Editing IPCC:AR6/WGIII/Chapter-7 (section)

==== 7.3.2.1 Livestock Populations and Management ====

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Enteric fermentation dominates agricultural CH 4 emissions ( [[#7.2.3|Section 7.2.3]] ) with emissions being a function of both ruminant animal numbers and productivity (output per animal). In addition to enteric fermentation, both CH 4 and N 2 O emissions from manure management (i.e., manure storage and application) and deposition on pasture, make livestock the main agricultural emissions source ( [[#Tubiello--2019|Tubiello 2019]] ). The AR5 reported increases in populations of all major livestock categories between the 1970s and 2000s, including ruminants, with increasing numbers directly linked with increasing CH 4 emissions (Smith et al. 2014). The SRCCL identified managed pastures as a disproportionately high N 2 O emissions source within grazing lands, with ''medium confidence'' that increased manure production and deposition was a key driver ( [[#Jia--2019|Jia et al. 2019]] ). The latest data ( [[#FAO--2021c|FAO 2021c]] ) indicate continued global livestock population growth between 1990 and 2019 (Figure 7.10), including increases of 18% in cattle and buffalo numbers, and 30% in sheep and goat numbers, corresponding with CH 4 emission trends. Data also indicate increased productivity per animal for example, average increases of 16% in beef, 17% in pig meat and 70% in whole (cow) milk per respective animal between 1990 and 2019 ( [[#FAO--2021c|FAO 2021c]] ). Despite these advances leading to reduced emissions per unit of product (calories, meat and milk) ( [[#FAO--2016|FAO 2016]] ; [[#Tubiello--2019|Tubiello 2019]] ), increased individual animal productivity generally requires increased inputs (e.g., feed) and this generates increased emissions ( [[#Beauchemin--2020|Beauchemin et al. 2020]] ). Manipulation of livestock diets, or improvements in animal genetics or health may counteract some of this. In addition, the production of inputs to facilitate increased animal productivity, may indirectly drive further absolute GHG emissions along the feed supply chain.

Although there are several potential drivers ( [[#McDermott--2010|McDermott et al. 2010]] ; [[#Alary--2015|Alary et al. 2015]] ), increased livestock production is principally in response to growth in demand for animal-sourced food, driven by a growing human population (FAO, 2019) and increased consumption resulting from changes in affluence, notably in middle-income countries ( [[#Godfray--2018|Godfray et al. 2018]] ). Available data document increases in total meat and milk consumption by 24 and 22% respectively between 1990 and 2013, as indicated by average annual per capita supply ( [[#FAO--2017a|FAO 2017a]] ). Updated data indicate that trends of increasing consumption continued between 2014 and 2018 ( [[#FAO--2021d|FAO 2021d]] ). Sustained demand for animal-sourced food is expected to drive further livestock sector growth, with global production projected to expand by 14% by 2029, facilitated by maintained product prices and lower feed prices ( [[#OECD/FAO--2019|OECD/FAO 2019]] ).

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