Editing IPCC:AR6/SRCCL/Chapter-5 (section)

=== 5.4.3 Greenhouse gas emissions from livestock ===

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Emissions from livestock include non-CO <sub>2</sub> gases from enteric fermentation from ruminant animals and from anaerobic fermentation in manure management processes, as well as non-CO <sub>2</sub> gases from manure deposited on pastures (Smith et al. 2014 <sup>[[#fn:r693|693]]</sup> ). Estimates after the AR5 include those from Herrero et al. (2016) <sup>[[#fn:r694|694]]</sup> , who quantified non-CO <sub>2</sub> emissions from livestock to be in the range of 2.0–3.6 GtCO <sub>2</sub> -eq yr <sup>-1</sup> , with enteric fermentation from ruminants being the main contributor. FAOSTAT (2018) <sup>[[#fn:r695|695]]</sup> estimates of these emissions, renormalized to AR5 GWP values, were 4.1 ± 1.2 GtCO <sub>2</sub> -eq yr <sup>–1</sup> over the period 2010–2016.

These estimates of livestock emissions are for those generated within the farm gate.Adding emissions from relevant land-use change, energy use, and transportation processes, FAO (2014a) and Gerber et al. (2013) estimated livestock emissions of up to 5.3 ±1.6 GtCO <sub>2</sub> -eq yr <sup>–1</sup> circa the year 2010. This data came from original papers, but was scaled to SAR global warming potential (GWP) values for methane, for comparability with previous results.

All estimates agree that cattle are the main source of global livestock emissions (65–77%). Livestock in low and middle-income countries contribute 70% of the emissions from ruminants and 53% from monogastric livestock (animals without ruminant digestion processes such as pigs and poultry), and these are expected to increase as demand for livestock products increases in these countries (Figure 5.10). In contrast to the increasing trend in absolute GHG emissions, GHG emissions intensities, defined as GHG emissions per unit produced, have declined globally and are about 60% lower today than in the 1960s. This is largely due to improved meat and milk productivity of cattle breeds (FAOSTAT 2018 <sup>[[#fn:r696|696]]</sup> ; Davis et al. 2015 <sup>[[#fn:r697|697]]</sup> ).

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'''Figure 5.10'''

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'''Global GHG emissions from livestock for 1995–2005 (adapted from Herrero et al. 2016a).'''
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[[File:91828479746a640ab3c39bab4e05a70c Figure-5.10-1024x469.jpg]]

Global GHG emissions from livestock for 1995–2005 (adapted from Herrero et al. 2016a <sup>[[#fn:r1440|1440]]</sup> ).

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Still, products like red meat remain the most inefficient in terms of emissions per kg of protein produced in comparison to milk, pork, eggs and all crop products (IPCC 2014b <sup>[[#fn:r698|698]]</sup> ). Yet, the functional unit used in these measurements is highly relevant and may produce different results (Salou et al. 2017 <sup>[[#fn:r699|699]]</sup> ). For instance, metrics based on products tend to rate intensive livestock systems as efficient, while metrics based on area or resources used tend to rate extensive systems as efficient (Garnett 2011 <sup>[[#fn:r700|700]]</sup> ). In ruminant dairy systems, less intensified farms show higher emissions if expressed by product, and lower emissions if expressed by Utilizable Agricultural Land (Gutiérrez-Peña et al. 2019 <sup>[[#fn:r701|701]]</sup> ; Salvador et al. 2017 <sup>[[#fn:r702|702]]</sup> ; Salou et al. 2017 <sup>[[#fn:r703|703]]</sup> ).

Furthermore, if other variables are used in the analysis of GHG emissions of different ruminant production systems, such as human-edible grains used to feed animals instead of crop waste and pastures of marginal lands, or carbon sequestration in pasture systems in degraded lands, then the GHG emissions of extensive systems are reduced. Reductions of 26% and 43% have been shown in small ruminants, such as sheep and goats (Gutiérrez-Peña et al. 2019 <sup>[[#fn:r704|704]]</sup> ; Salvador et al. 2017 <sup>[[#fn:r705|705]]</sup> ; Batalla et al. 2015 <sup>[[#fn:r706|706]]</sup> and Petersen et al. 2013 <sup>[[#fn:r707|707]]</sup> ). In this regard, depending on what the main challenge is in different regions (for example, undernourishment, over-consumption, natural resources degradation), different metrics could be used as reference. Other metrics that consider nutrient density have been proposed because they provide potential for addressing both mitigation and health targets (Doran-Browne et al. 2015 <sup>[[#fn:r708|708]]</sup> ).

Uncertainty in worldwide livestock population numbers remains the main source of variation in total emissions of the livestock sector, while at the animal level, feed intake, diet regime, and nutritional composition are the main sources of variation through their impacts on enteric fermentation and manure N excretion.

Increases in economies of scale linked to increased efficiencies and decreased emission intensities may lead to more emissions, rather than less, an observed dynamic referred to by economists as a ‘rebound effect’. This is because increased efficiency allows production processes to be performed using fewer resources and often at lower cost. This in turn influences consumer behaviour and product use, increasing demand and leading to increased production. In this way, the expected gains from new technologies that increase the efficiency of resource use may be reduced (for example, increase in the total production of livestock despite increased efficiency of production due to increased demand for meat sold at lower prices). Thus, in order for the livestock sector to provide a contribution to GHG mitigation, reduction in emissions intensities need to be accompanied by appropriate governance and incentive mechanisms to avoid rebound effects, such as limits on total production.

Variation in estimates of N <sub>2</sub> O emissions are due to differing (i) climate regimes, (ii) soil types, and (iii) N transformation pathways (Charles et al. 2017 and Fitton et al. 2017). It was recently suggested that N <sub>2</sub> O soil emissions linked to livestock through manure applications could be 20–40% lower than previously estimated in some regions. For instance, in Sub-Saharan Africa and Eastern Europe (Gerber et al. 2016 <sup>[[#fn:r709|709]]</sup> ) and from smallholder systems in East Africa (Pelster et al. 2017 <sup>[[#fn:r710|710]]</sup> ). Herrero et al. (2016a) estimated global livestock enteric methane to range from 1.6–2.7 Gt CO <sub>2</sub> -eq, depending on assumptions of body weight and animal diet.

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