When “revelations” about methane emissions are not revelations at all

Dr Frank Mitloehner is a professor at the University of California, Davis (UCD). He is qualified in agricultural engineering and animal science.

According to his UCD bio, his research has focused on air quality (dust emission and microbial sampling in pigs and feedlot cattle), environmental physiology (heat stress in pigs and cattle), animal behaviour, air quality related to farmed animal production (including ammonia, dust, and odour emissions in dairies, beef feedlots and poultry operations), “environmentally benign” farmed animal systems, and environmental physiology focusing on the effects of air emissions on animal health. [1]

Although he would not appear to be a climate scientist, he has commented extensively on climate issues in favour of the animal agriculture sector. He has also disclosed research funding from the National Cattlemen’s Beef Association. [2]

Two examples of his comments have involved Alltech, an American company focusing on animal health and nutrition, crop science, coffee and alcoholic beverages. The first example was an interview with the Alltech’s head of sustainability, David Butler, in June 2019. The second was his presentation at ONE20: The Alltech Ideas Conference, in May 2020. [3] [4]

In both, he focused on methane (CH4), a potent greenhouse gas that is prominent in animal agriculture. Two key points seemed to be conveyed as revelations when they were not revelations at all. Various other points in his communications were questionable.

He feels that mainstream media has ignored the issues raised but the lack of interest may simply reflect the fact that the fundamental points are not new or lack merit.

Methane’s relatively short lifetime

One of Mitloehner’s key points was that methane is removed from the atmosphere much faster than two other prominent greenhouse gases, carbon dioxide (CO2) and nitrous oxide (N2O).

That point is well known and allowed for in estimates of methane’s global warming potential (GWP) from the UN’s Intergovernmental Panel on Climate Change (IPCC) and elsewhere. As such, Mitloehner’s argument that methane’s impact is overstated seems invalid.

A GWP rating is a multiplier which reflects the climate forcing of a greenhouse gas over a specified time period relative to that of carbon dioxide.

Indeed, the extent of methane’s impact over a time horizon of ten or twenty years is generally under-appreciated due to the fact that reporting bodies usually cite figures based on a 100-year time horizon.

A 20-year time horizon increases the GWP multiple from 34 (allowing for climate-carbon feedbacks) to 86. That is to say that methane’s climate forcing impact is 86 times that of carbon dioxide over a 20-year period. Without the climate-carbon feedbacks, the multiples are 28 for 100 years and 84 for 20 years.

The IPCC has said that both time horizons are valid, with the choice between those or others being a value judgement because it depends on the relative weight assigned to effects at different times. [5]

The difference in results is a critical factor given our proximity to tipping points in the climate system which can cause an abrupt change from one climate state to another. A related factor is feedback mechanisms in the climate system, which can propel us toward runaway climate change over which we will have no meaningful control.

A key benefit of fully acknowledging methane’s impact is that rapid results in addressing climate change can be achieved by reducing emissions of the gas.

Who said methane was a “flow” gas?

Related to the previous point, in supporting a variation of the conventional GWP concept known as GWP* or (GWP star), Mitloehner argues that methane is a “flow” gas and that carbon dioxide and nitrous oxide are “stock” gases. The distinction is subjective.

The argument is that carbon dioxide and nitrous oxide are long-lived greenhouse gases that accumulate in the atmosphere while methane is a short-lived gas that does not. However, the USA’s National Oceanic and Atmospheric Administration (NOAA) regards methane as long-lived. The IPCC regards it as a “well-mixed” gas, while noting that others sometimes describe such gases as “long-lived”.

The position of NOAA and IPCC is supported by the fact that methane does indeed accumulate, with atmospheric concentrations having increased markedly since the pre-industrial period and in recent decades, as demonstrated by Figures 1, 2(a) and 2(b). [6] [7] [8]

The atmospheric concentration of methane has increased around 170 per cent (or a factor of 2.7) since pre-industrial times compared to around 50 per cent (a factor of 1.5) for carbon dioxide.

Figure 1: Global average abundances of the major, well-mixed, long-lived greenhouse gases CO2, CH4, N2O, CFC-12 and CFC-11 from 1975 to 2020

Figure 2(a): Global Methane Levels from year 1000 to 2020

Figure 2(b): Global Carbon Dioxide Levels from year 1000 to 2020

Writing in the journal Science in 2019 regarding rising atmospheric methane concentrations, Sara Mikaloff Fletcher and Hinrich Schaefer reported that changes in the ratio of carbon-12 and carbon-13 isotopes within methane molecules indicate that biogenic sources may be a major contributing factor in combination with other processes. Of the biogenic sources, ruminant livestock emissions are believed to account for about half the increase since 2007. [9]

In July 2020, articles in Earth System Science Data and Environmental Research Letters and related media coverage highlighted the rapid recent increase in methane concentrations. They reported that emissions from cattle and other ruminant animals were the main cause of the increase and were almost as large as those from the fossil fuel sector in the periods under review. [10] [11] [12]

Mitloehner claimed in the Alltech interview that carbon dioxide and nitrous oxide stay in the atmosphere “for hundreds, if not thousands, of years”.

That claim is overstated and not supported by the IPCC, which has noted [Footnote 1]:

  1. Around half of carbon dioxide is sequestered by oceans and terrestrial sinks within decades, with only a small fraction remaining in the atmosphere for thousands of years. [13]
  2. Nitrous oxide’s estimated lifetime is 121 years. [14]

Mitloehner noted a figure of 120 years for nitrous oxide in the Alltech conference presentation but still described it as “hundreds of years”, which it clearly is not.

He has used the “flow” concept to argue that farmed ruminant animal herds of constant size add no additional methane and therefore no warming.

There are some additional problems with that argument.

Firstly, the world has already warmed to a dangerous extent, with devastating outcomes. Whether derived from biogenic or fossil sources, atmospheric concentrations of methane are dangerously high and must be reduced, along with concentrations of other greenhouse gases.

The flow argument is analogous to saying that (for example) a high recurring annual number of road deaths is acceptable, without implementing readily available measures to reduce them.

The second additional problem is that the global cattle population is increasing.

Although the number of cattle in Mitloehner’s home base of USA has fallen 3 per cent since 1961, the number globally has increased 58 per cent, as depicted in Figure 3. [15]

Figure 3: Cattle populations 1961-2018

From 1990 to 2019 beef consumption in the USA increased 13 per cent, while the figure globally was 83 per cent. [16]

Furthermore, the UN Food and Agriculture Organization is projecting global meat production to double by 2050. [17]

The GWP* concept referred to earlier was developed by Myles Allen and Michelle Cain from the University of Oxford and fellow researchers. [18] [19] Seemingly contrary to comments from Mitloehner, it does not appear to have been widely accepted, and the initial version was met with some skepticism at the 24th Conference of the Parties (COP24) to the United Nations Framework Convention on Climate Change (UNFCCC) in Katowice, Poland. [20]

The latest version has been said by IPCC lead author Professor Pete Smith of the University of Aberdeen and Professor Andrew Balmford of the University of Cambridge to represent a form of “creative accounting”. [21]

GWP* is one of many alternatives to the conventional GWP metric.

The fact that the government of New Zealand (population 5 million) has taken it into account in maintaining a certain level of methane emissions from farmed animals within its inappropriately named “Zero Carbon Act” may reflect the farmed animal sector’s large share of the nation’s emissions, and the fact that GWP* is more rewarding of reductions in methane emissions than is conventional GWP.

A recycling process involving carbon on steroids

Mitloehner has noted that atmospheric methane is broken down over time by the hydroxyl radical (OH). The carbon within the methane molecule is converted in that process to carbon dioxide, some of which can then be absorbed by vegetation and other carbon sinks.

That point seems barely worth mentioning, as the breakdown (as noted earlier) is already allowed for in estimates of methane’s climate forcing impacts.

Mitloehner himself has noted the high potency of methane relative to carbon dioxide.

It has been described by Kirk Smith, Professor of Global Environmental Health at the University of California, Berkeley, as “carbon on steroids”. [22]

Figure 4: Methane: “Carbon on steroids”

The fact that the carbon may eventually be absorbed by vegetation and other sinks provides little comfort when one considers its adverse impacts while it exists in the form of methane.

Grass-fed versus grain-fed cattle

In his Alltech interview, Mitloehner pointed out that animals “finished” on grass produce more methane than those “finished” on grain. That was another “revelation”.

However, the point is also well-known even though many commentators and environmental groups erroneously assume and state the opposite.

Researchers from the USDA’s Agricultural Research Service, Texas A&M University and Australia’s CSIRO reported in 1999 that ruminant animals eating grass produce methane at four times the rate of those eating grain. [23] [Footnote 2]

Similarly, in 2010, Professor Gidon Eshel of Bard College, New York and formerly of the Department of the Geophysical Sciences, University of Chicago, reported, “since grazing animals eat mostly cellulose-rich roughage while their feedlot counterparts eat mostly simple sugars whose digestion requires no rumination, the grazing animals emit two to four times as much methane”. [24]

Based on David Butler’s response of “wow, that’s interesting” to Mitloehner’s comment, it seems he was impressed.

Efforts to reduce methane emissions through the use of feed supplements face key logistical difficulties and may largely be limited to dairy and feedlot animals, where their inclusion is a straightforward process. The emissions intensity of products derived from those animals is already lower than that of animals fed only grass and used specifically for beef production, meaning the benefits of supplements may be lower than they may otherwise have been.


Whichever way we look at it, methane is a potent greenhouse gas that has been rapidly accumulating in the atmosphere.

Due to its relatively short lifetime, reductions in its emissions offer the opportunity for rapid climate change benefits.

A key source of methane, ruminant animals, represent a grossly and inherently inefficient source of nutrition. With the social and political will to do so, we could readily replace them with highly efficient, low carbon, non-animal sources.

Such a measure is essential if we wish to retain a habitable planet.


Paul Mahony


  1. The lifetimes mentioned by the IPCC are the perturbation lifetimes, which allow for the effects of the relevant greenhouse gases arising from chemical feedbacks. Around two-thirds of methane is broken down in around 12 years and the same proportion of nitrous oxide within around 120 years. [25] [26]
  2. Although the CSIRO subsequently reported a reduction in emissions from the northern Australian cattle herd, emissions from grass-fed cattle remain on a different paradigm to those of most food-based emissions.


[1] University of California, Davis, Department of Animal Science https://animalscience.ucdavis.edu/people/faculty/frank-mitloehner

[2] Goodland, R., “FAO’s New Parternship with the Livestock Industry”, Chomping Climate Change, 20th July, 2012, http://www.chompingclimatechange.org/blog/faos-new-parternship-with-the-livestock-industry

[3] McCormack, C., “Latest science on methane emissions ‘ignored’ by media – Dr. Mitloehner”, AgriLand, 26 May 2020, https://www.agriland.ie/farming-news/latest-science-on-methane-emissions-ignored-by-media-dr-mitloehner/

[4] Alltech, “Frank Mitloehner: Cattle, climate change and the methane myth”, 25 June 2019 https://www.alltech.com/features-podcast-blog/frank-mitloehner-cattle-climate-change-and-methane-myth

[5] Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: “Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group 1 to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change”, pp. 711-712, [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, http://www.ipcc.ch/report/ar5/wg1/

[6] Butler, J. and Montzka, S., The NOAA Annual Greenhouse Gas Index (AGGI) updated spring 2020, https://www.esrl.noaa.gov/gmd/aggi/aggi.html

[7] Myhre, G., et al., op. cit., Box 8.2, p. 668

[8] 2 Degrees Institute, https://www.2degreesinstitute.org/, https://www.methanelevels.org/ and https://www.co2levels.org/

[9] Mikaloff Fletcher, S.E., and Schaefer, H., “Rising methane: A new climate challenge”, Science  07 Jun 2019: Vol. 364, Issue 6444, pp. 932-933, DOI: 10.1126/science.aax1828, citing Wolf, J., Asrar, G.R., West, T.O., Carbon Balance Manag. 12, 16 (2017) in respect of ruminant livestock emissions. https://science.sciencemag.org/content/364/6444/932

[10] Jackson, R.B., et al 2020 Environ. Res. Lett. 15 071002, https://doi.org/10.1088/1748-9326/ab9ed2

[11] Saunois, M., et al 2016 Environ. Res. Lett. 11 120207, https://doi.org/10.1088/1748-9326/11/12/120207

[12] Guy, J., “The world’s methane emissions are at a record high, and burping cows are driving the rise”, CNN, 15 July 2020, https://edition.cnn.com/2020/07/15/world/methane-emissions-record-scli-intl-scn/index.html

[13] Ciais, P., Sabine, C., Bala, G., Bopp, L., Brovkin, V., Canadell, J., Chhabra, A., DeFries, R., Galloway, J., Heimann, M. and Jones, C., 2013. Chapter 6: Carbon and other biogeochemical cycles. Climate change 2013: the physical science basis. In: Tignor et al., (Eds.) Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge and New York: Cambridge University Press, pp. 472-473, cited in Parliamentary Commissioner for the Environment, “Farms, forests and fossil fuels: The next great landscape transformation?”, March 2019, p. 98. https://www.pce.parliament.nz/publications/farms-forests-and-fossil-fuels-the-next-great-landscape-transformation and https://www.pce.parliament.nz/media/196523/report-farms-forests-and-fossil-fuels.pdf

[14] Myhre, G., et al., op. cit., Table 8.7, p. 714

[15] Food and Agriculture Organization of the United Nations, FAOSTAT, Live Animals, 1961-2018

[16] OECD (2020), Meat consumption (indicator). doi: 10.1787/fa290fd0-en (Accessed on 26 July 2020)

[17] Food and Agriculture Organization of the United Nations, Agriculture and Consumer Protection Department, Meat and Meat Products, Updated on 20 March 2019, http://www.fao.org/ag/againfo/themes/en/meat/home.html

[18] Allen, M.R., Shine, K.P., Fuglestvedt, J.S., Millar, R.J., Cain, M., Frame, D.J., Macey, A.H., A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation. npj Clim Atmos Sci 1, 16 (2018). https://doi.org/10.1038/s41612-018-0026-8

[19] Cain, M., Lynch, J., Allen, M.R., K.P., Fuglestvedt, Frame, D.J., Macey, A.H., Improved calculation of warming-equivalent emissions for short-lived climate pollutants. npj Clim Atmos Sci 2, 29 (2019). https://doi.org/10.1038/s41612-019-0086-4

[20] Zionts, J., Animal agriculture takes centre stage at COP24, Environmental Change Institute, University of Oxford, 8 Jan 2019, https://www.eci.ox.ac.uk/news/2019/0108-cop24.html

[21] Smith, P., Balmford, A. (2020) Climate change: ‘no get out of jail free card’

[22] Smith, K.R., “Carbon dioxide is not the only greenhouse gas”, ABC Environment, 25th January, 2010, http://www.abc.net.au/environment/articles/2010/01/25/2778345.htm; Smith, K.R., “Carbon on Steroids:The Untold Story of Methane, Climate, and Health”, Slide 67, 2007, http://www.arb.ca.gov/research/seminars/smith/smith.pdf

[23] Harper, L.A., Denmead, O.T., Freney, J.R., and Byers, F.M., Journal of Animal Science, June, 1999, “Direct measurements of methane emissions from grazing and feedlot cattle”, J ANIM SCI, 1999, 77:1392-1401, http://www.ncbi.nlm.nih.gov/pubmed/10375217; https://academic.oup.com/jas/article/77/6/1392/4625488; http://www.journalofanimalscience.org/content/77/6/1392.full.pdf

[24] Eshel, G., “Grass-fed beef packs a punch to environment”, Reuters Environment Forum, 8 Apr 2010, http://blogs.reuters.com/environment/2010/04/08/grass-fed-beef-packs-a-punch-to-environment/

[25] Parliamentary Commissioner for the Environment, op. cit., p. 59 and Table 4.1, page 98.

[26] Myhre, G., et al., op. cit., Table 8.7, p. 714


Featured image: GLF Media, Shutterstock ID 1055789636

Image in cattle population chart: Bear Witness Australia via Aussie Farms

Capsule: Lightspring, Shutterstock ID 1539353021

Methane molecule: LoopAll, Shutterstock ID 560965879


Sentence on supplements within the specialised beef herd added seven hours after initial publication.

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