There are many myths about meat consumption. I focus on two in this article, along with some related issues.
MYTH 1: BEEF PRODUCED FROM GRASS-FED COWS IS BETTER FOR THE ENVIRONMENT THAN GRAIN-FED
It seems logical, doesn’t it? After all, eating grass is natural for a cow. But does that make it better for the environment?
Why wouldn’t you believe the myth when a supposedly authoritative source like the Australian Conservation Foundation says: “When you do buy meat, choose pasture or grass-fed sources over grain-fed ones.” 
To my knowledge, the ACF has not cited any sources to support that statement.
Similarly, no sources were cited by prominent climate change activist Bill McKibben of 350.org when he supported the idea of grass-fed cattle over the feedlot variety in his Orion Magazine article of 2010, “The Only Way to Have a Cow“.  He was maintaining that position during a speaking tour of Australia in June, 2013. [Footnote 1]
Emissions from grass-fed cows are multiples of the grain-fed alternative
On the other hand, Professor Gidon Eshel of Bard College, Annandale-on-Hudson, New York and formerly of the Department of the Geophysical Sciences, University of Chicago, has 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”. 
In Australia, the CSIRO (Commonwealth Scientific and Industrial Research Organisation) has also reported that cows produce significantly more methane when eating grass than when eating grain. It stated, “These measurements clearly document higher CH4 [methane] production (about four times) for cattle receiving low-quality, high-fiber diets than for cattle fed high-grain diets.” 
CSIRO scientists subsequently reported some reduction in methane emissions from northern Australian cattle herds, representing around half the country’s cattle population.  However, that would still leave grass-fed cows’ methane emissions as a multiple of grain-fed emissions.
What does the FAO say?
In November, 2013, the FAO (Food and Agriculture Organization of the United Nations) reported a signficant difference in the greenhouse gas emissions intensity between beef derived from animals on “grazing” (or “grass-based”) feeding systems and those on “mixed” systems.  
The emissions intensity of a product represents the kilograms of CO2-equivalent (CO2-e) greenhouse gas emissions per kilogram of product.
It seems reasonable to conclude that the FAO’s “mixed” figures included grain-fed cattle, as it confirmed “grass-based and mixed livestock production systems” are responsible for 100 percent of global beef production. (Reference 7, p. 24).
Cows are not fed grain exclusively. They have not evolved to consume it, and if it is used at all, they are generally only “finished” on it for the final one hundred days or so prior to slaughter.
For specialised beef (as opposed to beef from dairy cows), the FAO reported emissions intensity figures of 56.2 for mixed feeding systems and 102.2 from grazing systems.
Those figures were based on carcass weight. If we gross them up to allow for the fact that not all the carcass is used as end product for the dinner table, the figures increase to 77.2 and 140.2 respectively. That’s based on the US Department of Agriculture’s mid-range yield estimate of 72.8% for all beef, including ground beef for use in hamburgers and the like. 
We can also gross them up to allow for a 20-year GWP (global warming potential) for methane. Allowing for that factor (refer to additional comments below), the figures increase to 160.1 and 290.9 respectively.
Conventional measures of methane’s global warming impact measure it over a 100-year timeframe. However, methane breaks down relatively quickly in the atmosphere, with much of it doing so within around 12 years. That means the 100-year measure greatly understates its shorter-term impact, as it provides an average figure over a 100-year period, when much of the methane effectively did not exist during the final 88 years. In the chart below, I have used a 20-year GWP of 86 for methane, from the IPCC’s Fifth Assessment Report. It is up from the IPCC’s previous figure of 72, and allows for carbon-climate feedbacks. (Without those feedbacks, the IPCC now uses a figure of 84.) 
Researchers at NASA have estimated an even higher 20-year GWP for methane of 105. 
Although methane may have a shorter life than carbon dioxide (which remains in the atmosphere for many hundreds of years), its impact can be long-term if it contributes to us reaching tipping points that result in positive feedback loops with potentially irreversible and catastrophic consequences. On the positive side, the relatively short-term nature of methane’s impact means that action on livestock production can be one of the most effective steps available to us in dealing with climate change.
Respected climate change commentator, Joseph Romm, has quoted the IPCC [his underlines]:
“There is no scientific argument for selecting 100 years compared with other choices (Fuglestvedt et al., 2003; Shine, 2009). The choice of time horizon is a value judgement since it depends on the relative weight assigned to effects at different times.” 
Romm went on to say:
“Given that we are approaching real, irreversible tipping points in the climate system, climate studies should, at the very least, include analyses that use this 20-year time horizon.”
I have previously compared beef production to aluminium in order to add some perspective to its emission levels. Aluminium production is an incredibly emissions-intensive process. In recent times, it has consumed up to 16 percent of Australia’s electricity production , for less than: 1 percent of GDP (gross domestic product); and 0.1 percent of jobs.
In a 2003 report commissioned by the former Australian Greenhouse Office, its emissions intensity was reported as 20 kg CO2-e per kg of product.  The Australian Aluminium Council has reported a 2011 figure of 15.6 kg (rounded to 16 kg in the table below) for “primary aluminium production, not including emissions from alumina refining which are considered separately”.  It has stated that over 80 percent of smelting’s greenhouse gas emissions are indirect (electricity-related) emissions. The emissions intensity of Australian aluminium is more than twice the global average, due to the heavy reliance on coal-fired power. 
Here’s how beef production compares to aluminium and steel, based on: (i) carcass weight and standard 100-year GWP; (ii) retail weight and 100-year GWP; and (iii) retail weight and 20-year GWP. Beef’s figures vary by region. Those shown here are based on the global average.
Figure 1: Greenhouse Gas Emissions Intensity
So, allowing for a 20-year GWP to more accurately reflect methane’s shorter-term impact, a kilogram of steak is 18 times as emissions intensive as a kilogram of Australian aluminium, and more than 30 times as emissions intensive as aluminium’s global average.
How do other foods compare?
The emissions intensity of the following foods have been reported to be less than 2 kg CO2-e per kg of product even (in respect of some) when transported overseas by boat: whole wheat; rice; carrots; potatoes; green beans; apples; oranges; and soy beans.  That is less than 0.7% of the top figure for beef from Figure 1. [Footnote 2]
MYTH 2: BUYING BEEF FROM LOCAL SOURCES IS ENVIRONMENTALLY-FRIENDLY
Why wouldn’t you believe this one, when the Australian Conservation Foundation says: “And be sure to support hardworking families in your community by buying from local farmers.”
Similarly, Bill McKibben has said that one of the most important measures for reducing the climate change impact of animal agriculture is to buy locally. He has said that when he’s at home, he tries to eat nothing produced outside the valley in which he lives.
But how effective is that approach in terms of beef?
The following image depicts the FAO’s breakdown of emissions from beef production (including beef from dairy cows), with “postfarm” emissions of 0.5 percent (including transport and processing) highlighted.
Figure 2: Breakdown of emissions from beef production (global average)
The main contributors are: enteric fermentation (which produces methane in a cow’s digestive system) 42.6%; manure-related emissions 23.1%; land use change through pasture expansion 14.8%; feed 10%; and fertilizer and crop residues 7.4%.
You can focus as much as you like on locally produced meat, but the relative positive impact is negligible.
Vested interest groups attempt to create the impression that beef and other animal products can be produced in an environmentally benign way. In reality, on the scale required to feed the masses, such products are unsustainable. A general shift towards a plant-based diet, along with a move away from fossil fuels, is essential if we are to overcome catastrophic climate change.
1. I commented on Bill McKibben’s position in my article “Do the math: There are too many cows“.  He appeared to be supporting a key proponent of intensive grazing systems, Allan Savory, on whom I commented in my article “Livestock and Climate: Why Allan Savory is not a saviour“.  Savory’s methods, even if successful in some situations, would never scale up to the level required.
2. Soy beans and other products grown on land that had been cleared of rain forest for that purpose would have a higher emissions intensity figure than indicated here, but still tiny compared to beef. In any event, if such products were only grown for human consumption, we would almost certainly not need to encroach on forested areas in that way. Most soy is grown as part of the grossly and inherently inefficient process of transferring plant-based nutrients to food animals for human consumption.
3. This article first appeared on the website rabble.ca on 15th April, 2014, with the title “Why even grassfed and local beef isn’t sustainable“. This is a slightly expanded version.
4. Postscript 9th May, 2014: The figures in Figure 1 are based on the global average percentage split of the various factors contributing to beef’s emissions intensity. As methane’s percentage contribution would be higher in grazing systems than in mixed systems, the “20-Year GWP” figures may be under-stated for the former and over-stated for the latter. They are intended to be approximations only.
5. Postscript 4th April, 2015: The retail figures attribute all carcass weight emissions to retail cuts of meat. If emissions are also attributed to other products that may be derived from the carcass, utilising fat, bone and the like, then the emissions intensity of the retail cuts will be around 28 percent lower than those shown here. For example, the maximum figure for grazed beef would be around 209, rather than 291 kg CO2-e/kg product.
Author: Paul Mahony
Related articles: Climate Change and Animal Agriculture
Figure 2 adapted from Figure 7, p. 24, Food and Agriculture Organization of the United Nations, “Tackling climate change through livestock: A global assessment of emissions and mitigation opportunities”, Nov 2013, http://www.fao.org/ag/againfo/resources/en/publications/tackling_climate_change/index.htm; http://www.fao.org/docrep/018/i3437e/i3437e.pdf
 Australian Conservation Foundation, Green Home, “Eat less animal products”, http://www2.acfonline.org.au/category/green-eating/tips/eat-less-animal-products (accessed 14 April, 2014)
 McKibben, Bill, “The only way to have a cow”, Orion Magazine, Mar/Apr 2010, http://www.orionmagazine.org/index.php/articles/article/5339/
 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/
 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; http://www.journalofanimalscience.org/content/77/6/1392.full.pdf
 Paterson, J., “CSIRO says cow methane emissions lower than first thought”, ABC Rural, 27 May, 2011, http://www.abc.net.au/site-archive/rural/news/content/201105/s3229224.htm
 Food and Agriculture Organization of the United Nations, “Tackling climate change through livestock: A global assessment of emissions and mitigation opportunities”, Nov 2013, http://www.fao.org/ag/againfo/resources/en/publications/tackling_climate_change/index.htm; http://www.fao.org/docrep/018/i3437e/i3437e.pdf
 Food and Agriculture Organization of the United Nations, “Greenhouse gas emissions from ruminant supply chains: A global life cycle assessment”, Nov 2013, http://www.fao.org/ag/againfo/resources/en/publications/tackling_climate_change/index.htm; http://www.fao.org/docrep/018/i3461e/i3461e.pdf
 United States Department of Agriculture Economic Research Service, Agricultural Handbook No. 697, June, 1992 (website updated 10 September, 2013), “Weights, Measures, and Conversion Factors for Agricultural Commodities and Their Products”, http://www.ers.usda.gov/publications/ah-agricultural-handbook/ah697.aspx#.U0ihR6Ikykw
 Intergovernmental Panel on Climate Change, Fifth Assessment Report, 2014, http://www.ipcc.ch/report/ar5/
 Shindell, D.T., Faluvegi, G., Koch, D.M., Schmidt, G.A., Unger, N., Bauer, S.E., “Improved Attribution of Climate Forcing to Emissions“, Science 30 October 2009: Vol. 326 no. 5953 pp. 716-718 DOI: 10.1126/science.1174760, https://www.sciencemag.org/content/326/5953/716.figures-only
 Intergovernmental Panel on Climate Change, Fifth Assessment Report, 2014, http://www.ipcc.ch/report/ar5/, cited in Romm, J., “More Bad News For Fracking: IPCC Warns Methane Traps More Heat”, The Energy Collective, 7th October, 2013, http://theenergycollective.com/josephromm/284336/more-bad-news-fracking-ipcc-warns-methane-traps-much-more-heat-we-thought
 Hamilton, C, “Scorcher: The Dirty Politics of Climate Change”, (2007) Black Inc Agenda, p. 40
 George Wilkenfeld & Associates Pty Ltd and Energy Strategies, “National Greenhouse Gas Inventory 1990, 1995, 1999, End Use Allocation of Emissions Report to the Australian Greenhouse Office, 2003, Volume 1”, Table S5, p. vii
 Australian Aluminium Council Ltd, “Climate Change: Aluminium Smelting Greenhouse Performance”, http://aluminium.org.au/climate-change/smelting-greenhouse-performance (Accessed 14th April, 2014)
 Turton, H. “Greenhouse gas emissions in industrialised countries Where does Australiastand?”, The Australia Institute, Discussion Paper Number 66, June 2004, ISSN 1322-5421, p. viii, https://www.tai.org.au/documents/dp_fulltext/DP66.pdf
 Carlsson-Kanyama, A. & Gonzalez, A.D. “Potential Contributions of Food Consumption Patterns to Climate Change”, The American Journal of Clinical Nutrition, Vol. 89, No. 5, pp. 1704S-1709S, May 2009, http://www.ajcn.org/cgi/content/abstract/89/5/1704S
 Mahony, P., “Do the math: There are too many cows”, 26 July, 2013, https://terrastendo.net/2013/07/26/do-the-math-there-are-too-many-cows/
 Mahony, P., “Livestock and Climate: Why Allan Savory is not a saviour“, 26 March, 2013, https://terrastendo.net/2013/03/26/livestock-and-climate-why-allan-savory-is-not-a-saviour/