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Animal agriculture is responsible for 18 percent of greenhouse gas emissions, more than all transportation combined.

By http://www.cowspiracy.com/facts/ from Fao.org. Spotlight: Livestock impacts on the environment.

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  • Explanation: That link has been thrown about a lot in pro-vegan discussions... so I am picking three of their more juicy claims more or less randomly to see how they fare. Nov 27 '14 at 18:10
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    Note that there is significant overlap between animal agriculture and transportation. Do trucks with animals count to animal agriculture emission? Do trucks with meat or dairy do?
    – gerrit
    Nov 27 '14 at 20:29
  • Without Hot Air goes into quite a lot of detail on pretty much everything energy and greenhouse-gas related. It's not a gripping read but is very informative and seems very unbiased. See Chapter 13: Food and farming
    – Basic
    Nov 28 '14 at 2:01
  • @DavidMulder See for yourself, there are moderators around here who delete anything that isn't a link. Writing on this site is a waste of time. Nov 28 '14 at 22:25
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    That does'nt however imply that going vegan improves the situation. If dont just look at the kg CO2/kg product numbers but instead divide by the nutritional factor to get g CO2/kCal things look different. Chicken~lettuce, pork~tomatos, tomatos from green houses actually worse than beef. Duh. Sep 19 '19 at 17:13
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Yes. In fact, some sources calculate that the Food and Agriculture Organization of the United Nations (FAO) figure is actually an underestimate.

A frequently cited study on the topic is Steinfeld et al. (2006). This is the FAO study already mention in the question. It has 5600 citations on Google Scholar, although only 40 in the more conservative Scopus. I am not sure if it is peer-reviewed.

To judge its quality, we could look at what other scientific studies have to say about it. To pick one, here it is summarised by Koneswaran et al. (2008):

Although much evidence has been amassed on the negative impacts of animal agricultural production on environmental integrity, community sustainability, public health, and animal welfare, the global impacts of this sector have remained largely underestimated and underappreciated. In a recent review of the relevant data, Steinfeld et al. (2006) calculated the sector’s contributions to global greenhouse gas (GHG) emissions and determined them to be so significant that—measured in carbon dioxide equivalent—the emissions from the animal agricultural sector surpass those of the transportation sector.

The FAO report is also cited by the IPCC AR WG3 report.

A more recent study by Goodland and Anhang (not peer reviewed, but cited by at least 19 Scopus-indexed studies) claims that the FAO study actually underestimates livestock's contribution:

A widely cited 2006 report by the United Nations Food and Agriculture Organization, Livestock's Long Shadow, estimates that 18 percent of annual worldwide GHG emissions are attributable to cattle, buffalo, sheep, goats, camels, pigs, and poultry. But recent analysis by Goodland and Anhang finds that livestock and their byproducts actually account for at least 32.6 billion tons of carbon dioxide per year, or 51 percent of annual worldwide GHG emissions.

See also this article in The Independent which discusses the Goodland and Anhang paper. A further study is by Garnett (2011) (emphasis mine):

While there are no studies that quantify GHG emissions arising from the entire global food chain, there have been estimates of GHGs attributable to global agricultural production. The IPCC estimates agriculture’s direct impacts to stand at about 10–12% of global emissions (5100–6100 MTCO2 eq); this excludes emissions resulting from fuel use, fertiliser production and agriculturally induced land use change (Smith et al., 2007).

The figure rises to up to 30% when additional emissions from fuel use, fertiliser production and agriculturally induced land use change are included; land use change alone accounts for 6–17% (Bellarby et al., 2008).

One regional analysis for Europe finds that food accounts for 31% of the EU-25’s total GHG impacts, with a further 9% arising from the hotel and restaurants sector (European Commission, 2006). At the national level, developed country studies find food consumption contributes between 15% and 28% to overall national emissions (Garnett, 2008, Defra, 2009, Audsley et al., 2010, Swedish Environment Protection Agency, 2010, Regional Activity Centre for Cleaner Production, 2008, Nieberg, 2009, Kim and Neff, 2009 and Consuming Australia, 2007). Fig. 2 shows the breakdown of emissions at each stage in the supply chain for the UK food system. One UK study (Audsley et al., 2010) additionally quantifies emissions associated with food consumption-induced land use change and finds that this increases the food chain’s overall GHG contribution by 66%.

However, the Garnett paper considers both animal and non-animal agriculture, so these figures cannot be directly compared. However, they go on to state:

Since livestock utilise around 80% of the world’s agricultural land (FAO, 2009) and generate the bulk of the sector’s GHGs, there is a perception that efforts to raise livestock yields can generate both environmental and commercial benefits.

In summary: exact methodologies differ and it can be difficult to compare figures, a literature survey did not show significant disagreement with the FAO study. Do trucks with animals count as animal agriculture? Do trucks with meat?

Studies that I found that disagreed rather considered that the FAO underestimated animal-agriculture-induced emissions, than that they overestimated it. So: Yes, animal agriculture is responsible for more greenhouse gas emissions than transportation.

  • Steinfeld H, Gerber P, Wassenaar T, Castel V, Rosales M, de Haan C. Livestock’s Long Shadow: Environmental Issues and Options. Rome: Food and Agriculture Organization of the United Nations; 2006.

  • Koneswaran, G., & Nierenberg, D. (2008). Global Farm Animal Production and Global Warming: Impacting and Mitigating Climate Change. Environmental Health Perspectives, 116(5), 578–582. doi:10.1289/ehp.11034

  • Robert Goodland and Jeff Anhang. Livestock and Climate Change, World Watch Magazine, November/December, Volume 22, No. 6. Online PDF

  • Tera Garnett. Where are the best opportunities for reducing greenhouse gas emissions in the food system (including the food chain)? In: Food Policy, Volume 36, Supplement 1, January 2011, Pages S23–S32, doi:10.1016/j.foodpol.2010.10.010


P.S. Note that when people say emissions, they often mean net emissions, i.e. total sources minus total sinks. As the two are constantly in flux, total emission as such is not very meaningful (and quite hard to determine).

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    How much of this is due to the animals' breathing/flatulence as opposed to machines?
    – isarandi
    Nov 28 '14 at 0:51
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    @Mazura Forests are a CO₂ sink. Removing the sink leads to an increase in atmospheric CO₂.
    – gerrit
    Nov 28 '14 at 16:29
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    @Mazura It leads to more net emissions. There are continuously very large amounts of emissions and very large amounts of sinking. The total amount of emission is not relevant (and hard to determine). What is relevant is the net. So, whereas less sinking does not lead to more emissions, it does lead to more net emissions, which is what is relevant.
    – gerrit
    Nov 28 '14 at 19:12
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    @Mazura if you cut down the forest, the carbon that had been stored in the trees will be released by either burning the trees or the decay of the wood all in one go. As I understand it mature forests are not actually much of a carbon sink because when they reach steady state the primary production (addition of material to the trees) is mostly balanced by the decay of the trees that have died naturally. Information and data on land use change emissions is available here cdiac.ornl.gov/trends/landuse/houghton/houghton.html see cited papers for explanations etc.
    – user18604
    Nov 29 '14 at 10:49
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    @DocSalvager A fraction of the equivalent produced for meat (10-20% IIRC). We need significantly less land to grow crops to feed humans with vegetables than to feed humans with meat. Beef is very bad. Chicken is less bad.
    – gerrit
    Dec 1 '14 at 20:41
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The data is different for just the US:

The primary sources of greenhouse gas emissions in the United States are:

Transportation (28.9 percent of 2017 greenhouse gas emissions) – The transportation sector generates the largest share of greenhouse gas emissions. Greenhouse gas emissions from transportation primarily come from burning fossil fuel for our cars, trucks, ships, trains, and planes. Over 90 percent of the fuel used for transportation is petroleum based, which includes primarily gasoline and diesel.

Agriculture (9.0 percent of 2017 greenhouse gas emissions) – Greenhouse gas emissions from agriculture come from livestock such as cows, agricultural soils, and rice production.

EPA.gov: Sources of Greenhouse Gas Emissions


Although, I suppose arguing for veganism, it really doesn't need to be confined to the US. The estimate for the world works: 11-50%.

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    Those are numbers about the US, not the world. Sep 19 '19 at 7:35
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Probably yes, but the comparison is fraught with challenges.

Geographical Scope

Selection of geographical area for analysis is the largest confounding factor here. Some areas of the world have more cars, while others have more livestock (especially ruminants, cows) so it's easy to arrive at different answers depending on where you look. For example, Uruguay has more cattle than humans, so livestock will have a relatively large effect on the GHG inventory of Uruguay. On the other hand, San Marino has more cars than people, so transportation will have a relatively large effect on their GHG emissions.

Because climate change is a global issue, it's tempting to compare transportation vs. livestock on a global basis. However, that comparison isn't very useful for understanding what changes need to be made at a country, state, or personal scope.

This is further complicated because some measurements (CO2 from tailpipes and CH4 from enteric fermentation) are easily attributed to a specific geographic area, while indirect scope 3 emissions are difficult to assign to a specific area. Look at "Point-of-release vs. Lifecycle Analysis" below where I explain this in more detail.

Different Gases

Transportation is mostly associated with releasing CO2 (carbon dioxide) while livestock are mainly associated with releasing CH4 (methane). These gases behave differently in the atmosphere; CH4 has an initially large effect that subsides over a few decades, while CO2 has a smaller effect that adds up over centuries. Climate scientists introduced Global Warming Potential (GWP) which looks at the impact over a fixed period of time, typically 100 years, in an attempt to simplify the comparison of different gases.

Global warming is occurring rapidly, so we need fast-acting solutions, and that's one reason to put more emphasis on methane (and livestock) reductions right now.

Point-of-release vs. Lifecycle Analysis

Cars emit CO2 as a byproduct of gasoline combustion. This is what we call point-of-release emissions (or "tailpipe" emissions); these are relatively simple to measure and regulate. However, there was a long chain of activities required in order to get that gasoline in the tank.

  • A gasoline transport truck had to drive to the gas station, and that truck emitted CO2.
  • A fuel refinery had to process raw crude into usable gasoline, and that required a lot of energy, and CO2 was likely emitted while producing that energy.
  • The fuel refinery probably burned some unwanted products in a gas flare which also released CO2 into the atmosphere.
  • The oil may have been transported in an oil tanker, which also burned fuel, which also released CO2.

All of these activities release greenhouse gases, but they're hard to measure and allocate, so they're often left out of the comparison.

Livestock, especially cattle and other ruminants, produce CH4 in their stomachs in a process called enteric fermentation and that is released when they belch. These point-of-release emissions are relatively simple to measure and regulate. However, a long chain of activities is required to support the growing (and eventual slaughter and processing) of that cow.

  • Water is pumped from rivers and underground aquifers and used to irrigate crops.
  • Fertilizer is produced via the Haber process which often uses fossil fuels.
  • Forest land is cleared (especially in Brazil's Amazonian rainforest) to make room for grazing cattle. The trees and soil decompose and release CH4 and CO2 into the atmosphere.
  • Manure releases several kinds of greenhouse gases.

All of these activities release greenhouse gases, but they're hard to measure and allocate, so they're often left out of the comparison.

Deforestation has a massive impact on carbon emissions, and when deforestation is included as part of the long carbon footprint of livestock, it usually results in livestock being attributed to releasing more greenhouse gases than transportation.

The Carbon Cycle

Some people will tell you that livestock are carbon neutral because they exist as a natural part of the carbon cycle but there are three main fallacies associated with that claim.

  1. Some livestock, especially cattle and other ruminants, convert large amounts of carbon into CH4, thanks to enteric fermentation. This temporarily "upgrades" the carbon into a much more potent greenhouse gas for a few decades. If this CH4 was immediately combusted, it would have less impact on climate change. In fact, some dairy farms are trying to do exactly that! (see: dairy digesters).
  2. The increasing global population demands more animal products, which requires more land, which results in permanent deforestation, which is not part of the natural carbon cycle. Deforestation and soil degradation is a major contributor to climate change.
  3. Some of the inputs to animal agriculture, such as fertilizer produced using the Haber process, are currently dependent on use of fossil fuels. This is not a natural part of the carbon cycle.
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    Nice first answer Nick. Welcome to Skeptics, enjoy the site. Aug 31 at 21:07
  • For the things that aren't typically counted along with transportation and livestock emissions, do you have an estimate of how they factor? I've always assumed such things are probably 1% or less of the total emissions, excluding land-use change.
    – LShaver
    Aug 31 at 22:33

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