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It’s all about me (thane)!

Filed under: — gavin @ 12 November 2009

Well, it’s not really all about me. But methane has figured strongly in a couple of stories recently and gets an apparently-larger-than-before shout-out in Al Gore’s new book as well. Since a part of the recent discussion is based on a paper I co-authored in Science, it is probably incumbent on me to provide a little context.

First off, these latest results are being strongly misrepresented in certain quarters. It should be obvious, but still bears emphasizing, that redistributing the historic forcings between various short-lived species and CH4 is mainly an accounting exercise and doesn’t impact the absolute effect attributed to CO2 (except for a tiny impact of fossil-derived CH4 on the fossil-derived CO2). The headlines that stated that our work shows a bigger role for CH4 should have made it clear that this is at the expense of other short-lived species, not CO2. Indeed, the attribution of historical forcings to CO2 that we made back in 2006 is basically the same as it is now.

As is well known, methane (CH4) is the greenhouse gas whose anthropogenic increase comes second only to CO2 in its 20th Century effect on climate. It is often stated that methane is ‘roughly 20 times more powerful’ as a greenhouse gas than CO2 and this can refer to one of two (very different) metrics. If you calculate the instantaneous forcing for an equivalent amount of CO2 and CH4 (i.e. for a 1 ppmv increase in both), you find that the global forcing for CH4 is about 23-24 times as large (depending slightly on the background assumed). Separately, if you look up the Global Warming Potential (GWP) of CH4 in IPCC AR4 (the integrated forcing of a kg of CH4 compared to kg of CO2 over a 100 year period), you get a value of about 25. GWP is used to compare the effects of emissions today on climate in the future. The numbers are only coincidentally similar since the GWP incorporates both the weight ratio and the ratio of effective lifetimes in the atmosphere which roughly cancel for a 100 year time-horizon.

In the Second Assessment report (1995), the GWP for methane was 21, and it was increased in AR4 because of a greater appreciation for the indirect effects of methane on atmospheric chemistry, and in particular its role as a tropospheric ozone precursor (since increasing methane leads to an increase in low level ozone). There is also an indirect effect on stratospheric water vapour where methane oxidation is a significant source of water in an otherwise very dry region. Both tropospheric ozone and stratospheric water vapour are effective greenhouse gases so including these indirect effects made the net effect of methane greater.

In the standard ‘forcings bar chart’ such as seen in Hansen’s papers, or in TAR, or AR4 (figure 2.20), each change in atmospheric composition is given a separate column. Thus ozone and aerosol effects are denoted separately. Starting off with a paper we wrote in 2005, though, a different approach that is perhaps more useful to policy makers has also been adopted. This ’emissions-based’ viewpoint attributes the forcings to the actual emissions, rather than to the eventual concentration. Thus since some of the ozone increase is related to CH4 emissions, you get to include that under CH4. The other ozone precursors (carbon monoxide and volatile organic compounds) can also now be blamed for a portion of the ozone impact.

This was incorporated into figure 2.21 in AR4, where it is clear that the impact of methane (once some indirect effects are included) is greater than you would have thought based on the ‘abundance’ viewpoint. Note the changes basically only affect the reactive species. When thinking about the various metrics, the emissions-based view is more closely tied to GWP than the traditional abundance-based approach. A big difference is that GWP is looking forward in time, while emission-based forcings are looking back at historical events.

The increasing sophistication when it comes to attribution and GWP is strongly connected to the development of more comprehensive Earth System Models (ESM) in recent years. These are the descendants of the General Circulation Models of the climate that have been developed over the last 30 years, but that now include interactive atmospheric chemistry, aerosols (natural and anthropogenic) and sometimes full carbon cycles in the ocean and land surface. This extra machinery allows for new kinds of experiments to be done. Traditionally, in a GCM, one would impose atmospheric composition forcings by changing the concentrations of the species in the atmosphere e.g. the CO2 level could be increased, you could add more sulphate, or adjust the ozone in the stratosphere etc. However, with an ESM you can directly input the emissions (of all of the relevant precursors) and then see what ozone levels or aerosol concentrations you end up with. This allows you to ask more policy-relevant questions regarding the net effects of a particular sector’s emissions or the impact of a specific policy on climate forcing and air pollution (see here for a discussion).

Our new Science paper (Shindell et al, 2009) expands on some of the earlier work (as was discussed here) and extended consideration of the indirect effects of CH4 and CO (carbon monoxide) to aerosols as well. This is necessary since SO2 requires oxidants to transform to sulphates (and so is affected by the perturbation of the chemistry by other emissions), and it takes into account the competition between nitrates and sulphates for ammonia (which means that there is a small anti-phasing effect – increasing sulphates tends to decrease nitrates and vice versa). When we did this, we found that methane’s impacts increased even further since increasing methane lowers OH and so slows the formation of sulphate aerosol and, since sulphates are cooling, having less of them is an additional warming effect. This leads to an increase in the historical attribution to methane (by a small amount), but actually makes a much bigger difference to the GWP of methane (which increases to about 33 – though with large error bars).

Currently methane levels are relatively stable (despite small upticks in the last two years) and are running below IPCC projections made in 2001 (this of course is good news). However, CH4 is at more than twice its pre-industrial concentration and so still presents a tempting target for emission reductions which, because of our new work and the relatively short lifetime in the atmosphere, will likely be a little more effective at reducing future forcings than previously thought. Given the value of methane as a fuel, it is likely that more of it will be captured (as in this recent story).

CO2, however, is still increasing dramatically despite the slow down in the economy, and so current growth in radiative forcings is dominated by CO2 and that will very likely continue for decades. Despite our increasing appreciation of the role of other forcings (including land use for instance), the overwhelming driver of climate change in the 21st Century will be CO2 increases.

In a follow-up post, I’ll discuss the sources of methane and the implications of the new results for attribution of climate forcing to different sectors (including agriculture), where there have been some very odd (i.e. wrong) recently published numbers.

191 Responses to “It’s all about me (thane)!”

  1. 151
    Paddy says:

    Geoff, I’m aware who wrote the Livestocks Long Shadow, I’m questioning whether or not it’s valid to include livestock and meat transport emissions and then compare the whole lot to transport emissions.

    I thought Australian landclearing had virtually halted under current laws. I do know there are huge tree plantations happening over there so it must be a net zero by now. The US claims to be a net carbon sequestor with regard to landuse change, and Europe has been mostly cleared for centuries.

    You mean the whole 5 Aluminium mines and 7 smelters in Australia are responsible for the same amount of emissions as 28 million cattle? How did you account for the exported bauxite?

    Beef providing 1.3% of calories seems a bit low, but as a billion odd chinese eat primarily pork and chicken, and most of India’s population worship their cows (india has 20% of the worlds cattle) it may well not be far off. Of course cattle emissions include dairy cows, that “beef” doesn’t. I’ve heard goat meat is the most consumed meat in the world, how it’s emissions compare per kilo of meat would be worth looking up. Can follow link in 144, I didn’t give goat emissions more than a glance, somewhere around 10% of cattle per head from memory.

    144, I wasn’t refering to IPCC, Geoff knew what I was talking about. I did read through the 87 pages to check though. Thanx.

  2. 152
    Paddy says:

    142, well secular A, you’ll have to humour me, it’s mostly cattle I’m refering to, they’re the main animal we associate with methane emissions. Now the US had around 100 million cattle and calves last year and I’ve seen figures estimating Bison numbers from 60-80 million head pre-humans and which number less than a million now. It doesn’t really matter from an emissions view how many are slaughtered each year, it’s the amount that are alive at 2 calves living 6 months each won’t emit more CH4 than 1 living a year. Less probably.
    From IPCC figures Buffalo, which I believe are similar to bison, have similar yearly emissions to cattle.

    You may also note that the higher the quality of food, such as in feedlots, the lower the emissions. Even moreso on a per kilo gained basis. Now I’m no fan of factory farming, nor do I raise livestock, but lets condemn it on a just basis and also remember that cattle usually are feedlotted for only for a few months of their lives. Alebit a short life.

    9 billion is a huge number for sure, I don’t think there is any doubt that people take those deaths for granted and without due respect.

  3. 153
    Brian says:

    Could the explanation for increased tree growth in recent years be, increased levels in CO2 and not temperature. Tests have shown conclusively that plant growth increases when in a high CO2 environment. Panic over.

    [Response: See here. – gavin]

  4. 154
    Barry Day says:

    True!Emissions from 9 billion cattle is a huge and are the main animal we associate with methane emissions.

    Lets get cracking and see if we can double that number seeing we URGENTLY need a “Solar – Grand Minima – Preparedness Plan i.e. Little Ice Age Preparedness Plan”

    James A. Marusek

    Nuclear Physicist & Engineer

    U.S. Department of the Navy, retired

    From the pdf
    “Mankind has been down this road before and we will go down this road again and we will survive.
    The last time we faced this type of disaster was over 300 years ago, as a result it has almost
    been erased from our collective memory.
    A solar “Grand Minima” produces a time of great hardship, a time of significant
    natural global cooling, a time of great famine and starvation and a time of major epidemics.

    The threat from a quiet sun is describe in the Solar Grand Minima Threat Analysis available at:
    This Preparedness Plan is a companion document to this analysis in which the threat is described in substantial detail.
    There are several lessons learned from studying very early global cooling events in Europe.

    * The onset of these conditions can be very abrupt and very severe.
    * A decline in food production due to:
    – Dramatic increase in days with overcast skies.
    – Decline in the intensity of sunlight.
    – Decline by several degrees in global temperature
    – Regions of massive rainfall and flooding
    – Limited regions experienced droughts
    – Shortened growing season
    * A string of major and minor famines
    * Malnutrition lead to weakened immune system. Produced influenza epidemics.
    * Reoccurrence of plagues such as the Black Plague.
    * Lack of feed for livestock
    * Parasites (i.e. fusarium nivale), which thrived under snow cover, devastated crops.
    * Grain storage in cool damp conditions produced fungus (Ergot Blight). Contaminated grains
    when consumed caused an illness (St. Anthony’s Fire) producing convulsions, hallucinations,
    gangrenousrotting of extremities.
    * Flooding created swamplands that became mosquito breeding grounds and introduced tropical
    diseases such as malaria throughout Europe”.

    Lets concentrate on the real problem we are about to face.

  5. 155
    Greg Robie says:

    This thread, by becoming animated (pun intended) about the methane associated with the husbandry of ruminate animals for meat and dairy, dropped consideration of the Arctic as a source of atmospheric methane. The focus ruminate animals is good. This an important source of atmospheric methane that can be addressed by modification of human behavior. To control anthropogenic methane creation, by mitigating/transitioning away from ruminate animals for meat and dairy, is a wedge of the GHG emissions that needs continued redressing. Knowledge, such as has been shared in this thread, is important for doing so intelligently. I would add to that discussionthat just as the developed world, and particularly the US, is addicted to ‘cheap’ oil, the urban/suburban American is addicted to cheap food. Just as vested interests in fossil fuel industries are resisting and manipulating how a price is being put on carbon to protect the profit of their business model, it should be expected that putting a price on agriculture-based methane will be resisted and manipulated. Urban/suburban consumers will be in conflict with rural producers concerning who gets saddled with the costs, and how they are paid for. Fairness will be argued–if differently—by both as a reason the ‘other’ is avoiding responsibility. Just as our government is doing extraordinary interventions to flash-freeze the economic collapse in the hope that such will restart economic ‘growth’ and, thereby, tax revenues to service its deficit spending model of economic growth, government will want to control the CPI—to which many of its unfunded costs are pegged—in its effort to avoid insolvency. Government that is so threatened will be a partial arbiter of competing short-term self-interests in both these matters.

    But, going back to the Arctic and atmospheric methane, there seems to be more we don’t know, than what we do know, concerning the Arctic as a source of methane. For example chw (#123) can link to ‘stable’ average measurements of atmospheric methane at four Arctic measurement stations over the past decade and feel that this confirms Gavin’s assertion that the recent return to increasing atmospheric methane is an “uptick.” The same stability appears to be true of Antarctic station measurements, only those measurements are about 150 ppb lower. At both poles there is a seasonal variation of 60-80 ppb, with the Arctic showing a greater increase in this variability as the past decade has unfolded. Since the air in the atmosphere gets blown around a bit, this use of average figures is likely the least helpful measurement if one is trying to sort out what is happening, rather than wanting to not see a problem; to miss the complexity that a reliance on averages masks. Since methane has a life in the atmosphere of about 10 years, and the Northern Hemisphere seems to ‘pump’ its methane south in a seasonally driven dynamic, and the ~40 ppb rise in the concentration of methane is about half the seasonal variation, together these seem to make a point that is just to opposite of proof that it atmospheric methane is stable in the Arctic, but rather, the ‘uptick” is the “smoking gun” of the methane time bomb has been detonaged.

    Mike Roddy (#8) points out that Kathy Walter’s work has been left out of what was included in this blog post. The report from the British research vessel studies in the summer of 2008 (published this past August) are also not included. Christopher Hogan (#12) points out that the last in-depth coverage of atmospheric methane was in 2005—before the ‘uptick’. Marcus (#42) notes that there is a lot that is not known—an observation that I wold concur with.

    Since I posted my comment #37—reposted below—a person from SEI looked into critiquing it. He told me that he lacked the expertise, and that none of his colleagues were able to provide “insights into the observations” He recommended this reposting. While this thread is getting dated, there is little being covered about Arctic methane. Therefore I hope those who are still looking at this thread, or those who find it via searches on the topic, can critique the following and/or contribute to this thread relative to the Arctic as a source of atmospheric methane.

    lightly edited (for clarity—writing is not a strength) repost of comment #37:

    I would value critique on the following observation concerning the methane “uptick.” When Revkin posted the BP example for capturing methane at gas wells at dotearth 10/22/09-about a gas field going from 4 billion cuft/yr to 10 million cuft/yr.-I realized policies aimed at controlling methane may have been far more successful than the tabling of methane would indicate. That decade long tabling, which the ‘uptick’ relates to, is generally assumed to be due to plugging leaks in gas lines; changes in rice cultivation, and capping landfills. It relates to a measurement of the average level of methane in the atmosphere.

    The BP example may be extreme, but some of the plugs in the former Soviet Union gas lines may have been as dramatic as well. A cursory look at off set projects engaged in under Kyoto suggest a lot of them are landfill capping projects. Given that in Siberia methane was 5 times above background levels in 2003 and in the summer of 2008, up to 100 times greater over areas of the continental shelf in the Arctic, it occurs to me that the mitigation efforts may have masked an ongoing exponential increase in the release of methane in the Arctic.

    The distribution of methane in the atmospheres is strongly weighted to the northern latitudes. In the winter it seems to migrate north, being carried into the Arctic by the same atmospheric condition that gets other pollutants from the temperate latitudes up to the Arctic. With methane having about a 10 year life span (and Lynn #23, I have read that methane first become ethane on its way to becoming CO2 and water), such also suggests that the mitigating policies for CH4 have been more successful than appreciated.

    There is a dearth of scientists studying methane. I heard it reported from Copenhagen this past March that there are only 20 world-wide. Clearly, what funding there is has been focused on studying CO2. To the degree careers follow the money, such may explain both the lack of scientists and funding. The focus on CO2 would also explain why the renewed increase in CH4 might be labeled only an uptick.

    As I consider the changes in climate occurring in the Arctic, a factor I can see in play among all the others-and feeding all the others-is the overlooked ongoing methane increase. Are there any huge oversights in this analysis? If not, could it be further critiqued so we don’t continue to miss it?

  6. 156
    JCH says:

    There are not 9 billion cattle. The US has around 96 million beef animals – cow-calf operations -, and around 20 million dairy cows. The world population of cattle is around 1.3 billion. There are roughly 65 million hogs in the United States – not counting the ones with extended forks. Of course, the US also imports a great deal of meat, so some of theirs is really ours, too.

    The 9 billion slaughtered for consumption in the United States is mostly poultry – not meaning to diminish the life of a chicken.

  7. 157
    Richard Schwartz says:

    Re # 50–There are several effects that may have implications for the apparent leveling off of the temperature in the 2001-2009 period. First, it seems to have been established that the solar forcing has undergone a small decrease on average, but this alone probably cannot cancel out the expected effect of the greenhouse warming. A second aspect is that much of this period was dominated by the natural La Nina pattern which tends to produce cooler temperatures, at least on regional scales. A third aspect is the industrialization of China and increase of particulate emissions, the residue of which has been reported in the Western U.S. snowpack. These emissions could well be having some impact by decreasing the solar flux reaching the earth’s surface.

  8. 158
    Hank Roberts says:

    Some numbers:

    Methane released from enteric fermentation
    Assessment per region and livestock production system
    Resulting total of 86 million tons CH4 per year

    Methane released from animal manure
    Assessment per region and livestock production system, using updated emissions factors
    Resulting total of 18 million tons CH4 per year

    Resulting Overall Contribution
    About 2.2 billion tons CO2 equivalent:
    37% of total anthropogenic CH4 emissions

  9. 159
    Greg Robie says:

    Paddy (#152), this study$foragebeef/frgebeef.nsf/e5ae854df3230ce787256a3300724e1d/30242e114ec84f8487257162006b48b0/$FILE/GHGforagediets.pdf indicates just the opposite of what you have stated. It says, if I’ve read it correctly, that a lower quality diet produces 46% less methane, but no difference in methane generation from the manure pack (but the lower quality feed produces less manure). This study, in feedlot conditions, suggests that, depending on how much quicker the force feeding of a high protein diet is for finishing a beef creature to marketable size, feedlot operations create more methane. The difference would be influenced by pasture management/conditions and weather factors. In this study, , such resulted in .2 kg/day lower growth rates but greater profitability for the farmer (two other studies are referenced in this report with .47 and a .45 kg/day differences in weight gain during finishing. Regardless, the manure pack is a feedlot phenomena. The anaerobic decomposition occurring in the pack would not occur on the range.

    When fossil carbon footprint costs are factored in for growing and transporting the grain for the feedlot model, in addition to methane production, the feedlot business model is in trouble. Add in the carbon sequestering that free range cattle help the soil pull off and pasture feed remnants gain points. Back out federal subsidies for grain production (that help keep the CPI low) and isn’t the feedlot business model an economic joke AND a GHG production amplifier?

  10. 160
    JCH says:

    Greg, I’m just a cowboy, but that study is comparing two formulated diets in a feedlot. You will note that the high forage diet includes a significant sunflower seed portion. Out on the range, the only way cows could get sunflower seeds would be to stage a break out and walk to the nearest convenience store. It’s possible to supplement a range diet, but to do it to the extent in that study – I suspect it would be very expensive and problematic. It takes a lot of CO2 to put sunflower seeds into a pasture.

    I think it is pretty well established that a standard pastoral diet produces more methane than a customized diet. I read a study on caribou, and their methane production went way up in the winter when they had to start eating woody plant material. I would not be surprised if the same were not true of cattle. As the food quality of the pasture diminishes, methane may go way up.

  11. 161
    JCH says:

    Greg, the tests I’ve read about – out on the range – may not demonstrate that to the extent it appears. The pies dry out, and that is when the tests stop. That’s when we started throwing them at each other. Then you get precipitation. What happens then? Also, if you supplement their range diets with minerals and feed designed to reduce methane, they congregate around that feeding station and you get a pretty deep pile in no time, which they keep wet with urine.

  12. 162
    Greg Robie says:

    JCH, cowboys, due to being out in naturally complex systems (as opposed to climate controlled, artificially lighted ivory towers) can, by mirroring their environment, know more; can think more complexly. Consequently, I would trust the reasoned thinking of the cowhand’s seat of the pants understanding over an academic’s hypothesis in the application of Occam’s razor—though an academic, having more ‘enlightened’ hours in the day, might read more; read better.

    I didn’t see the point you’ve made about sunflower seed. I did see that it was a short study—and feedlot-centric. The second study I linked to was an attempt to quantify how much longer a pasture finished animal might take to reach slaughter-ready condition in terms of methane production and decrease the 46% ‘savings’ a diet of ruffage might have. The range, a .2 – .47 kg/day difference during finishing does eat into the ‘savings.’ I remember reading somewhere that a steer can be raised to slaughter-ready size in 18 months today vs 5 years a couple of generations ago. That time difference makes feedlot operations a methane mitigation winner—if eating such meat is a diet that must be preserved while trying to preserve the planet as a habitable place for humanity.

    In terms of thinking about what makes rational sense in sorting out that question, once you eliminate the feedlot’s ‘ivory tower’ control for pasture, latitude, soil, and weather variables, any resulting report can have enough “it depends” that the writing itself needs “Depends.” Anyway, the point you make has a salt-of-the-earth integrity I respect. If we are serious about controlling anthropogenic methane, ruminant animals husbandry has to go; as does your employment.

    The fun of cow pie fights may be lost on academics, and is generally limited to a child-like male sense of humor and delight. With the elimination of cowboys, it may become a lost art-form within the parameters of the entertainment industry. Virtual dry turds just don’t pack the same emotional punch as the real thing.

    That aside, if they didn’t get tossed around, they could be studied. I bet such studies would show that they, like pot hole wetlands in the plains, are micro environments for earth building microbes and bugs, that, in terms of sequestering carbon, dung pies play as vital a systemic role. And, particularly given the life times of the greenhouse gases of CH4 and CO2, may more than compensate for the methane produced. Regardless, the annual rainfall will be a variable that will have simple minded thinkers calling for diapers when trying to make sense of any report. Conversely, If one grew up in a hut plastered with dung straw, and urine, one would know that once dry, it sheds water quite well. Add this to the point that additional methane production from dung remains stable becasue the conditions for anaerobic decomposition ends with the initial drying (and the death of the related microbes excreted with the manure).

    BTW, can you venture a hayseed assessment of my comment #155 about Arctic atmospheric methane? If the methane time bomb has been detonated, such makes this conversation about ruminants and methane mitigation, rather academic . . . kind of like the argument that geopolitically jurisdictional limits, cap & trade ‘controls’, and offsets are a scientifically relevant approach to mitigating fossil carbon generation!

  13. 163
    Paddy says:

    159, I’ll stick by my guns- high quality food produces less CH4.
    I think you will find that feedlots are situated close to feed sources, even with energy prices as cheap as they are transportation is costly.

    Hank, some numbers: livestock- 2.2 billion tonnes CO2e
    Fossil fuel CO2- 28.4 billion tonnes CO2

    New carbon to biosphere each year- Livestock Nil*
    fossil fuels- 8 billion tonnes(my back of envelope figuring)

    *Accordingly agriculture as a whole is said to be responsible for consuming 1.5% of fossil fuel derived energy, and obviously livestock production does use a fraction of that.

  14. 164
    Hank Roberts says:
    Each green circle is a large feedlot.
    There are other feedlot problems turning up:
    which are going to be of interest to the researchers working on long distance dust movement generally

  15. 165
    dhogaza says:

    I think you will find that feedlots are situated close to feed sources, even with energy prices as cheap as they are transportation is costly.

    On the other hand, many of the cow-calf operations that provide the steers are often in the semi-arid west, places like se oregon, nevada, new mexico, etc. They haven’t walked to the feedlots since before clint eastwood starred in “Rawhide” …

  16. 166
    nathan currier says:

    Since you’re on the topic of the indirect aspects of the methane GWP, could you explain how to calculate in the FF (feedback factor).

    I’m trying and can’t figure out how to add it in.

    Without indirect effects, I get the CH4 GWPs – 49.54 ;17.75; 5.43 (20,100,500 yr horizons respectively)

    When I add the O3 & H2O indirect effects according to AR4 updated figures
    (25% + 15%), then I get GWPs of – 69.35;24.85;7.61.

    I’m assuming my 20 and 100 year horizons still don’t quite match the updated IPCC ones because the FF isn’t in there. Is that right?

    Could you show me how to calculate that myself? I’ve read discussions on
    what is behind it, the adjustment time changes, etc., but that doesn’t help me to calculate myself…..

    Thanks SO MUCH!!!

  17. 167
    Greg Robie says:

    Hello Gun Totten Paddy,

    Having read Chapter 5, it looks to me like it is saying that all that is needed to bring the CH4 production of a low protein diet ruminates in line with feedlot cousins is to add a bit of a molasses-urine milkshake to the diet. What I do not see in that chapter is a comparison of CH4 production of feed lots and well managed pasture. Perhaps all this thread has identified is more of the “it depends” variables about which too little is know and requires positions to be defended with fire-power rather than fact-power.

    BTW, what is your take on the thoughts about Arctic methane as per comment #155?

  18. 168
    Paddy says:

    164, Hank I think you’ll find plenty of worries about environmental estrogen levels originating from human sewerage.

    Seen an aerial view of a city waste water plant let alone the concrete monstrosity that is the modern city? makes a feedlot look teensy weensy. The green dots can be a bit misleading, there are 45 million acres in Nebraska, and at normal feedlot densities 20000 acres would be cattle pens. 0.0005%.

    165, So it’s cheaper to use unsustainable fossil fuels to transport cattle by truck rather than walking? There’s a surprise. Walked to work lately? The average American commute is 16 miles.

    167, I’ll go back through chapter 5 when I get a chance. There’s no doubt that the variables are diverse, and depends too on how we choose to measure impact- emissions per head, per kilo gain etc. Even between grass species methane produced can vary up to 50% per head.

    Re.155, it’s a wee bit longer than my attention span but here goes:
    Addressing Arctic methane, theres anticipation than extra temperature will release methane from melting permafrost and lakes. I too have read about the levels being well above background, but I don’t know if this is a recent comparison or if levels would have been similarly elevated pre-fossil fuels. My understanding is methane releases from permafrost will be limited through microbial conversion. Lakes I’m not so familiar with. The amounts of methane stored are staggering.

    My parting thoughts on livestock methane:
    We could well eradicate ruminants and get a one off fall in methane levels, lets say for convienience take 20% off 1750ppb to be 1400ppb(simplistically livestock contibute 40% of total humane methane emissions, which is roughly the same as natural methane emissions.thus 20% of all methane emissions).

    A one off 350 ppb fall in CH4 compared to an annual gain of 2000ppb of CO2. Probably looks alright on paper using 23x warming potential, but factor in the weight difference per molcule of CH4(approx 1/3 of CO2) and we’ll find that one years CO2 production from fossil fuel burning eliminates all the gain of such an action.

    some assumptions I’ve made-
    3000 Gt of CO2 in atmosphere
    28 Gt of Antropogenic CO2 emissions annually
    CO2 380,000ppb
    CH4 1,750ppb for ease of calculation
    CO2 molecule 2.75 times heavier than CH4 molecule
    GWP of gases compared by weight

  19. 169
    Greg Robie says:

    Paddu, thanks for your thoughts regarding the increase in Arctic CH4. Since you frame your reply around such as an _anticipated_ increase, I guess I was not clear. I observe that the ‘anticipated’ increase is a present reality—but for enough knowledge and data to see this; but for a focus on CO2. The amounts of CH4 in the Arctic are staggering. And the ship-based 2008 measurements in the Arctic Ocean over the continental shelf turned up up-to-100X higher levels of CH4 over previous background measurement data (clathrates are another source of CH4 in the Arctic, besides soils and lakes—both microbe-driven sources).

  20. 170
    sciencebod says:


    I’m new here. I do an Energy Blog for the Daily Telegraph, and am seeking an urgent answer to a question that’s been bugging me and others. Can anyone help?

    It’s to do with the mechanism by which infrared-irradiated CO2 gas dissipates energy. Is it by re-emitting a quantum of ir light? Or do the energised molecules, with their enhanced bond-bending vibration collide with other molecules, including non-greenhouse gases – giving them extra kinetic energy.In other words, bending vibration to translational motion. In the latter case, the resulting rise in temperature would presumably be radiated as a continuous spectrum from a blackbody.

    I’m still encountering people who say that there is no real physics to support the notion of a greenhouse gas radiating energy back to Earth, and I have to say I’m experiencing great difficulty in tracking down any references despite an hour or more of googling. It does seem to be a defect of the theory if the mechanism as to how ir is radiated back to Earth is not common knowledge and/or shrouded in mystery.

  21. 171
    David B. Benson says:

    sciencebod (170) — It is actually not so easy. In the links, BPL provides some (approximate) equations:

    A different approach may be found in Ray Pierrehumbert’s

    If that is not enough then I fear you may need a graduate text on atmospheric physics, not something I care to tackle…

  22. 172
    sciencebod says:

    That’s fine to be getting on with, David. Thanks a lot. I’ll get back once I’ve seen what those sites have to offer.

    Just a brief thought. Could one not go out after sunset, with no moon, and monitor back-reflected infrared. If it matches the discrete lines in the emission spectra of greenhouse gases then it’s a photon in-photon out mechanism. But if it’s a continuous spectrum, as if from a blackbody, then it’s a photon in, no immediate photon out. The incoming photon has briefly energised the greenhouse gas molecule, which has then shed the energy through kinetics, ie imparting translational kinetic energy to its neighbours, which then radiate a bit more as a blackbody. So there is a photon out, finally, but not from the originally energised trapping molecule, or even from a greenhouse gas (predominating O2 and N2 would serve for the purpose of dissipating the excited bond enrgy. I hope that makes sense.

  23. 173
    paddy says:

    grog, 100x can be somewhat misleading, if you measure near a methane plume then yes it is likely to have a higher conc than background.
    The same study indicates surface methane at 3 to 4 times background, which is alarming to a degree but we have to accept that some areas emit and some don’t. Those that emit would presumably have a higher local conc.
    The gist of my point is that I haven’t found what the continental emissions are now compared with 20 or so years ago, and whether or not they are orders of magnitude different. Some direction would be welcome.

  24. 174
  25. 175
    Hank Roberts says:

    > monitor back-reflected infrared. If it matches the
    > discrete lines in the emission spectra of greenhouse
    > gases then it’s a photon in-photon out mechanism. But
    > if it’s a continuous spectrum, as if from a blackbody,
    > then it’s a photon in, no immediate photon out.

    Remember the infrared going out from the ground is already very broad. Most of it gets captured, except for a few narrow ‘windows’ — so you’re not looking for what you think, I think.

    I think there will still be emissions characteristic of the various bonds in the molecules — that’s one way gases are identified, by their emission spectrum fingerprints. Someone who knows something can certainly comment on that.

    But if we got only exact lines, the infrared astronomers would not have to make so much of an effort to subtract the atmospheric background, as by tipping and tilting telescopes to subtract the atmospheric emission; they could just filter the narrow spike frequencies.

  26. 176
    sciencebod says:

    Thanks Hank

    Yes, the outgoing ir radiation is ‘broadband’, so to speak (is one allowed to say that without causing confusion)? But it’s possible to imagine that an ir spectrometer pointed up at the sky after sunset might pick up nothing but discrete lines were all the back-radiation due to absorption and re-emission at those fixed ir frequencies that correspond with specific modes of bond excitation. Alternatively, back radiation could also be broadband if the bond-exciation were quickly dissipated to neighbouring molecules via collisions, the latter acquiring greater speed, and becoming better blackbody broadband radiators.

    Yes, the difficulty is that there will always be a warm blanket of gas with broadband radiation coming back to Earth. But the key question is whether there is additional energy at discrete frequencies, and measuring the amountproportion of energy coming back in discrete frequencies. What would it be as a percentage of the flux of blackbody ir radiated from the planet’s surface?

    A lot of sites and papers seem to imply that discrete frequencies are simply pinged back to Earth, but I doubt very much that is the case. It’s probably mainly “broadband” due to kinetics and momentum-transfer, but I wish I had hard evidence on that.

    Thanks again. Further comments welcome.

  27. 177
    Jamie Lloyd says:

    After reading most of these blogs, I have a Question: How do we rationalize the two sets of data below in a way that makes sense to average people? Al Gore just putting the new Shindell et al numbers out there without cogent explanation really confuses people and undermines support at a pretty crucial time, politically.

    Please help.

    IPCC (2007 Synthesis Report) says:
    Global Anthropogenic Greenhouse Gas Emissions in 2004
    CO2 (total:fossil, cement, deforest) = 76.7%
    CH4 = 14.3%
    N2O =7.9%
    F-Gases = 1.1%

    Al Gore’s new book says:
    Six Types of Global Warming Pollution
    CO2 = 43.1%
    CH4 = 26.7%
    Black Carbon = 11.9%
    Halocarbons = 7.8%
    CO + Other Organic Compounds = 6.7%
    N2O = 3.8%

    [Response: The principle difference is whether you attribute the forcing by what we emit or by what is in the atmosphere. They differ because of the indirect effects (mainly due to methane) on atmospheric chemistry. Our previous post on methane has some links and background. Also check out figure 2.21 in AR4. – gavin]

  28. 178
    Completely Fed Up says:

    If 100% of IR at CO2/H2O/etc bands are absorbed, then the emission spectra of the earth would be broadband at ~220K (or whatever) with ABSOLUTE BLACK at those absorption bands.

    If this isn’t true then it can’t be 100% absorbed, can it? Since only with less than 100% absorption can any of that absorbed light be visible from space.

    If you maintain 100% absorption therefore no effect from more CO2 yet also agree with the evidence that these absorption lines are not black when earth is viewed from space, please explain the physics.

  29. 179
    Hank Roberts says:

    > imagine that an ir spectrometer pointed up at the sky after sunset might pick up …discrete lines

    You’re pointing out that the words used in verbal explanations often aren’t clear, I think. Yep.
    And the infrared astronomers do look up, and do not see discrete lines (else they could filter them out and work from the grouhnd). So you do have your experimental proof, if that’ll do.

    This has been gone over at RC in several earlier topics. It took not just math but serious work with big computers to figure it (per Spencer Weart’s book); for the rest of us words like “mean free path” and “relaxation time” and “time between collisions” and altitude and density are just poetry.

  30. 180
    sciencebod says:

    I think we’re on the same wavelength, Hank (no pun intended). If I read you correctly – let me know if that’s not the case – then the back-radiated ir is broadband – it’s been monitored and there’s no evidence of discrete wavelenghts. Therefore its wrong to imagine that CO2 moleclules etc act as a miniature trampolines for receiving and bouncing off ir photons, where a photon is briefly absorbed and immediately re-emitted at the same or similar discrete wavelength, which finally returns to Earth, still as discrete wavelngths. If by “poetry” your mean that the literature you read is full of terms like mean free path etc, then you do seem to be suggesting that it’s a chain of events that returns ir to earth as broadband radiation. In other words: CO2 molecules absorbs ir photon, becomes energised eg bond-bending oscillation, the oscillation energy is then passed on to another molecule, not necessarily greenhouse gas – through random collision and becomes, say, translational energy by transfer of momentum (note the original CO2 has retained its ir photon – it has not re-emitted). The “lost” photon finally reappears as part of the broadband spectrum of a slightly warmed troposphere that has captured and dissipated the energy of ir radiated from Earth. In other words, narrow band ir out, broadband back. Sorry if I’m stating the obvious, but it’s been difficult to get a clear statement of step-by-step sequences of events, yet one still gets sniped at whether one says it’s a simple ping-back mechanism or the opposite where the specific ir frequencies are lost, and the troposphere just becomes a warmer blackbody radiator.

    Completely Fed Up – thanks for the interest. We may or may not be talking about the same thing. It always takes me a while to get on to the same wavelength with a fresh contact. Would you agree or disagree with the mechanism set out here?

  31. 181
    sciencebod says:

    Oops.I made a silly slip in that last comment. I said “narrow band ir out”. That should have been broadband out, needless to say, with selective removal of discrete wavelengths on first encounter with CO2 etc. Sorry about that. It’s late where I am.

  32. 182
    Syafrin says:

    I am just an ordinary guy with no atmospheric science knowledge, I have a question bugging me long enough. Can anybody please help answer this question:
    Given all the present day figures and parameters of the global warming science, including the delay of terrestrial and ocean heat process, how much time we have before the arctic completely melts away and the peatbogs give out all the methane? I am aware of Wieslaw Maslowski’s prediction as well as Jay Zwally. Will the Arctic methane in the atmosphere suffice in invoking the methane clathrate out of the continental shelves?

    Two days ago I stumbled on a calculation which I can’t understand at:


  33. 183
    Completely Fed Up says:

    sciencebod: “through random collision and becomes,”

    INELASTIC collision.

    That is the extremely important point that EVERY SINGLE DENIER ignores.

    Rather like they ignore the second law of thermodynamics says NET energy flows from hotter to cooler bodies. Forgetting “NET” and just coming to the assinine conclusion that a cooler atmosphere cannot warm the warmer ground. Assinine because NET flows are away from the warmer earth, but that is less than the NET flow if there were no atmosphere. The difference being the flow of energy from the cool ***but not absolutely cold (Zero Kelvin)*** atmosphere to the ground. For denialists, it’s as if there can be NO RADIATION OF WARMTH from a layer that is cooler than an adjacent one.

    “In other words, narrow band ir out, broadband back”.

    You’re looking for the term “thermalisation”. With enough collisions and transformations, all that energy is turned into a thermal broadband emission.

    Remember: there is no such thing as narrow band ir, just a narrow range of IR photons in the system. If those photons are destroyed by absorption, they don’t exist any more. How that energy is expressed depends on the system they are in, not the original source.

    And in the case of the optically thick atmosphere (in wavelengths it IS optically thick), the body they are in is a thermal source and will radiate as such with black-body intensities.

  34. 184
    paddy says:

    thanks hank, I too always go to a pro-vegetarian site when I want objective information on animal production.

    Relating chicken production to a methane post is a bit off track though, chickens have one of the most efficient food conversion ratios of any land animal and aren’t enteric fermentors.

  35. 185
    sciencebod says:

    Hello CFU

    It’ll take me a while to get my mind round all the subtleties there. One thing on which I think we’re both agreed is that the Second Law is only about initial and final states, and does not attempt to prohibit radiation exchanges that are from cooler to warmer bodies. A radiating mass of greenhouse gas will send out energy in all directions – some into space, some back to Earth. It has no way of knowing what is hotter or cooler – and doesn’t care anyway.

    The only difference that I can see in having a blanket of greenhouse gas is that it creates higher steady state temperatures on Earth than would otherwise be the case, with an intermediate temperature in the blanket.

    But some people are not happy with an argument that says Earth would be cooler but for the blanket – despite their guru acknowledging as much on p.366 of the Holy Writ. One cannot take the blanket away to give them proof. Thus my interest in knowing if it were possible to provide more direct evidence of back-radiation of infrared. If it were “broadband” then that would would prove nothing. But if it were narrowband, ie with frequencies corresponding to the known emission spectra of greenhouse gas molecules, then it would be exceedingly hard for them to deny the greenhouse gas effect would it not?

    One would presumably have to do the demo at night. During the day, the same greenhouse ags molecules would be absorbing photons from the sun’s ir radiation, creating an absorption spectrum, with “gaps” at the critical frequencies that would make it harder to distinguish emission from the atmosphere at those same frequencies.

    Thanks again for the interest.

  36. 186
    Pete says:

    Hi, Gavin. Could you comment further on this exchange from an older post? Why is it much better to burn methane than to release it? Thanks!

    >>Question: Up here in Alaska our own Katey Walter is talking about the tundra methane releases as a source of energy for nearby communities. Understanding that nobody is going to build giant capture devices, still I would think burning methane would result in less damaging gases. Any calculations on that?

    [Response: Definitely. Methane is much better off burnt than released. (say hi to Katey if you see her). – gavin]<<

    [Response: Because molecule per molecule CH4 is a much more powerful GHG than CO2. So if you burn the gas, CH4+2O2 => CO2 +2H2O you reduce the forcing (and hopefully you get to use the energy released for something useful). – gavin]

  37. 187
    Pete says:

    Much appreciated.

    Does the time frame matter though? I understand the higher short-term forcing, but on a century or longer scale would the additional CO2 eventually catch up in terms of its impact because of its longer residency in the atmosphere? Does the GWP of 33 for methane over 100 years make this a simple answer of “no.” Also, any idea on how completely methane combusts? Would there still be a fair amount of methane released even if you burnt it?

    If you use the combustion for energy than it makes this a moot point, but I’m curious about the comparison if you don’t.

    Thanks, and thank you very much for the resource you guys provide.

  38. 188
    Completely Fed Up says:

    sciencebod: ” Thus my interest in knowing if it were possible to provide more direct evidence of back-radiation of infrared.”

    There are pictures of the brightness of the earth from space that shows at absorption bands for CO2, the earth is getting dimmer.

    If that’s not enough, then until we genetically engineer humans to see photons in transit ***in the transverse direction of travel*** and ***individually*** and also to get them to look (which for most denialists will be harder than the genetic engineering), there’s no way.

    Just like you can’t prove to the extremely devout that there is no God.

  39. 189
    JBL says:

    Pete: if methane gets into the atmosphere, at some point it breaks down into CO2, so you get the effect from the methane followed by the (longer-term but less powerful) effect from CO2. If you burn the methane directly, you cut out the methane part of that deal completely and leave the CO2 part unchanged. Thus, it’s strictly better to burn the methane directly (even if for no useful purpose) than it is to release it into the air.

  40. 190
    Marcus says:

    Pete (#187):
    1) The “GWP” is supposed to take into account time frame (well, at least for 100 years): using a GWP, methane is still 25 or so times as potent a GHG as CO2 (integrated radiative forcing).

    2) The other key point is that if you don’t burn methane at the release, it still eventually oxidizes to CO2 in the atmosphere (sometimes producing ozone and reducing hydroxyl radical along the way): so really what you’re doing by burning it is not “producing” CO2 but rather skipping the 10 year stage in which the methane hangs around as CH4 before turning into CO2 anyway.


  41. 191
    Pete says:

    Thanks everyone (Gavin, JBL, and Marcus).