as valid. (Hmmm… bit of a conflict of interest there, oh well).

    “However, the process by which this is decided will demonstrate clearly that the scientific method is alive and well in the climate sciences.”

    This is indeed a noble goal but a success on this theory will not validate others. There are two relatively simple actions that would achieve this noble goal.

    First, transparency, transparency, transparency. Provide all the data and methods so that anyone can replicate the results.

    Second, “If the original claims are not verified the origin of such discrepancies is hunted down and exhaustively studied.” (also from J. Wudka). Errors need to be tracked down and analyzed to improve the process — not to assign blame.

    The goal of trust is so easy to achieve and the task so important.

  34. 34
    JAC says:

    “Am I missing something?

    For their first figure Keppler et al. chose to show methane release rates for leaves previously plucked and air-dried at 25 deg C. They found extremely low rates at 30 degC though the rate doubled every 10 deg C increase up to 70 degC. But how is this data relevant to present day living forests, tropical or temperate, when
    – the experiments used to describe the phenomenon were carried out on damaged (plucked) leaves
    – the lowest temperature for the experiment 30 deg C is at the top end for tropical range forests (18 to 30 deg C), and beyond that of temperate forests (summer monthly T up to 28 deg C)
    – the leaves were from ash and beech, trees more commonly associated with temperate climate

    Without experiments on living trees in present day climatic conditions, I have difficulty in understanding how these findings can provide a sound basis for estimating global methane emissions.

  35. 35
    Eachran Gilmour says:

    Post 34. Quite so!

    Where can I read the original paper please?

  36. 36
    Pianoguy says:

    In a Jan. 17 editorial, the Colorado Springs Gazette used this information to support its traditional “do nothing” policy. The Gazette is behind a firewall, but the editorial has been picked up by at least one other Freedom Communications paper:

    Anyone with the desire to respond can reach the writer, Sean Paige, at:

  37. 37
    Eachran Gilmour says:

    I am probably naive…no I will correct that….I am certainly naive!

    How can the Colarado Springs Gazette possibly print that rubbish? I know that my word, “rubbish”, is not scientific but for goodness sake how many voters read that and how many act on the information?

    What can one do? Isnt it a bit like trying to encourage a little child to believe that 1+1=3. I’m not sure that I have the necessary negatives in place but you must get the drift. I am appalled!

  38. 38
    Coby says:

    I agree that Gazette piece is pretty low on the evolutionary ladder. I did note this line: “German researchers found that trees and plants are responsible for 10 to 30 percent of methane released into the atmosphere annually, according to an article in the journal Nature. That confirms the conclusions of other recent studies on the subject.”

    Is there some basis for this “confirms the conclusions of other recent studies” bit? I thought this Nature paper was pretty much out of left field.

  39. 39
    Terje Petersen says:

    Assuming that the study is correct and living plant produce CH4 then it begs the question what do they make CH4 out of.

    Presumably the Carbon comes from CO2 and the Hydrogen comes from H20.

    So perhaps plants absorb two greenhouse gases (or one gas and one liquid) and emit a third gas.

    By weight CH4 is a more potent greenhouse gas than C02, although the latter obviously achieves more mass with the same amount of carbon. Also H2O is the number one greenhouse gas so it gets really interesting. Although perhaps the H2O is absorbed through the roots as a liquid (seems more likely).

    If CH4 is more pontent than C02 by a factor of 21-23 then how potent is H2O? In other words what is the multiplier for H2O?

  40. 40
    Hank Roberts says:

    > multiplier for H2O?
    Previous discussion is extensive; these might help:

    See also:

  41. 41

    I thought we’ve known for awhile that vegetation and the soil beneath plants make significant amounts of methane. See, for example: Frankenberg et al. Science 308, 1010 (2005) and Ferretti et al. Science 309, 1714 (2005) and I recall another paper within the last year documenting the large amount of methane released from rice paddies. Am I missing something?
    Wes Dingman

    [Response: Those sources of methane come from anaerobic bacteria that thrive in warm, wet conditions. This is (apparently) something directly tied to the vegetation – not bacteria, and thus might be expected to have different responses as a function of climate change etc. The ‘traditional’ sources are still big players, but if this study pans out, this new source will need to be factored in as well. – gavin]

  42. 42
    Harry Eagar says:

    Seems to me Keppler et al’s comment misses the point: Doesn’t this finding call into question the error bars of all the climate models?

    It doesn’t matter whether a source is ‘natural’ or ‘anthropogenic,’ does it, if it’s as big as even the lower estimate here and it wasn’t in the models? At least, if the point is to tease out the anthropogenic component of warming.

    Lynn, go ahead and eat the candy. Buy C&H sugar. Hawaii sugar cane laborers have (by far) the longest life expectancy of any labor category in the U.S.

  43. 43
    Fredrik Lundberg says:

    Re irradiation.
    As far as I know, the only previously known creatures to produce methane are archea, which share many features with bacteria but are not the same thing. For various reasons, not much is known about them. Is there any data on their resilience against gamma-radiation?
    Without such data, why should it be obvious that there is a dose which is certain to kill all the archea, but does not harm the cells of the plant?
    Fredrik Lundberg

  44. 44
    Ernst Beck says:

    Comment on:
    Keppler et al., Methan emissions from terrestrial plants under aerobic conditions, Nature 439, 187-191 (12 January 2006)

    In the above citied letter to Nature the authors concluded out of their experiments: “Here we demonstrate using stable carbon isotopes that methane is readily formed in situ in terrestrial plants under oxic conditions by a hitherto unrecognized process.”
    Reading their paper it is easily seen that their conclusion is not convincing because their experimental strategy lacks and fails some simple tests to exclude or include known biogenic sources of methane.
    At that time common biologic knowledge is: Biogene methanogenesis is performed by archaea, (perhaps some cyanobacteria, fungi and microalgae ) which can be divided into two groups:
    – H2/CO2- and
    – acetate-consumers,
    ( both groups have proteins, carbohydrates or lipds an their derivatives as source).

    Like most organisms plants live ( on surface or interior) together with a lot of specialized micoorganisms (bacteria, fungi) often supporting their metabolism. (e.g. mycorrhiza).To exclude their physiologic possibilities as source of methane generation we have to block their metabolism. To exclude plant as biogenic source of methane we also have to block their metabolism e.g. phytosynthesis.

    1. Keppler et al. choosed gamma ray sterilisation for blocking microbial methanogens. Some archaea are nearly unsensitive to high doses of gamma rays and have the ability to fully regenerate their genome.1 Consequently the experiments showed no significant change of results.

    2. The authors omitted to use methyl fluoride as frequently used to specifically inhibit acetoclastic methanogenesis.2 Adding actate has no influence because inside plant cell there is a sufficient reservoir of sources to reduce to methane.

    3. The authors omitted to incubate plants and parts of it in an CO2 minimum atmosphere ( e.g. <0,01%) to reduce possible methanogenesis out of CO2 by plants and archaea.

    4.Question: Do the authors have used intact plants with intact mycorrhiza or with effectively sterilizised soil for blocking soil bacteria or fungi?

    5. Inside plants there are a lot of anaerobic compartiments for bacteria to live.

    5. Pectin3 or lignin4 are common sources of methane by bacterial methanogenesis.

    My conclusion: experiments done by Keppler et al. gives no conclusion on an new methane source. Possibility of thermophilic methanogensis by archaea is not excluded (see their results of temperature sensitive methane emission).

    Ernst-Georg Beck
    Merian-Schule Freiburg
    Department of Biotechnology and Nutrition Science


    1. e.g. E. Jolivet et al., Physiological Responses of the Hyperthermophilic Archaeon “Pyrococcus abyssi” to DNA Damage Caused by Ionizing Radiation,
    Journal of Bacteriology, July 2003, p. 3958-3961, Vol. 185, No. 13. ( Accessed 2006 Jan 22.)

    2. eg. Holger Penning et al. , Effect of Inhibition of Acetoclastic Methanogenesis on Growth of Archaeal Populations in an Anoxic Model Environment ,
    Applied and Environmental Microbiology, January 2006, p. 178-184, Vol. 72, No. 1, (>. Accessed 2006 Jan 22.)

    3. e.g. Bernard Ollivier et al., Thermophilic methanogenesis from pectin by a mixed defined bacterial culture,
    Current Microbiology Publisher: Springer-Verlag New York ISSN: 0343-8651 (Paper) 1432-0991 (Online) DOI: 10.1007/BF02092877 Issue: Volume 20, Number 2
    Accessed 2006 Jan 22.)

    4. e.g. W. F. Hackett et al., Microbial Decomposition of Synthetic 14C-Labeled Lignins in Nature: Lignin Biodegradation in a Variety of Natural Materials,
    Appl Environ Microbiol. 1977 January; 33(1): 43â??51. ( Accessed 2006 Jan 22.)

  45. 45

    […] From their list these are my favorites: Most puzzling finding from 2006 that has yet to be convincingly replicated: Methane from plants […]