The 3 Percent diet
By Paul Mahony /
Oct 2, 2014

Key climate change problems with livestock

I’ve mentioned previously that the link between livestock production and climate change involves many inter-related factors, including:

  • livestock’s inherent inefficiency as a food source;
  • the massive scale of the industry, including tens of billions of land animals slaughtered annually;
  • land clearing for feed crops and pasture;
  • extensive grazing on open rangelands, with resultant degradation and loss of soil carbon;
  • greenhouse gases such as carbon dioxide, methane and nitrous oxide, along with other warming agents such as black carbon.

In various respects, many official figures under-report livestock’s climate change impacts.  The under-reporting occurs because relevant factors are either: (a) omitted entirely; (b) classified under non-livestock headings; or (c) considered but with conservative calculations.

Greenhouse gas emissions intensity

In my April, 2014 article “Some myths about meat“, I referred to a November, 2013 report by the Food & Agriculture Organization of the United Nations (FAO), showing the emissions intensity of beef and other commodities. [1, 2] Emissions intensity represents the kilograms of greenhouse gas emissions per kilogram of product. The FAO report included some of the factors that are generally not allocated to livestock in official figures, including relevant land clearing.

For figures used in that article, I applied two additional factors, namely: (a) emissions per kilogram of end product (“retail weight”), rather than (as reported) emissions per kilogram of carcass weight; and (b) 20-year “global warming potential” (GWP) for methane, rather than (as reported) the 100-year figure.

I also compared the emissions from livestock to those from an incredibly emissions intensive product, aluminium. Some key points: (a) Aluminium smelting has at times consumed 16 percent of Australia’s electricity generation; (b) That’s particularly significant when you consider that Australia’s economy is the 12th largest in the world; (c) The emissions intensity of Australia’s aluminium smelting is 2.5 times the global average due to the fact that the electricity is primarily derived from coal. [3, 4, 5].

In June, 2014, researchers from Oxford University released their estimates of emissions intensity for a wide range of food products, as shown in Figure 1. The Oxford study was based on information that had previously been provided by around 55,000 participants ranging from high meat eaters to vegans. Consistent with findings elsewhere, the researchers reported that the emissions intensity of plant-based products was far lower than that of the animal-based alternatives. [6]

Figure 1: Greenhouse Gas Emissions Intensity of Food Products Consumed in the UK (Oxford study)


I have used many of the Oxford figures, along with figures from the FAO for beef, chicken and pig meat, to create the comparison outlined in Figure 2.

Figure 2: Greenhouse Gas Emissions Intensity of various commodities


Daily and weekly greenhouse gas emissions

Using the emissions intensity figures referred to above, I have calculated the emissions of some alternative daily food choices. The only difference between those choices are the foods enclosed in borders in Figure 3(a). Calories ranged from around 2,300 (fish-based) to around 2,600 (beef-based). Figure 3(c) shows the weekly emissions based on various combinations.

Figure 3 (a): Alternative food mixes


Figure 3 (b): Daily greenhouse gas emissions of alternative food mixes (identified by key distinguishing ingredient)


Figure 3 (c): Greenhouse gas emissions of alternative food mixes (sample food intake for one week identified by key distinguishing ingredient)


The 3 percent factor

The lowest-emissions choice (plant-based) results in around 3 percent of the emissions of the highest (based on grass-fed beef). Of course, people are unlikely to eat grass-fed beef every day, but the charts highlight the extent to which food choices can affect our overall greenhouse gas emissions.

Could a plant-based diet result in zero dietary emissions?

The person regarded by many as the world’s pre-eminent climate scientist, Dr James Hansen, has reported (with research colleagues) a maximum annual sequestration (absorption) potential of 1.6 gigatonnes of carbon through reforestation. [7] That equates to around 5.9 gigatonnes of carbon dioxide per year. [8] (Global carbon emissions in 2012 were 9.7 gigatonnes, equivalent to 35.6 gigatonnes of carbon dioxide.) [9]

Assuming that all those who currently eat meat converted to a plant-based diet, there would be around 5.8 billion new vegetarians globally, being the current population of around 7.3 billion less an estimated 1.5 billion who are already vegetarian. [10] Assuming that those people’s subsequent dietary greenhouse gas emissions were 2 kg per day on average, in aggregate they would be emitting around 4.2 gigatonnes of greenhouse gases through their diet annually. That is less than the 5.9 gigatonnes sequestered through reforestation, much of which would arise from the general transition to a plant-based diet.

On that basis, the benefit to be derived from those people converting to a plant-based diet, simply in terms of reforestation, may be greater than their ongoing diet-related emissions.

What about chicken and fish?

While emissions from diets featuring chicken and fish are comparable to the plant-based alternative, those two commodities in their own right are around three to four times as emissions intensive. They also involve other massive environmental problems, including destruction of oceanic ecosystems and waste from around 60 billion chickens bred and slaughtered annually.


We face a planetary emergency in the form of climate change, yet the critical issue of diet seems to be effectively ignored by most environmental campaigners. It’s time for those people and others to wake up and address the issue before it’s too late.

Author: Paul Mahony (also on Twitter, Slideshare and Scribd)

Note: This article first appeared on the author's Terrastendo website on 9th September, 2014.


[1] Mahony, P. “Some myths about meat”, Terrastendo, 16th April, 2014,

[2] Food and Agriculture Organization of the United Nations, “Tackling climate change through livestock: A global assessment of emissions and mitigation opportunities”, Nov 2013,;

[3] Hamilton, C, “Scorcher: The Dirty Politics of Climate Change”, (2007) Black Inc Agenda, p. 40

[4] The World Bank, GDP Ranking, 8th May, 2014,

[5] Turton, H. “Greenhouse gas emissions in industrialised countries Where does Australia stand?”, The Australia Institute, Discussion Paper Number 66, June 2004, ISSN 1322-5421, p. viii,

[6] Scarborough, P., Appleby, P.N., Mizdrak, A., Briggs, A.D.M., Travis, R.C., Bradbury, K.E., & Key, T.J., “Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK”, Climatic Change, DOI 10.1007/s10584-014-1169-1,

[7] Hansen, J; Sato, M; Kharecha, P; Beerling, D; Berner, R; Masson-Delmotte, V; Pagani, M; Raymo, M; Royer, D.L.; and Zachos, J.C. “Target Atmospheric CO2: Where Should Humanity Aim?”, 2008, Open Atmos. Sci. J., 2, Supplementary Material, p. xvi, doi:10.2174/1874282300802010217,

[8] IPCC Working Group III: Mitigation, IV Units, Conversion Factors, and GDP Deflators,

[9], Global Carbon Emissions,

[10] Leahy, E., Lyons, S., Tol, R.S.J., “An estimate of the number of vegetarians in the world”, ESRI Working Papers, The Economic and Social Research Institute (ESRI), 2010, and

Image: © Gkuna | Dreamstime.comGrazing Cows Photo

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