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

=== 7.3.2 Anthropogenic Direct Drivers – Agriculture ===

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==== 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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==== 7.3.2.2 Rice Cultivation ====

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In addition to livestock, both AR5 and the SRCCL identified paddy rice cultivation as an important emissions source (Smith et al. 2014), with ''medium evidence'' and ''high agreement'' that its expansion is a key driver of growing trends in atmospheric CH 4 concentration ( [[#Jia--2019|Jia et al. 2019]] ). The latest data indicate the global harvested area of rice to have grown by 11% between 1990 and 2019, with total paddy production increasing by 46%, from 519 Mt to 755 Mt ( [[#FAO--2021c|FAO 2021c]] ). Global rice production is projected to increase by 13% by 2028 compared to 2019 levels ( [[#OECD/FAO--2019|OECD/FAO 2019]] ). However, yield increases are expected to limit cultivated area expansion, while dietary shifts from rice to protein as a result of increasing per capita income, is expected to reduce demand in certain regions, with a slight decline in related emissions projected to 2030 ( [[#USEPA--2019|USEPA 2019]] ).

Between 1990 and 2019, Africa recorded the greatest increase (+160%) in area under rice cultivation, followed by Asia and the Pacific (+6%), with area reductions evident in all other regions ( [[#FAO--2021c|FAO 2021c]] ) broadly corresponding with related regional CH 4 emission (Figures 7.3 and 7.8). Data indicate the greatest growth in consumption (average annual supply per capita) between 1990 and 2013 to have occurred in Eastern Europe and West Central Asia (+42%) followed by Africa (+25%), with little change (+1%) observed in Asia and the Pacific ( [[#FAO--2017a|FAO 2017a]] ). Most of the projected increase in global rice consumption is in Africa and Asia ( [[#OECD/FAO--2019|OECD/FAO 2019]] ).

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==== 7.3.2.3 Synthetic Fertiliser Use ====

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Both AR5 and the SRCCL described considerable increases in global use of synthetic nitrogen fertilisers since the 1970s, which was identified to be a major driver of increasing N 2 O emissions ( [[#Jia--2019|Jia et al. 2019]] ). The latest data document a 41% increase in global nitrogen fertiliser use between 1990 and 2019 ( [[#FAO--2021e|FAO 2021e]] ) corresponding with associated increased N 2 O emissions (Figure 7.3). Increased fertiliser use has been driven by pursuit of increased crop yields, with for example, a 61% increase in average global cereal yield per hectare observed during the same period ( [[#FAO--2021c|FAO 2021c]] ), achieved through both increased fertiliser use and varietal improvements. Increased yields are in response to increased demand for food, feed, fuel and fibre crops which in turn has been driven by a growing human population (FAO, 2019), increased demand for animal-sourced food and bioenergy policy ( [[#OECD/FAO--2019|OECD/FAO 2019]] ). Global crop production is projected to increase by almost 15% over the next decade, with low income and emerging regions with greater availability of land and labour resources expected to experience the strongest growth, and account for about 50% of global output growth ( [[#OECD/FAO--2019|OECD/FAO 2019]] ). Increases in global nitrogen fertiliser use are also projected, notably in low income and emerging regions ( [[#USEPA--2019|USEPA 2019]] ).

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