The global livestock sector emits almost 6,000 million metric tonnes of carbon dioxide equivalent (MtCO2e) per year at 2008 levels and accounts for about 11 percent of global greenhouse gas emissions. Emissions from the sector are expected to increase 70 percent by 2050.
Methods, caveats and issues
Livestock emissions arise from the following sources (adapted from PBL, 2009: 170):
- Ruminants (sheep, cattle, goats) release methane during the digestion of food.
- Direct nitrous oxide (N2O) from livestock excreta (manure).
- Indirect emissions from the production of feed crops, as the production and use of fertilizer on land leads to emissions of CO2 and N2O.
- Deforestation and the conversion of grassland into arable land release significant amounts of CO2, methane (NH4) and nitrous oxide N2O from the soil.
- The transport of feed, livestock and animal products also causes emissions, but they are relatively small compared to the other sources.
Methods and assumptions
A key FAO report, Livestock's Long Shadow (FAO 2006), drew attention with its conclusion that (up to) 18 percent of global greenhouse gas emissions are associated with livestock. PBL sets the total at 6,000 MtCO2e per year, which adds up to 12 percent of the global GHG emissions. This is lower than the highest estimate in the FAO report (FAO 2006)—7.1 gigatonnes per year. One reason for this difference is that PBL (2009) use the most recent IPCC Guidelines (from 2006) for calculating nitrous oxide emissions, while the FAO use the previous version of the IPCC Guidelines. A second reason why the FAO gives a higher percentage (18 percent) is that FAO assumes a much lower total global emissions, i.e. 40 versus 48.9 GtCO2e (gigatonne carbon dioxide equivalent) per year (PBL, 2009: 170). However, as both PBL (2009) and FAO (2006) point out, the magnitude of the emissions caused by livestock is very difficult to quantify.
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- [PBL] Planbureau voor de Leefomgeving. 2009. Milieubalans 2009. Bilthoven: Planbureau voor de Leefomgeving. (Available from http://www.pbl.nl/nl/publicaties/2009/milieubalans/)
- Smith P, D Martino Z, Cai D, Gwary H, Janzen P et al. 2007. Agriculture. In: Metz B, Davidson OR, Bosch PR, Dave R, Meyer LA, eds. Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge: Cambridge University Press.
- Stehfest E, Bouwman AF, van Vuuren DP, den Elzen MGJ, Eickhout B et al. 2008. Vleesconsumptie en klimaatbeleid. Publicatienummer 500110004. Bilthoven: Planbureau voor de Leefomgeving.
- Garnett T. 2009. Livestock-related greenhouse gas emissions: impacts and options for policy makers. Environmental Science & Policy 12:491-503.
- [FAO] Food and Agriculture Organization of the United Nations. 2006. Livestock’s Long Shadow. Rome: FAO. (Available from http://www.fao.org/docrep/010/a0701e/a0701e00.HTM)