Does Cattle Livestock Contribute 51% of Human-Derived Greenhouse Gas Emissions?

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

Check out this answer from Consensus:

The claim that cattle livestock contributes 51% of human-derived GHG emissions is not supported by the majority of scientific research. Most reliable estimates place the contribution of livestock, including cattle, at around 10-18% of global GHG emissions. While cattle are a significant source of methane and other GHGs, attributing more than half of human-derived emissions to them is an overestimation. Therefore, it is crucial to rely on scientifically robust and widely accepted estimates to inform policy and mitigation strategies.

The role of cattle livestock in contributing to human-derived greenhouse gas (GHG) emissions has been a topic of significant debate and research. Various studies have attempted to quantify the exact contribution of livestock to global GHG emissions, with some estimates suggesting a wide range. This article aims to explore whether cattle livestock contributes 51% of human-derived GHG emissions by reviewing the findings from multiple research papers.

Contribution of Livestock to GHG Emissions

Global Estimates

Several studies have provided estimates of the contribution of livestock to global GHG emissions. According to one study, livestock directly contributes about 10-12% of current global anthropogenic GHG emissions, mostly from methane (CH4) and nitrous oxide (N2O) emissions1. Another study estimates that animal agriculture is responsible for 8-10.8% of global GHG emissions, with lifecycle analysis suggesting that livestock could contribute up to 18% of global emissions2.

Regional Variations

The contribution of livestock to GHG emissions varies significantly by region. For instance, in the European Union, livestock production accounts for 12-17% of total GHG emissions3. In the UK, livestock contributes about 9% of national GHG emissions4. These regional variations highlight the complexity of attributing a single global percentage to livestock emissions.

Specific Contributions from Cattle

Cattle are a significant source of livestock-related GHG emissions. One study found that emissions from cattle dominate the livestock sector, particularly in regions like Asia, Latin America, and Africa2. Another study estimated that methane emissions from ruminant livestock, including cattle, accounted for 47-54% of all non-CO2 GHG emissions from the agricultural sector in 20147.

Misconceptions and Clarifications

The 51% Estimate

A controversial estimate suggested that livestock could contribute as much as 51% of global GHG emissions. However, this figure is not widely accepted in the scientific community. A review paper emphasized that estimates of global GHG emissions attributable to livestock range from 8 to 51%, with the higher estimates often arising from deviations from internationally accepted protocols6. These deviations include different methods of accounting for land use changes and the global warming potential of methane.

Reliable Estimates

More reliable estimates from international scientific organizations like the IPCC and FAO suggest that livestock contributes around 14.5% of total annual anthropogenic GHG emissions globally8 9. These estimates are based on comprehensive lifecycle analyses and are widely accepted in the scientific community.

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

David Griffith has answered Unlikely

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

Richard Eckard has answered Extremely Unlikely

An expert from University of Melbourne in Agricultural Science, Environmental Science

According to the IPCC, agriculture contributes an estimated 14% of global anthropogenic greenhouse gas emissions. This figure accounts for emissions of direct methane, nitrous oxide and a small amount of carbon dioxide emissions only. Based on this, the livestock sector is estimated to directly contribute approximately 9 to 11% of total global anthropogenic greenhouse gas emissions.

If we then add the indirect emissions from the livestock sector, which include land-clearing, processing and transport emissions, the total contributions for the sector increase to around 18 to 22%. Livestock’s Long Shadow (FAO 2006) applied a Life Cycle Analysis which included ‘indirect emissions’ associated with livestock production: chemical fertilizer production, deforestation for pasture and feed crops, cultivation of feed crops, feed transport and soil organic matter losses in pastures and feed crops, animal production (e.g. enteric fermentation, and methane and nitrous oxide emissions from manure) and transportation of animal products. Following this analysis, the report estimated that livestock contributes approximately 9% of direct total anthropogenic carbon dioxide emissions, 37% of methane and 65% of nitrous oxide emissions, making a total contribution of 18% of global anthropogenic greenhouse gas emissions.

The figures above are still, however, heavily contested. Irrespective of whether the emission are livestock based, much of the chemical fertilizer production, deforestation, cultivation, transport and soil organic matter losses would occur regardless as we increase crop production to replace these animal products. If we discount these ‘displacement emissions’ (technically referred to as emissions leakage), we revert to more realistic contributions, somewhere between the 14% and 18% estimates.

Higher figures than these are quoted elsewhere, but these are mathematically impossible (and perhaps disingenuous), if you stop to really consider them logically: 1) we know how much carbon dioxide the direct combustion of fossil fuels emits into the atmosphere, and 2) we know how much warming can be attributed to this. Even if we include some provision for the ‘indirect emissions’ associated with livestock production and make an honest discount for ‘displacement emissions’ (to grow, process and transport the equivalent volume of food), the livestock sector plus it’s ‘indirect emissions’ cannot account for any more than one fifth of the observed warming or total measured change, in the atmosphere.

The above does not by any means discount the severity of the problem –a quarter of global anthropogenic greenhouse gas emissions from one food sector is highly significant and requires resolution. Diet moderation is highly recommended for many good reasons, including reducing your personal greenhouse gas footprint and your personal health. However, given how integrated livestock are to many cultures and regions and that livestock are the only realistic option to provide food from arid rangeland systems, the ultimate solution lies in research to deliver a low methane producing ruminant. 

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

Alan DeRamus has answered Unlikely

An expert from University of Louisiana in Agricultural Science, Agrology, Environmental Science

Methane is a potent greenhouse gas whose atmospheric abundance has grown 2.5-fold over the last three centuries, due in large part to agricultural expansion. The farming of ruminant livestock, which generate and emit methane during digestion (‘enteric fermentation’), is a leading contributor to this growth, but not nearly the over 50% that some environments claim.

Our research in Louisiana measured methane in grazing management studies to demonstrate methods for improving beef production per unit of methane emission, and to measure the productivity of beef cattle grazing different adapted forages under traditional and improved management systems. We used the sulfur (SF6) tracer technique to determine the effects of best management practices (BMP) grazing compared with continuous grazing on CH4 production in several Louisiana forages. We found that the projected CH 4 annual emissions in cows showed a 22% reduction from Management Intensive Grazing when compared with continuous grazing (DeRamus, Methane Emissions of Beef Cattle on Forages, 2003).

Numerous reviews over the past decade show that all livestock production account for only 12-20% of the global methane production.

Gill, et al. (2009) in their publication “Mitigating climate change: the role of domestic livestock” reported that Livestock contribute directly (i.e. as methane and nitrous oxide (N2O)) to about 9% of global anthropogenic greenhouse gas (GHG) emissions and around 3% of UK emissions. If all parts of the livestock production lifecycle are included (fossil fuels used to produce mineral fertilizers used in feed production and N2O emissions from fertilizer use; methane release from the breakdown of fertilizers and from animal manure; land-use changes for feed production and for grazing; land degradation; fossil fuel use during feed and animal production; fossil fuel use in production and transport of processed and refrigerated animal products), livestock are estimated to account for 18% of global anthropogenic emissions.

Reviews conducted by the United States Environmental Protection Agency (USEPA) (2005) and for the IPCC by Smith et al. (2007a, 2007b and 2008) show that globally, agriculture (livestock and crop production) accounted for 12% of human-induced GHG emissions in 2005 (Smith et al., 2007a).

K.R. Lassey published in Agricultural and Forest Meteorology (2007) that “The global enteric source of methane from livestock assessed at 80 Tg per year (uncertainty 65–100 Tg per year), contributes 20–25% of the observed 2.5-fold growth in atmospheric methane.”

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

Jan Dijkstra has answered Extremely Unlikely

An expert from Wageningen University and Research Centre in 

This suggested contribution of 51% is not just cattle livestock, but all livestock (including sheep, pigs, poultry, etc). The basis of this claim is a 2009 report of the Worldwatch Institute (WwI) (http://www.worldwatch.org/files/pdf/Livestock%20and%20Climate%20Change.pdf). This report challenges the (now somewhat outdated) estimate of FAO in 2006, that livestock contribute 18% of anthropogenic global greenhouse gas emissions (http://www.fao.org/docrep/010/a0701e/a0701e00.HTM). The WwI report make many erroneous calculations to increase the contribution from 18% to 51%, including the following aspects.

Firstly, unlike IPCC guidelines, CO2 from livestock respiration is included by WwI. In these IPCC guidelines, CO2 from livestock respiration is not considered a net source of CO2, because this CO2 is considered to be part of a rapid biological system. In this system, plant material consumed by the animals is created by photosynthesis, sequestering CO2 in the process. Regardless, if livestock respiration is accounted for, then respiration of men and pets should also be included in the non-livestock related human-derived GHG emissions for consistency, as well as CO2 absorption related to the growth of plants used for feed.

Secondly, WwI argue that livestock related land use and land use change (LULUC) emissions are vastly underestimated. Although methodologies and figures on LULUC may differ greatly, these authors assume higher CO2 emissions related to livestock induced LULUC only. The report ignores other key drivers of LULUC including logging, development of renewable energy, and infrastructure development. Thus livestock contribution is patently overestimated.

Thirdly, the authors of the WwI report adopted a 20-year rather than 100-year time horizon and corresponding global warming potential (GWP) values (at that time, GWP based on IPCC Fourth Assessment Report – AR4). Whilst this is subject to scientific debate, these authors only increased CH4 emissions of livestock, using a GWP raised from 25 (100-year horizon) to 72 (20-year horizon). Authors failed to make a similar correction to non-livestock related CH4 emissions, although a molecule of CH4 from livestock fundamentally does not differ from a molecule of CH4 from other sources. Also, for consistency, authors should have reduced N2O emissions by applying a GWP of 289 rather than 298.           

Finally, the WwI report assumes higher figures of tonnage of livestock products and a 12% livestock related GHG emission rise from 2002 to 2009, compared with the FAO report. They fail to specify their data sources, ignore the fact that higher production levels may coincide with increased efficiency and reduced GHG per unit product, and neglect growth in GHG emissions unrelated to livestock, including increased fossil fuel use.

The contribution of livestock to GHG emissions may be difficult to assess. A sound scientific process is required to make proper estimates. The calculations in the WwI report are inherently flawed, and the report should be left unimplemented by policy makers. Unfortunately, the flawed estimate of 51% has already made some impact on public opinion. According to the latest FAO study, the livestock sector contributes 14.5% to human-induced greenhouse gas emissions (http://www.fao.org/ag/againfo/resources/en/publications/tackling_climate_change/index.htm).

Does cattle livestock contribute 51% of human-derived greenhouse gas emissions?

Richard Todd has answered Extremely Unlikely

An expert from United States Department of Agriculture, Agricultural Research Service in Environmental Science

To clarify, I will report annual greenhouse gas (GHG) emissions in Gt of CO2 equivalents (CO2eq). This means emissions of non-CO2 GHG, like methane, are multiplied by their global warming potential to account for their effectiveness as a GHG relative to CO2. The claim, in these units, then becomes at least 32 Gt of CO2eq.

If you think of the contribution of a particular source or sector to GHG emissions as a box, then the size of that contribution will depend on what we put in the box. For example, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2014) has an emissions sector called Agriculture, Forestry and Other Land Use, which includes the contribution of cattle along with all other agricultural activities. The IPCC estimated that in 2010 this entire sector contributed from 10 to 12 Gt CO2eq of the total 49±4.5 Gt CO2eq of global GHG emissions. In terms of direct emissions of methane, cattle are most likely responsible for about 4% of total global GHG emissions.

The claim of at least 32 Gt CO2eq is based on a single non-peer-reviewed article by Goodland and Anhang (2009) put out by World Watch Institute. They decided to include several sources in their box that are dubious. For example, they included respiratory CO2 from livestock. This is inappropriate because there is no net gain of CO2 when it cycles in one season from atmosphere to plant to animal to atmosphere. Another claim was that grazing land and crop land used for cattle could cut coal use in half if used to directly grow human food and biofuels. The impracticality of such a conversion is obvious and possibly disastrous if fragile grazing land is converted to crops. Expanding the size and contents of the box they considered resulted in a large overestimation of the contribution of cattle.