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How much does animal agriculture and eating meat contribute to global warming?

Posted on 30 November 2015 by dana1981

This is the new rebuttal to the myth 'animal agriculture and eating meat are the biggest causes of global warming.'  It's available at the short URL

The burning of fossil fuels for energy and animal agriculture are two of the biggest contributors to global warming, along with deforestation.  Globally, fossil fuel-based energy is responsible for about 60% of human greenhouse gas emissions, with deforestation at about 18%, and animal agriculture between 14% and 18% (estimates from the World Resources InstituteUN Food and Agriculture Organization, and Pitesky et al. 2009).

WRI global GHG emissions flowchart

Global human greenhouse gas emissions flowchart, from the World Resources Institute.

So, animal agriculture and meat consumption are significant contributors to global warming, but far less so than fossil fuel combustion.  Moreover, fossil fuels are an even bigger contributor to the problem in developed countries, which use more energy and have increased livestock production efficiency (Pitesky et al. 2009).  For example, in the United States, fossil fuel-based energy is responsible for about 80% of total greenhouse gasemissions as compared to about 6% from animal agriculture (estimates from the World Resources Institute and Pitesky et al. 2009).

US GHG emissions flowchart

US human greenhouse gas emissions flowchart, from the World Resources Institute.

How does animal agriculture cause global warming?

On of the main ways in which the livestock sector contributes to global warming is throughdeforestation caused by expansion of pasture land and arable land used to grow feedcrops.  Overall, animal agriculture is responsible for about 9% of human-caused carbon dioxideemissions globally (UN FAO).

Animal agriculture is also a significant source of other greenhouse gases.  For example, ruminant animals like cattle produce methane, which is a greenhouse gas about 20 times more potent than carbon dioxide.  The livestock sector is responsible for about 37% of human-caused methane emissions, and about 65% of human nitrous oxide emissions (mainly from manure), globally (UN FAO).

Beef is a bigger problem than other sources of meat

Producing beef requires significantly more resources (e.g. land, fertilizer, and water) than other sources of meat.  As ruminant animals, cattle also produce methane that othersources (e.g. pigs and chickens) don't.

Eschel et al. 2014 estimated that producing beef requires 28 times more land, 6 times more fertilizer and 11 times more water than producing pork or chicken.  As a result, the study estimated that producing beef releases 4 times more greenhouse gases than a calorie-equivalent amount of pork, and 5 times as much as an equivalent amount of poultry.

Eating vegetables produces lower greenhouse gas emissions yet.  For example, potatoes, rice, and broccoli produce approximately 3–5 times lower emissions than an equivalent mass of poultry and pork (Environmental Working Group 2011).  The reason is simple – it's more efficient to grow a crop and eat it than to grow a crop, feed it to an animal as it builds up muscle mass, then eat the animal.

Environmental Working Group GHG Lifecycle Assessment of foods


Greenhouse gas lifecycle assessment for common proteins and vegetables (EWG 2011).

How do the numbers get misrepresented?

There are often suggestions that going vegan is the most important step people can take to solve the global warming problem.  While reducing meat consumption (particularly beef and lamb) reduces greenhouse gas emissions, this claim is an exaggeration.

An oft-used comparison is that globally, animal agriculture is responsible for a larger proportion of human-caused greenhouse gas emissions (14-18%) than transportation (13.5%).  While this is true, transportation is just one of the many sources of human fossil fuel combustion.  Electricity and heat generation account for about 25% of global humangreenhouse gas emissions alone.

Moreover, in developed countries where the 'veganism will solve the problem' argument is most frequently made, animal agriculture is responsible for an even smaller share of the global warming problem than fossil fuels.  For example, in the USA, fossil fuels are responsible for over 10 times more human-caused greenhouse gas emissions than animal agriculture.

That's not to minimize the significant global warming impact of animal agriculture (as well as its other adverse environmental impacts), especially from beef and lamb, but it's also important not to exaggerate its contribution or minimize the much larger contribution of fossil fuels.

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Comments 1 to 50 out of 174:

  1. Excellent post.

    The flow charts are a fantastic visualization of the ratios for various energy uses and related emissions. This really points to the core targets that Americans can work on for overall emissions reductions, and where they can make the biggest impacts.

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  2. Given that methane in the atmosphere breaks down to carbon dioxide and water (CH4 + 2O2 -> CO2 + 2H2O) fairly quickly, shouldn't increased methane levels be considered as increased CO2 levels for longer term planning?

    Basically, it seems to me like that whole '20 times more potent' bit on methane may inflate it's relative importance. Yes, in the short term one molecule of methane may be 'as bad' as 20 molecules of CO2... but the short term impacts are miniscule. In the long term that one molecule of methane is going to be one molecule of CO2... and thus methane emissions are, for practical purposes, equivalent to CO2 emissions.

    Put another way... should the 14% global GHG impact from methane be viewed as a short term mathematical construct, with the actual long term impact actually more like 0.7% (14% / 20) once that methane becomes CO2?

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  3. Thanks for putting this in perspective, Dana.

    I think that the point of focussing in on beef and dairy is not so much that we can solve the climate crisis this way, but that avoiding beef or just cutting down is something that everyone can do that will make a small difference to emissions, a significant improvement to personal health and a reduced impact on the land.

    I should admit at this point that I am a non-observant vegetarian.

    XKCD has a cartoon that nicely illustrates the disproportionate mass of the world's cattle, with the implication that they have an outsize ecological hoofprint. George Monbiot also has a recent article on what species is causing the biggest contribution to the population crisis.

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  4. CBDunkerson @2, here is the CH4 cycle as estimated in AR5:

    The important factors are the annual increase (17 Tg CH4/yr) and the cumulative increase (2970 Tg CH4/yr).  As each molecule of methane (atomic weight 16) gets converted to a molecule of CO2 (atomic weight 44), these need to be multiplied by 2.75 to get the decay emission at Tg CO2, or by 0.75 for Tg C.  To convert to Petagrams, we need to multiply by 0.00275 and 0.00075 respectively, giving a cumulative emissions after decay of 2.2275 PgC, and 0.01275 PgC/yr.

    For comparison, here is the CO2 cycle from AR5:

    The cumulative emissions after conversion amounts to 0.9% of CO2 emissions, and is well within error.  The annual emissions amount to 0.3% of annual CO2 emissions and again is well within error. 

    The upshot is that methane can in fact be ignored for longer term planning (>200 years).  Its decay time of 12.4 years, however, means it will take approximately 50 years to effectively remove the excess CH4 with no further emissions, meaning it is a very substantial player over the coming century.

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  5. I'm wondering about the country-by-country comparison. Specifically, when the claim is made that "in the USA, fossil fuels are responsible for over 10 times more human-caused greenhouse gas emissions than animal agriculture," does that include all the cattle that are imported from other countries where forests are being destroyed to support them?

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  6. (About 10 million pounds of beef from Brazil per month, for example.)

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  7. Your greenhouse gases for foods chart is grossly misleading since it lists by weight instead of by calorie and protein content.  

    For instance, one pound of dry beans contains five times as much protein and calories as tofu and costs much less, yet your graph makes them equals in global warming gases. Milk and yogurt have many fewer calories per pound and grams of protein per pound than nuts. Fat free, sugar free yogurt has only 200 calories per pound while nuts come in at roughly 1900 calorie. Thus, on a per calorie basis, yogurt is ten times more polluting than nuts and seven times world than rice or beans/lentils. That's huge.

    Many vegetables don't do well on a per calorie basis, but to have some health benefits, while beef and pork definitely do not. Canned foods also have a much higher footprint due to the canning, so dry beans are several times less polluting than canned and, of course, have no BPA. Medical care has a carbon footprint, too.

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  8. TomR - this 2014 study attempted to estimate GHG emissions of various diets, standardized to 2000kcal/day. Their conclusion was that meat-eaters produced about twice as much GHG as vegan diets.

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  9. Another thing that this piece overlooks is the degree to which people can alter their ghg emissions of one sort or another. Many people are stuck with, say, long commutes to work, required trips to conferences, appartments where they can't completely control the heat...

    But diet is something that pretty much everyone has some ability to control by themselves. If it is one or one of the few things someone has control over, then it doesn't really matter how it stacks up against other contributors. If you can't change those, but can change your diet, everyone who can should be encouraged to do so.

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    @2 C B Dunkerson, Regarding the futility of mitigating short lived Greenhouse Gases like CH4:

    "A re-examination of the issues shows that the benefits of early SLCP mitigation have been greatly exaggerated, largely because of inadequacies in the methodologies used to compare the climate effects of short-lived substances with those of CO2, which causes nearly irreversible climate change persisting millennia after emissions cease. Eventual mitigation of SLCP can make a useful contribution to climate protection, but there is little to be gained by implementing SLCP mitigation before (my emphasis) stringent carbon dioxide controls are in place and have caused annual emissions to approach zero." the quote is from Short-Lived Climate Pollution, by R.T. Pierrehumbert the paper is wprth reading. 

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  11. Very interesting graphics, but please SkS, turn off the enhancing glass: it hinders me from taking the link of the graphics .. (anybody who wants to see bigger graphics use the browsers Ctrl/Cmd-"+" key: it's a nice looking gimmick, but for me it's disfunctional).

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  12. Ok, I saw the "documentary" called Cowspiracy a while back, and although it paints the silly black and white picture that "meat is a big problem hence one should ignore all other emissions" I wondered a bit about their numbers. I see they have a number of cited sources on their web page. 18% of all greenhouse gases. I would assume they then also mean the production of food for the meat industry itself as well. How about transportation, does the chart above separate transportation within the agriculture or does it add that to the agriculture number? I do however think the film has a valid point about water usage which adds up a lot for every kg of beef compared to just eating the vegetables ourselves.

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  13. Nice post.

    Can you please just clarify how are trucks, tractors and other machinery included in this analysis? Are they part of the transportation or animal and plant production.

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  14. Those flow charts are a great visual resource. Very informative. It's a great way to communicate that any single solution would only tackle a small part of this huge problem. We need lots of these solutions.

    Any idea if there's an updated version of it? Would the SkS team consider doing it?

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  15. I don't know if this comes from that Cowspiracy movie, but on another website I saw someone make the comment that we're projected to use up all of the 565GT of remaining budgeted carbon emissions through livestock by 2030. It's a completely absurd statement, but there it was. I asked where they got the information but the person didn't respond.

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  16. Re the "documentary" Cowspiracy, it includes every possible factor related to animal agriculture to arrive at their cited percentage of emissions, from land use changes and deforestation, to production of fertilizers for feed crops, to transport of those chemicals and feeds, etc, etc, factors that are already accounted for in other categories. They then compare their resulting aggregate figure to just the direct emissions of transport, which is a rather dishonest slight of hand.

    A proper and honest comparison would be to include a portion of the many factors related to transport, including the overwhelming bulk of petroleum extraction and refining emissions, perhaps the bulk of cement production (roadways, runways, canal locks, etc), a portion of deforestation and land use changes (construction of roadways, airports, docklands), a large portion of steel and aluminum mining and refining and chemical and  machinery manufacturing (cars, trucks, busses, trains, planes, ships).

    Doing so would obviously make for a much more apples to apples comparison, but it would hardly serve the purpose of the film, which is promoting veganism.

    For more see:

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    Moderator Response:

    [RH] Hotlinked URL's.

  17. Thank you so much for this post Dana. I have been waiting for a post on agricultural emissions for some time and was at the point of requesting that you address this gap in the SKS resource library. 

    I am particularly interested in this topic as I own a grass fed beef farm. I have been struggling to find a sensible discussion forum that concentrates on the problem that I am contributing towards (searches on this topic primarily direct to the work of Allan Savory, about which I am rather sceptical). 

    On a personal note, I have begun the process of reducing my stock numbers by 40% on 1990 levels by 2030. I have set up a nursery to grow native trees for revegetation of land that is not grazed (my land is not suitable for arable production). Fertiliser input is almost zero. I am fortunate to have a secondary income that allows me to make these changes - other farmers around me do not have that luxury. 

    I am happy to discuss these choices.

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  18. Can someone specifically discuss the points made in this report by the Worldwatch Institute?

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  19. This "rebuttal" misses several key aspects of the contribution of animal agriculture to anthropogenic greenhouse gas emissions:

    1. As Tom Curtis (#4) points out, methane is a significant player in the short term. Over a short term horizon, say 20 years, methane has a CO2 equivalence factor of 86. Even if each molecule of methane becomes a molecule of CO2 with a half-life of 12.4 years, the fact that atmospheric concentrations of methane have been monotonically rising over the past century shows that the arguments of Pierrehumbert etc., are shooting false straw men. The 1.8ppm of methane that existed in the atmosphere 12 years ago has added 1.8ppm of CO2 to the atmosphere this year, which is a significant fraction of the 2.34ppm of CO2 added to atmosphere from Oct 2014 to Oct 2015. This is significant.

    2. As Andy Skuce (#3) points out with the XKCD graphic, the biomass of livestock grossly exceeds the biomass of humans and wild mammals. Livestock are an invasive species in most ecosystems and as Anthony Barnosky shows, our use of fossil fuels has allowed us to increase the biomass of megafauna from 200Mt to 1500Mt, most of which is livestock. Therefore, the breathing contribution of livestock should be considered an anthropogenic addition to the carbon cycle. Livestock is estimated to cause 8.7Gt of CO2 emissions through breathing alone. This is significant.

    3. Finally, animal agriculture uses 35% of the ice-free land area of the planet for grazing alone. The foregone carbon sequestration from the potential reforestation of this land is calculated to be at least 265 GtC (please note, this is C not CO2) as we show in our upcoming paper to be presented at the AGU Fall Meeting in a couple of weeks. This is significant.

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  20. saileshrao @19:

    "The 1.8ppm of methane that existed in the atmosphere 12 years ago has added 1.8ppm of CO2 to the atmosphere this year, which is a significant fraction of the 2.34ppm of CO2 added to atmosphere from Oct 2014 to Oct 2015."

    That is not correct.  The 12.4 years "lifetime" of CH4 in the atmosphere is the "e-folding time", designated by the unit τ (greek lower case tau).  That means of the 1.8 ppmv of CH4 in the atmosphere 12 years ago, approx 1.1 ppmv will have decayed to CO2 over  the intervening 12 years.  A further 0.4 ppmv will decay over the next 12 years, and another 0.2 ppmv in the twelve years after that.  As CH4 emissions are sufficient to maintain and even increase CH4 concentration against this rate, a better way of looking at it is that CH4 emissions contribute 1.8 ppmv every 12.4 years (assuming equilibrium has been reached), or 0.15 ppmv per annum.  More accurately, at equilibrium the contribution to CO2 from CH4 decay equals the CH4 emission rate.

    Further, you have assumed that 100% of CO2 from CH4 decay is retained in the atmosphere whereas in fact, just like direct CO2 emissions, the airbourne fraction will be about 50%.

    If atmospheric CH4 was allowed to rise to equilibrium concentration with current emission rates, the CO2 concentration per annum (0.017 PgC) would represent 0.425% of current direct CO2 emissions.  That is small enough to be inconsequential except in the very long term (and possibly even then).

    Turning to Pierrehumbert's claim - his point is that in the long term, and assuming CH4 emissions are stabilized, the anthropogenic effect on Earth's temperature is entirely governed by CO2 emissions - which to a first approximation is correct.  CH4 emissions strongly influence how we approach that long term temperature increase.  With initially high CH4 emissions we will approach it rapidly and then possibly settle back down to it.  With low CH4 emissions we will approach it slower.  Therefore, in Pierrehumbert's opinion tackling direct CO2 emissions is the first priority.  He is mounting a counter argument to the claim that industrial emissions of CH4 and black carbon represent "low hanging fruit" that can be tackled cheaply and quickly while largely ignoring the CO2 problem.  Pierrehumbert is correct in rejecting that approach - but I (and no doubt he) believe that we can tackle both at once.

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  21. While I certainly agree with the gist of the article, the Vegan sites have grossly exagerated the effect of animal husbandry, even this article is probably exagerating the impact somewhat due to flaws inherent in a methodology that primarily focuses on emissons rather than complex biological cycles. Emissions focussed methodology works great when we talk about fossil fuels and concrete, because those sources of carbon are from stable pools. The active pools act in a fundamentally different manner. For example, counter intuitively, land use change from forest to pasture can actually can actually have an overall cooling effect rather than a warming effect.

    What matters is the net flux from stable to active carbon cycles. Basically we are talking the stable soil carbon fraction and fossil fuels as the stable pools, and the rest of the carbon that cycles actively is just part of life. There are frozen methane clathrates in the ocean and permafrost that can be a concern should they melt rapidly, but that's more of a feedback concern, if we fail to get the other pools stabilized. More of a symptom that magnifies, not an initial cause. This is one of the things, that if it happens, will dramatically amplify the seriousness of AGW.

    Any agriculture of any type that increases the stable carbon pool in the soil is not creating AGW, but rather is helping mitigate AGW.

    So when you discuss the issue with Vegan advocates intent on humanity giving up animal foods, point out that rather the solution is using agricultural methods that increase soil carbon at a higher rate than they use fossil fuels, for a net reduction in atmospheric greenhouse gasses back into the stable pools.

    If anyone wants to help mitigate AGW by giving up certain foods, give up foods produced from land decreasing in soil carbon, and replace it with food produced from land increasing in soil carbon.


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  22. IMO, lifestock methane should be treated differently to other sources of methane (e.g. fugitive emissions from mining) because their carbon is part of C exchange within OA reservoir. But statements like this:

    ruminant animals like cattle produce methane, which is a greenhouse gas about 20 times more potent than carbon dioxide

    if taken out of context, create confusing scare campaign.

    Apart from short CH4 lifetime, (subject to oxidation to CO2 by hydroxyl radicals within a dacadal timescale) I would like to add that the resulting CO2 does not contribute atmospheric CO2 rise. The carbon that ruminants expell, comes from vegetation that grew by assimilation of CO2 by photosynthesis in the first place.

    It would be a different story if said CH4 came from the "old carbon" (e.g. milion y old fossil fuels). And this is the case of fertiliser input that comes from fussils. This is what really counts in the long term. So, livestock input to global warming (also manure and rice cultivation) is really exaggereted in the figure IMO. Oil/gas extraction and coal mining (fugitive emissions) are of much more dire consequences.

    With the above in mind, in response to foolonthehill@17: if your "fertiliser input is almost zero" (I guess zero fossil fertiliser), then you are fine, nothing to feel sorry with respect to C emissions. Of course, you need to follow other sustainable practices to make sure your land is not dagraded but that is outside of the scope of this forum.

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  23. Thanks very much for this much needed rebuttal Dana, but (yes sorry, always a 'but'!) for the scientifically challenged can you;

    (a) explain why carbon in the short term carbon cycle is not treated differently or (apparently) offset against carbon sinks in the pasture, soils and feed crops within the animal raising agricultural systems? Wouldn't the distinction between fossil fuel sourced emissions be much greater if it was?


    (b) one would expect that the American emissions would be close to worst case (being heavily dependant of industrial feedlot production. When defending oneself against rabid vegans of the 'you can't eat meat if you want to save the world' school - are there examples in the literature about best case, grass fed meat production?

    Maybe it is just wishful thinking, but isn't this at least feasibly a carbon negative pursuit especially when carbon sequestration in healthier soils is taken into account?


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  24. chriskoz @22, a very good point, and one I should have picked up @20.

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  25. lorainel @18 - Stephen Walsh provided a useful critique immediately after the Goodland and Anhang analysis was released. I've filled in some additional details here, though the criticism is essentailly the same as Walsh's.

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  26. Tom Curtis @20:

    Pierrehumbert's assumption clearly does not match reality where methane concentrations in the atmosphere have been monotonically increasing year after year.

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  27. @ lorainel #17

    The issue is that you have two complex factors involved, one is the fact that feedlot beef is fed from cropland, and it does take substantial amounts of fossil fuels to run the tractors, fertilizers and insecticides made from fossil fuels, harvest the grain, dry the grain, ship the grain, turn various mixtures of grain/silage/hay into feed suitable for cows, ship the feed again. Not to mention you have to load up the beef cows and transport them live to the feedlots in the first place. There is a big difference between that and a cow simply walking over to the next fresh pasture. Feedlot production is very inefficient in terms of fossil fuel use.

    Then there are unexpected emergent properties of the system as well, compared to pasture, cropland also has a much lower community of methanotrophs, and mycorrhizal fungi, both of which are responsible for sequestering large quantities of greenhouse gasses. You could look at them as carbon pumps into the soil via the grassland's symbiotic relationships. So as it turns out, cows raised on properly managed pasture end up being part of a larger net carbon sink, not a net carbon emissions source, while cows raised in feedlots are an even larger emissions source than commonly known when you include the cropland supplying the feedlot.

    Nevertheless, even as bad as feedlots can be, they are not as bad as the exaggerated claims by certain Vegan propaganda sites, which have exaggerated their impact on AGW, to take advantage of the new "sexy" environmental awareness campaigns on global warming mitigation. They basically do this by first cherry picking the harmful parts, ignoring anything that doesn't promote their dogma like the 1/2 life of methane in the atmosphere, and then double counting things like transportation, cropland emissions etc. Finally the fallaciously claim that eliminating meat consumption is the solution, rather than changing the management and production methods.

    You also proclaimed your skepticism of Savory, the leading scientist in the field of rangeland management. OK skepticism is fine, I am a skeptic myself. However, to be a really good skeptic requires study. This may help. 


    I think the more you study it, the more plausible Savory's work becomes, athough in the beginning, most people find it counterintuitive. Real hard to argue with the results though. For your personal ranch, I wouldn't worry too much about the impact to AGW. You have a grassfed production model, so more likely than not you are mitigating AGW  rather than causing it, assuming you are properly managing it for that purpose. Keep in mind undergrazing can be just as bad as overgrazing in certain climatic conditions. But as long as your management plan includes proactive monitoring, you'll be able to figure that out soon enough.

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    Moderator Response:

    [RH] Shortened link that was breaking page format.

  28. saileshrao @26, in the 322 months from April 1987 to Jan 2014, using Mauna Loa data, 142 had 12 month average CH4 concentrations less than the maximum 12 month average concentration to that date (most recent: April 2013.  10 of the 27 annual averages over that period are less than the maximum to date (most recent: 2006).  In short, CH4 concentrations are not increasing monotonically.

    The Pierrehmbert quote again was:

    "A re-examination of the issues shows that the benefits of early SLCP mitigation have been greatly exaggerated, largely because of inadequacies in the methodologies used to compare the climate effects of short-lived substances with those of CO2, which causes nearly irreversible climate change persisting millennia after emissions cease. Eventual mitigation of SLCP can make a useful contribution to climate protection, but there is little to be gained by implementing SLCP mitigation before (my emphasis) stringent carbon dioxide controls are in place and have caused annual emissions to approach zero."

    Again, he is not saying that addressing Short Lived Climate Pollution is pointless, but only that it is a second order priority to reducing CO2 emissions.  The reason for that is that the effects of SLCP in general, and of CH4 in particular will be negligible after 100-200 years, whereas the effects of CO2 emissions will persist for thousands and even tens of thousands of years into the future.  Three hundred years from now, current CH4 emission rates will be a matter of historical interest only; whereas current CO2 emission reates will be having ongoing negative impacts.  Prioritizing effects which are beneficial only over the short term ahead of effects that will persist longer than our civilization shows somewhat distorted values.

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  29. Reason_4 @ 23 - you have to consider what the land would be used for if it weren't being used for livestock pasture land.  For example, when forest land is replaced by pasture land, that's actually a decrease in natural carbon sequestration.

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  30. RedBaron @27 - Re: Savory - plausability is nice but reproducability is better.

    'Holistic management does not permit replication. Because of this fact we can only validate the ‘science’ used and monitor or document ‘results achieved’. Note: This point is critical to understanding the great difficulty reductionist scientists are experiencing trying to comprehend holistic planned grazing – because no two plans are ever the same even on the same property two years running, planned grazing cannot be replicated which reductionist scientists do to try to understand the ‘science.’

    from here


    If one replaces 'holistic management' with 'homeopathy' then maybe you can understand my scepticism.

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  31. Dana @29

    I appreciate that, although as a permaculturalist I also understand the reverse is also possible (you can take already degraded land and dramatically improve carbon sequestration in a system that may well integrate raising animals to further enhance this aspect).

    But I'm still curious about the first point - why some animal emissions are tallied (eg methane from ruminant animals) and others not (CO2 respiration from any animal) and then listed as equivalent to the same emissions from fossil fuels (either burnt or fugitive) when one is effectively carbon neutral in the short term carbon cycle ... and the other definitely isn't. 

    We (of course) dismiss deniers who suggest humans need to stop breathing/belching/farting ... why are some livestock emissions treated differently?

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  32. TomR was spot on about the weight mistake the EWG chart makes.  Consider the FAO report "Tackling Climate Change through Livestock" (2013), page 16, figure 3 where you will find a chart graphing against protein content.  What may surprise some vegetarians is that Milk is hardly one of the lowest as indicated in the EWG graph, but actually is higher in CO2e per kg of protein than some meats like pork or chicken.  This is due to the previously discussed massive amount of methane produced by ruminants- a byproduct of cellulose breakdown by methanogen microbes in their guts.  

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  33. Saileshrao #26:
    "....where methane concentrations in the atmosphere have been monotonically increasing year after year."

    Not between 1999 and 2007, and much less after 2007 than before 1992!


    Also note that the forcing growth rates from GHG’s other than CO2 decreased rapidly in the 1990’s.

    Forcing growth rates

    So, when it comes to methane, I’m more worried about emissions from thawing permafrost and other possible feedbacks than directly from human activity that we can control.

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  34. Reason_4. Carbon is cycling all the time. Plants absorbs it CO2, plant decays and returns CO2 to atmosphere. Animals/humans eating plant and emitting CO2 is slight variation from this schedule. Breathing by any animal is carbon neutral -none of this changes net CO2 in atmosphere (unlike releasing fossil carbon). Ruminants are slightly different. A portion of plant carbon is released as CH4 instead of CO2 and it takes time for the CH4 to be oxidized to CO2. Over the time period before oxidization, there is more GHG effect than you would have if you had no animals (or no ruminants). The calculation of greenhouse gas potential for agricultural emissions is not a trivial calculation.

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  35. Reason_4, CO2 from respiration is not counted because it is 100% carbon neutral: the C respired into CO2 came from the plant matter eaten by the livestock, which came from CO2 in the atmosphere. There is no new CO2 and thus no additional forcing.

    The methane emitted by ruminants also came from the same source (atmosphere CO2 > C in plants), but it is counted because it is emitted as CH4 rather than as CO2, which produces a greater forcing than the original CO2 until it is oxidized into CO2.

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  36. @scaddenp #34

    Please supply some citation showing that this statement "there is more GHG effect than you would have if you had no animals (or no ruminants)." has been properly analysed and is true. Methanogens are microorganisms that produce methane as a metabolic byproduct in anoxic conditions. That certainly is true. But they are certainly not unique to ruminants. In fact methogen archaea are ubiquitous in the environment and soils. In some areas for example termites far exceed the methane production of any ruminants. Nor are methogen archaea the only source of methane produced by decomposition and incomplete oxidation of the products of photosynthesis. Nor is methane oxidation in the atmosphere the only way to reduce methane to CO2 as methanotroph prokaryotes are also ubiquitous in many environments. I have yet to see any documentation of any analysis of methane production that proves ruminants increase atmospheric methane over other forms of decomposition or incomplete oxidation of organic material except in the artificial feedlot/cess pool production model. And even then the methane can be collected and used as a biofuel.

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  37. RedBaron, i am in no way claiming that ruminants are only source of biological methane. I am really claiming that if you increase the number of ruminants (in particular since pre-industrial benchmark), then you are getting more methane into the atmosphere than if you had left them at preindustrial level. Increase in methane from any source is a concern, but the to-date, increase in ruminants is a major source. Numerous papers on this cited in IPCC report and working groups on methane. A review paper here could be starting point. Other sources of anthropogenic methane including paddy agriculture, landfills, manmade lakes/wetlands and waste treatment are considered in CH4 inventories. Table 5.8 in  IPCC AR5 WG1 report lists source of methane with references. (Ruminants contributing 89 Tg/year of the total anthropogenic source of 331). The same table also lists natural sources but for consideration of change in methane level (and hence warming), it the change from pre-industrial at matters.

    Note also that 2/3 of methane production from cattle is enteric rather than from manure.

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  38. Thanks to scaddenp for the reference to table 6.8 (not 5.8, sorry), on page 507 of the AR5 WG1 report.  It shows that in the interval 2000-2009, rice cultivation contributed 36 Tg/year to the total 331 Tg/year of anthropogenic methane emissions, compared with 89 Tg/year for ruminants. I'm not surprised that vegans aren't calling for an end to rice production, however.

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  39. What matter with paddy production though is how much is it changing? Absolute emissions arent as interesting as how much change has occurred in 20-21 century.

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  40. @scaddenp #39

    That is an excellent point. Sometimes people, even great scientists, get so wrapped up in the minutia of detail, they overlook the the bigger picture. The same thing that can be asked about rice paddys can be asked about meat production. How is it that the grassland/grazer biome responcible for long term global cooling on the planet, is now contributing to warming? (see post #21) What has changed since the industrial era? If you approach the problem from that perspective, I think the science is where the change in production methods might change the fundamental balance in the carbon cycle. That's where your interesting research can be found. What are the differences between a grassland/grazer biome and a cropland biome where the animals have been removed and instead raised in CAFOs? Rather than blame the animals themselves for AGW, I personally think the only conclusion anyone can make is the production methods have changed.

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  41. Tom Curtis @28, HK @ 33,

    Pierrehumbert's argument is that methane concentrations in the atmosphere will decay exponentially with a short half-life of 12.4 years. That is clearly not the case in reality as we continue to pump fresh methane into the atmosphere year after year, while pretending that methane is benign compared to CO2.

    1 0
  42. Jim Eager @ 35,

    Livestock is NOT in equilibrium with the environment as the accelerating desertification of grasslands and pasture lands clearly shows. Indeed, the biomass of livestock megafauna today is 5.5 times the biomass of ALL megafauna from prehistoric times! Therefore, the breathing contribution of livestock is an anthropogenic contribution to the imbalance in the Earth's carbon cycle.

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  43. @scaddenp and Jim Eager @ 34 and 35

    I'm well aware of the difference in warming/forcing potential between CO2 and CH4.

    I am still mystified why fugitive CH4 from fossil fuel extraction or transport seems to be treated in the same way that CH$ from ruminant livestock is treated or accounted for.

    Yes, both have the same forcing potential, but one is at least carbon (not forcing) neutral while the other ... isn't.

    Let me try another way. We have yet to raise ruminant animals on our mini farm, but more from lack of knowledge and unwillingness to be tied to the property 365 days a year than for any environmental concern. But it is in the long term plan.

    When we do I want to be well armed to defend our choice against those that say we are destroying the planet by keeping cattle or sheep. I will hopefully convince someone from the local Uni to take some before and after soil samples to demonstrate the increased carbon sequestration nutrients from large animal manure helps create. If we can point to greater carbon sequestration than is likley to be emitted, and there is no need for externally sourced feed or fertilisers, we would be justified in stating the meat we produce is carbon negative ... right? 

    If we can justifiably make that claim ... again, just why is fossil fuel sourced methane treated exactly the same as livestock sourced - because if that is all that is counted, our carbon negative cattle ... are anything but. Right?

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  44. I think we have established that the long term impact of livestock methane emissions is likely to be very low (when we consider that it will decay to CO2), zero (when we consider that the emitted carbon is essentially re-cycled from the atmosphere to begin with), or even negative (when we consider carbon sequestration from waste).

    Given this plausible range of 'very little harm' through 'some benefit' it seems clear that we can pretty much ignore the issue. Long term, methane from livestock isn't going to be a problem. The same can probably be said, for similar reasons, of methane from rice production and even landfills. Methane from fossil fuels doesn't have the 'recycling' and 'sequestration' conditions, but it still decays to CO2 and thus will have a small long term impact... especially as it will inherently decline if/when we get the much larger direct CO2 emissions from fossil fuels under control.

    Ergo, I would argue that we can all but ignore methane for long term planning purposes. We need only look at its 'short term' (e.g. through 2100) impact. Unfortunately, given Tom's analysis and IPCC flow diagram, there I do see a problem. So long as the human population continues to grow I see very little chance of preventing methane emissions from livestock, rice, and landfills from also growing in response. That will mean continually increasing emissions and atmospheric levels. In one sense, these human activities which temporarily convert some of the CO2 to methane are one of the 'sinks' slowing the growth of atmospheric CO2 levels... which unfortunately results in a net warming increase. That means, short of radical changes to the global food supply and/or waste handling, the 'short term' warming from methane will continue to grow so long as the global population does.

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  45. CBDunkerson @44, an excellent summary.  It is, however, a little over pessimistic.  Research is being undertaken into how to reduce methane from enteric fermentation  and from rice cultivation.  Further, given that amospheric methane concentrations must be near the equilibrium value for current emissions (else the plateau of  concentration over the 1990s would not have occured) such measure may feasibly limit future growth in CH4 concentration - although it is dubious,  in the face of the need to feed a more than doubling of the human population, that they  will permit a decease in concentration.  Of greater concern in that regard is NO2, whose longer residence time means it is nowhere near equilibrium, and where reduction of agricultural emissions is more limited in potential scope.

    The point remains, however, that the key task in to reduce CO2 emissions.  That is not only because it is CO2 emissions alone that will cook us long term, but also because tackling CO2 emissions is likely to lead to the technology to generate slightly negative net emissions of CO2 as a compensation of whatever persistent forcing from CH4 and NO2 exists. 

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  46. Saileshrao, sorry, but simply asserting that livestock respiration is anthropogenic does not make it so. It is still atmospheric CO2 in, atmospheric CO2 out. Overgrazing degradation of range land and desertification are serious but separate issues.

    saileshrao: "biomass of livestock megafauna today is 5.5 times the biomass of ALL megafauna from prehistoric times!"

    Citation please. The pre-European population of North American bison alone was in the order of 20-30 million.

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  47. Reason_4: "I am still mystified why fugitive CH4 from fossil fuel extraction or transport seems to be treated in the same way that CH4 from ruminant livestock is treated or accounted for."

    Simply because the atmosphere does not care where the CH4 comes from, the additional forcing is the same regardless.

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  48. @Jim Eager @47 

    Not sure how I can explain this better, but lets make it even simpler.

    If I release 1 ton of methane (yes regardless of source) that results in a certain amount of forcing ... right?

    If I release 1 ton of methane AND at the same time sequester 5 tons of CO2 there is still some NET forcing ... but not as much as in the first example ... right?

    This net result is why we (of course) don't count CO2 emissions from respiration (not just because CO2 is a less potent GHG than methane, but because the net result is zero)

    This is my very simple question regarding emissions from livestock. Why do we not look at the emissions AND the source of the carbon in those emissions AND any associated sequestation that arises as a result of raising livestock - and then arrive at a net figure for the whole operation.

    Fossil fuel sourced methane is simple - we know the source, so no short term carbon cycle to allow for there ... right? and until there is finally some actual commercial CCS projects run in association with extraction, there is no sequestration adjustment necessary to arrive at a net forcing either ... right?

    If we don't examine the net forcing arising from 'animal agriculture', how can we say that we are addressing the question raised by Dana in the title of this article ... accurately?

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  49.  Redbaron - please see this paper. Soil carbon loss under intensive dairying is a substantial issue here in NZ and the subject of research eg (here). It looks like intensification of agriculture is not good for carbon soil stocks.

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  50. Jim Eager @46:
    Please see, e.g., Anthony Barnosky's paper in PNAS,

    and Vaclav Smil's book, "Harvesting the Biosphere: What We Have Taken From Nature":

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