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

==== 5.5.1.4 Integrated approaches to crop and livestock mitigation ====

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'''Livestock mitigation in a circular economy.''' Novel technologies for increasing the integration of components in the food system are being devised to reduce GHG emissions. These include strategies that help decoupling livestock from land use. Work by van Zanten et al. (2018 <sup>[[#fn:r1451|1451]]</sup> )shows that 7–23 g of animal protein per capita per day could be produced without livestock competing for vital arable land. This would imply a contraction of the land area utilised by the livestock sector, but also a more efficient use of resources, and would lead to land sparing and overall emissions reductions.

Pikaar et al. (2018) <sup>[[#fn:r836|836]]</sup> demonstrated the technical feasibility of producing microbial protein as a feedstuff from sewage that could replace use of feed crops such as soybean. The technical potential of this novel practice could replace 10–19% of the feed protein required, and would reduce cropland demand and associated emissions by 6–7%. These practices are, however, not economically feasible nor easily upscalable in most systems. Nonetheless, significant progress in Japan and South Korea in the reduction and use of food waste to increase efficiencies in livestock food chains has been achieved, indicating a possible pathway to progress elsewhere (FAO 2017 <sup>[[#fn:r837|837]]</sup> ; zu Ermgassen et al. 2016 <sup>[[#fn:r838|838]]</sup> ). Better understanding of biomass and food and feed wastes, value chains, and identification of mechanisms for reducing the transport and processing costs of these materials is required to facilitate larger-scale implementation.

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'''Waste streams into energy''' . Waste streams from manure and food waste can be used for energy generation and thus reduction in overall GHG emissions in terms of recovered methane (for instance through anaerobic digestion) production (De Clercq et al. 2016 <sup>[[#fn:r839|839]]</sup> ) or for the production of microbial protein (Pikaar et al. 2018 <sup>[[#fn:r840|840]]</sup> ). Second-generation biorefineries, once the underlying technology is improved, may enable the generation of hydro-carbon from agricultural residues, grass, and woody biomass in ways that do not compete with food and can generate, along with biofuel, high-value products such as plastics (Nguyen et al. 2017 <sup>[[#fn:r841|841]]</sup> ). Second-generation energy biomass from residues may constitute a complementary income source for farmers that can increase their incentive to produce. Technologies include CHP (combined heat and power) or gas turbines, and fuel types such as biodiesel, biopyrolysis (i.e., high temperature chemical transformation of organic material in the absence of oxygen), torrefaction of biomass, production of cellulosic bioethanol and of bioalcohols produced by other means than fermentation, and the production of methane by anaerobic fermentation. (Nguyen et al. 2017 <sup>[[#fn:r842|842]]</sup> ).

'''Technology for reducing fossil fuel inputs''' . Besides biomass and bioenergy, other forms of renewable energy substitution for fossil fuels (e.g., wind, solar, geothermal, hydro) are already being applied on farms throughout the supply chain. Energy efficiency measures are being developed for refrigeration, conservation tillage, precision farming (e.g., fertiliser and chemical application and precision irrigation).

'''Novel technologies''' . Measures that can reduce livestock emissions given continued research and development include methane and nitrification inhibitors, methane vaccines, targeted breeding of lower-emitting animals, and genetically modified grasses with higher sugar content. New strategies to reduce methanogenesis include supplementing animal diets with antimethanogenic agents (e.g., 3-NOP, algae, chemical inhibitors such as chloroform) or supplementing with electron acceptors (e.g., nitrate) or dietary lipids. These could potentially contribute, once economically feasible at scale, to significant reductions of methane emissions from ruminant livestock. A well-tested compound is 3-nitrooxypropanol (3-NOP), which was shown to decrease methane by up to 40% when incorporated in diets for ruminants (Hristov et al. 2015 <sup>[[#fn:r843|843]]</sup> ).

Whilst these strategies may become very effective at reducing methane, they can be expensive and also impact on animal performance and/or welfare (Llonch et al. 2017 <sup>[[#fn:r844|844]]</sup> ). The use of novel fertilisers and/or plant species that secrete biological nitrification inhibitors also have the potential to significantly reduce N2O emissions from agricultural soils (Subbarao et al. 2009 <sup>[[#fn:r845|845]]</sup> ; Rose et al. 2018 <sup>[[#fn:r846|846]]</sup> ).

'''Economic mitigation potentials of crop and livestock sectors''' . Despite the large technical mitigation potential of the agriculture sector in terms of crop and livestock activities, its economic potential is relatively small in the short term (2030) and at modest carbon prices (less than 20 USD tC <sup>–1</sup> ). For crop and soil management practices, it is estimated that 1.0–1.5 GtCO <sub>2</sub> -eq yr <sup>–1</sup> could be a feasible mitigation target at a carbon price of 20 USD tC <sup>–1</sup> (Frank et al. 2018, 2017; Griscom et al. 2016 <sup>[[#fn:r847|847]]</sup> ; Smith et al. 2013 <sup>[[#fn:r848|848]]</sup> ; Wollenberg et al. 2016 <sup>[[#fn:r849|849]]</sup> ). For the livestock sector, these estimates range from 0.12–0.25 GtCO <sub>2</sub> -eq yr <sup>–1</sup> at similar carbon prices (Herrero et al. 2016c <sup>[[#fn:r850|850]]</sup> ; Henderson et al. 2017 <sup>[[#fn:r851|851]]</sup> ).

But care is needed in comparing crop and livestock economic mitigation potentials due to differing assumptions.

Frank et al. (2018) <sup>[[#fn:r852|852]]</sup> recently estimated that the economic mitigation potential of non-CO <sub>2</sub> emissions from agriculture and livestock to 2030 could be up to four times higher than indicated in the AR5, if structural options such as switching livestock species from ruminants to monogastrics, or allowing for flexibility to relocate production to more efficient regions were implemented, at the same time as the technical options such as those described above. At higher carbon prices (i.e., at about 100 USD tC–1), they found a mitigation potential of supply-side measures of 2.6 GtCO <sub>2</sub> -eq yr <sup>-1</sup> .

In this scenario, technical options would account for 38% of the abatement, while another 38% would be obtained through structural changes, and a further 24% would be obtained through shifts in consumption caused by food price increases. Key to the achievement of this mitigation potential lay in the livestock sector, as reductions in livestock consumption, structural changes and implementation of technologies in the sector had some of the highest impacts. Regions with the highest mitigation potentials were Latin America, China and Sub-Saharan Africa. The large-scale implementability of such proposed sweeping changes in livestock types and production systems is likely very limited as well as constrained by long-established socio-economic, traditional and cultural habits, requiring significant incentives to generate change.

In summary, supply-side practices can contribute to climate change mitigation by reducing crop and livestock emissions, sequestering carbon in soils and biomass, and by decreasing emissions intensity within sustainable production systems ( ''high confidence'' ). The AR5 estimated the total economic mitigation potential of crop and livestock activities as 1.5–4.0 GtCO <sub>2</sub> -eq yr <sup>–1</sup> by 2030 at prices ranging from 20–100 USD tCO <sub>2</sub> -eq ( ''high confidence'' ). Options with large potential for GHG mitigation in cropping systems include soil carbon sequestration (at decreasing rates over time), reductions in N <sub>2</sub> O emissions from fertilisers, reductions in CH <sub>4</sub> emissions from paddy rice, and bridging of yield gaps. Options with large potential for mitigation in livestock systems include better grazing land management, with increased net primary production and soil carbon stocks, improved manure management, and higher-quality feed. Reductions in GHG emissions intensity (emissions per unit product) from livestock can support reductions in absolute emissions, provided appropriate governance structures to limit total production are implemented at the same time ( ''medium confidence'' ).

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