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The World’s Leading Driver of Climate Change: Animal Agriculture

Andy Vrbicek suggests that the role of animal agriculture in climate change is vastly underestimated because of calculation parameters in this thought-provoking essay.

Published January 18, 2015 | Updated October 4, 2021 | Andy Vrbicek

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Most reading this article are probably aware of the animal cruelty issues surrounding the livestock industry, the significant contribution to water and air pollution, and the strain on water, land, and energy resources.  But few people likely think of livestock in the context of global warming and climate change.  We should.

It is important that cultured meat proponents are able to refer interested parties to the full breadth of the factory farming industry’s environmental impact—including and especially its significant contribution to climate change and global warming.

In a widely-cited report, Livestock’s Long Shadow (LS), the Food and Agricultural Organization (FAO) posited the livestock industry contributes 18% of the world’s greenhouse gas (GHG) emissions.1  Conversely, in Livestock and Climate Change (LCC), environmental assessment experts at the World Bank found the industry is actually responsible for a staggering 51% of global GHG emissions.2  By way of comparison, even 18% is more than the entire transportation sector’s emissions.3  But which figure is more accurate?

Getting to the Meat of the Matter: The Livestock Industry & Greenhouse Gas Emissions

This article reveals how the FAO obfuscates and trivializes livestock’s impact on global warming, and why the industry almost certainly does account for half the world’s climate change-driving GHG emissions.  As an initial matter, it is worth noting the widely disparate World Bank and FAO estimates do not represent a mere “he said she said” or proper “battle of the experts”—the World Bank authors of LCC are both environmental assessment experts, while not a single FAO author of LS is an environmental assessment expert.4 This of course violates international environmental assessment best practices for projects which have a significant environmental impact (like global livestock and feed production).5 In fact, for committing an “elementary error” in environmental assessment, a portion of LS was forced to be retracted.6  Defenses of the FAO’s report in light of the World Bank’s 51% figure have been shoddy and only furthered skepticism towards FAO estimates.7

Missing Animals

In LCC, the World Bank posited that there were some 50 billion livestock animals worldwide, while the FAO in LS used a figure of only 21.7 billion (despite the fact other reports from within the FAO itself had suggested the number was much higher, and other governmental agencies had estimated the number at around 50 billion).8  Soon after publication of LS, the FAO effectively conceded 21.7 billion was erroneous when their own website listed the number at 56 billion—a figure 258% greater than used in LS, and 10% greater than used in LCC.9 More recent estimates suggest the planet currently homes 70 billion livestock animals.10

As a brief aside, global meat demands are only rising.  A 2013 FAO report suggests livestock demand is expected to increase 70% by 2050.11 Yet, the FAO does not address alternative means of satisfying growing protein needs—and thus eschews an essential task of environmental impact assessments, the consideration of alternatives—but only recommends greater livestock intensity.12 The FAO does suggest the livestock sector can potentially curb GHG emissions by 30% through better practices and technology, but this claim is dubious given livestock specialists have typically only found room for a 10% reduction.13 The World Bank authors in LCC, on the other hand, do acknowledge the obvious need to reduce our unsustainable livestock populations and do discusses the prospects of alternative protein sources.

Livestock Respiration

Beyond grossly undercounting livestock populations, further accounting for the wide discrepancy between the reports, the FAO did not count CO2 from animal respiration, whereas the World Bank did.  Yet, according to the Kyoto Protocol livestock respiration should be counted.14 And there is good reason for it: “Livestock [like automobiles] are a human invention and convenience, not part of pre-human times, and a molecule of CO2 exhaled by livestock is no more natural than one from an auto tailpipe… Today, tens of billions more livestock are exhaling CO2 than in pre-industrial days….”15

Methane and Global Warming Potential Timeframes

Finally, the FAO used a “global warming potential” (GWP) value for methane per a 100-year timeframe, whereas the World Bank used a 20-year timeframe.   For the purpose of counting GHG emission, each greenhouse gas is assigned a GWP value according to its capacity to warm the planet relative to an equivalent amount of CO2 over a given period of time.  Methane is an extremely potent GHG gas: Per figures used in LS and LCC respectively, ton for ton methane contributes to global warming 23 times more than CO2 when viewed over a 100-year timeframe, and 72 times more over a 20-year timeframe (methane’s GWP diminishes over time relative to CO2 because methane stays in the atmosphere for only 12 years, whereas CO2 lingers for over 100).

Importantly, after publication of both LS and LCC, the Intergovernmental Panel on Climate Change (IPCC) adjusted methane’s GWP values over a 10-, 20-, and 100-timeline, to 108, 86, and 34 respectively.16  Others give values even higher still.17 Thus, for using outdated GWP values for methane, both LS and LCC estimates of the livestock’s contribution to global warming are conservative in this respect.

Tipping Points, Feedback Loops & Why GWP Timeframes Matter

Most projections of climate change presume that future changes—greenhouse gas emissions, temperature increases and effects such as sea level rise—will happen incrementally.  A given amount of emission will lead to a given amount of temperature increase that will lead to a given amount of smooth incremental sea level rise. But pushing global temperatures past certain thresholds could trigger abrupt, unpredictable and potentially irreversible changes that have massively disruptive and large-scale impacts.18

Because the livestock industry is the world’s leading emitter of methane—with 44% of the industry’s total GHG emissions in the form of methane19—which GWP timeframe is used is important. One hundred-year timeframes, such as used by the FAO, are problematic. The IPCC states this on the matter: “There is no scientific argument for selecting 100 years compared with other choices.  The choice of time horizon is a value judgment since it depends on the relative weight assigned to effects at different times.”20  Yet, the IPCC’s equivocality here is unfortunate and ignores compelling reasons why a 20-year (or shorter) timeframe is a far more relevant metric.

The International Energy Agency has suggested that unless drastic reductions are immediately achieved, atmospheric GHG’s could reach levels which will inevitably result in irreversible catastrophic climate change.21  Thus, as many scientists have recommended,22 environmental assessment experts should use 10- or 20-year GWP timeframes, as policy makers must be primarily focused on the coming decade or two, opposed to the coming century.23 Modest warming over the coming decades could trigger runaway feedback loops, catastrophic tipping points leading to exponential warming. For instance, as temperatures rise and melt permafrost and methane clathrates, more methane is released causing accelerated warming, which in turn causes more melting and methane release, which in turn causes further accelerated warming, and so on and so forth.24 Thus 100-year timeframes are largely irrelevant for failing to reflect the urgency of the matter and the immediate need for significant reductions in potent GHG’s like methane. Indeed, viewed under a 10-year timeframe, methane is seen as the world’s leading driver of global warming, greater even than CO2.25

A Glimmer of Hope: The Livestock Industry, A Unique Opportunity to Mitigate Global Warming

There is something of a silver lining. Recall that methane only stays in the atmosphere for 12 years. For this reason—and because of methane’s monstrous GWP and the sheer volume of current emission levels—methane and the livestock industry represent a unique opportunity, and among our only hope, for mitigating runaway global warming.26  Thanks to methane’s short half-life, through swift and drastic emission reductions we can relatively quickly undo significant amounts of damage, and potentially stave off dramatic climate change tipping points.

Additionally, whereas most industries can only achieve significant GHG emission reductions through a switch to renewable energy (which will necessitate some 20 years and $18 trillion dollars for the development of sufficient infrastructure), the livestock industry is unique in that most of its emissions do not come from energy use but from biological processes.27

Thus, while enormous obstacles stand in the way of widespread implementation of renewable energies, significant reductions in livestock populations on the other hand can be accomplished with relative ease (made all the easier by forthcoming meat replacement technologies).  And, with the industry as the world’s leading methane and total GHG emitter, reductions here would have a greater (and, importantly, quicker) positive environmental impact. For these reasons, the immediate focus of climate change mitigation efforts should be shifted away from cars and coal and squarely onto cows and methane.

While governments continue to struggle to agree on measures that would increase renewable energy infrastructure significantly, alternatives to livestock products could be scaled up quickly to reduce today’s grave risk of climate change significantly. Indeed, reducing animal feed  production and replacing at least one quarter of today’s livestock products with substitutes could be the only way for governments, industry, and the general public collaboratively to take to take a single, powerful action to reduce climate change quickly.28


Animal cruelty issues certainly offer an extremely compelling reason to oppose factory farming.  But livestock’s contribution to global warming likely represents the most forceful argument for lawmakers to take decisive action against the industry.  For the reasons outlined herein, New Harvest and other cultured meat proponents – environmentalists, and animal welfare-ists – should be emboldened to use the World Bank estimate that the livestock industry is responsible for half of the world’s global greenhouse gas emissions.  Indeed, for using an outdated GWP value for methane—and because livestock populations are only increasing—51% is likely conservative.

Armed with the burgeoning technology of cultured meat to help strengthen the political resolve, activists ought to implore law and policy makers to enact sweeping legislation and regulation designed to dramatically curtail patently unsustainable livestock populations.  To be sure, there is no other feasible, singular action that can do more to mitigate global warming and climate change.



[1] FAO, 2006. Livestock’s Long Shadow: Environmental Issues and Options. Food and Agriculture Organization of the United Nations.
[2] Goodland, R. and Anhang, J., “Livestock and Climate Change: What if the key actors in climate change were pigs, chickens and cows?” (2009). Worldwatch November/December 2009, Worldwatch Institute, pp. 10–19.
[3] See EPA, Global Green House Gas Emissions.
[4] Goodland, R. and Anhang, J. “Response to ‘Livestock and greenhouse gas emissions: The importance of getting the numbers right’” (2011).
[5] Ibid.
[6] Ibid.
[7] See M. Hererro et al., “Livestock and greenhouse gas emissions: The importance of getting the numbers right,” (2011). Animal Feed Science and Technology. See also Goodland 2011, note 4.  In one of the lone published challenges to LCC, Hererro et al. mischaracterized certain positions taken by the World Bank authors, made other misleading comments and factual inaccuracies, and curiously defended an instance of FAO’s departure from the most widely accepted GHG counting protocol.  Ibid. Moreover, Hererro et al. falsely stated LCC had not been subject to peer review, while it is unlikely that LS was peer reviewed.  See “Livestock and Climate: Whose Numbers are More Credible.” Rounding out the controversy—in their paper which effectively argued LS is the singular definitive authority on the livestock industry’s contribution to global GHG emissions—Hererro et al. failed to mention under their “Conflict of Interest” heading that their paper was authored by both a co-author and the lead author of LS. Goodland 2011, note 4.
[8] Goodland 2009, note 2.
[9] Keith Akers “Scaling up the Methane emissions for Livestock?
[10] Compassion in World Farming, “2013-2017 Strategic Plan for Kinder, Fairer, Farming Worldwide” (2013).
[11] Food and Agriculture Organization (FAO) “Tackling climate change through livestock…” (2013).  Despite accounting for some two and a half times more livestock than in LS, curiously and without explanation, this 2013 FAO report dialed down livestock’s percentage of global GHG emissions from 18% to 14.5%. One can speculate whether this represents the influence of Frank Mitloehner, who was sitting chair of the FAO’s livestock environmental assessment committee, and who had become known for publicly challenging the LS’s figure of 18% as too high.  See   Before he was given his FAO chair position, Mitloehner published a paper pegging livestock’s percentage of GHG emissions in America at a modest 3%. Tellingly, this report was funded by the Beef Checkoff Program. Ibid.  The Beef Checkoff Program is a “producer-funded marketing and research program designed to increase domestic and/or international demand for beef…The fundamental goal of every checkoff program is to increase commodity demand, thereby increasing the potential long-term economic growth of all sectors of the industry.”
[12] FAO 2013, note 11.
[13] A. Petherick. A. “Light is cast on a long shadow” (2012). Nature Climate Change 2: 705-706.
[14] Goodland 2009, note 2.
[15] Ibid.
[16] Intergovernmental Panel on Climate Change, CLIMATE CHANGE 2013: THE PHYSICAL SCIENCE BASIS. (2013).
[17] See e.g. Robert W. Howarth, “A bridge to nowhere: methane emissions and the greenhouse gas footprint of natural gas” (2014) (citing three studies finding methane has a GWP value of 105 over a 20-year timeframe).
[18] American Association for the Advancement of Science “What We Know: The Reality, Risks and Response to Climate Change” (2014).
[19] Cows are the primary culprit here.  Through manure and enteric fermentation (digestive processes in ruminant animals which produce methane and is released via belching and flatulence), cows release vast amounts of methane.  The figure 44% comes from the FAO in their LS report; it is unclear what this number would be per the World Bank’s LCC report.
[20] IPCC 2013, note 16.
[21] International Energy Agency, “World Energy Outlook,” 2011.
[22] See e.g., Dyer et al.  “The Protein-based GHG Emission Intensity for Livestock Products in Canada,” (2010). Journal of Sustainable Agriculture, 34: 6, 618 — 629 (noting four scientists at Canada’s government agency Agricultural and Agri-Foods Canada recommend 20-year timeframes).
[23] See Howarth 2014, note 17. “An increasing body of science is developing rapidly that emphasizes the need to consider methane’s influence over the decadal timescale, and the need to reduce methane emissions. Unfortunately, some recent guidance for life cycle assessments specify only the 100-year time frame, and the EPA in 2014 still uses the GWP values from the IPCC 1996 assessment and only considers the 100-year time period when assessing methane emissions. In doing so, they underestimate the global warming significance of methane by 1.6-fold compared to more recent values for the 100-year time frame and by four to fivefold compared to the 10- to 20-year timeframes”
[24] See e.g., ibid.
[25] IPCC 2013, note 16.
[26] “The model…adopted by the United Nations predicts that unless emissions of methane and black carbon are reduced immediately, the Earth’s average surface temperature will warm by 1.5°C by about 2030 and by 2.0 degrees 2.0°C by 2045 to 2050 whether or not carbon dioxide emissions are reduced.”
[27] Robert Goodland, “Happier Meals,” 2014.
[28] Goodland 2011, note 4.

About the Authors
Andy Vrbicek is a JD candidate at Sandra Day O’Connor College of Law at Arizona State University. His primary legal interests include greenhouse gas and factory farm regulation. Andy is happy to field questions and comments at