Editing IPCC:AR6/SRCCL/Chapter-2 (section)

==== 2.3.2.2 Land use effects ====

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Agricultural emissions are predominantly from enteric fermentation and rice, with manure management and waste burning contributing<br />
small amounts (Figure 2.9). Since 2000, livestock production has been responsible for 33% of total global emissions and 66% of agricultural emissions (EDGAR 4.3.2 database, May 2018; USEPA 2012 <sup>[[#fn:r628|628]]</sup> ; Tubiello et al. 2014 <sup>[[#fn:r629|629]]</sup> ; Janssens-Maenhout et al. 2017b <sup>[[#fn:r630|630]]</sup> ). Asia has the largest livestock emissions (37%) and emissions in the region have been growing by around 2% per year over the same period.

North America is responsible for 26% and emissions are stable; Europe is responsible for around 8% of emissions, and these are decreasing slightly (&lt;1% per year). Africa is responsible for 14%, but emissions are growing fastest in this region at around 2.5% y <sup>–1</sup> . In Latin America and the Caribbean, livestock emissions are decreasing at around 1.6% per year and the region makes up 16% of emissions.

Rice emissions are responsible for about 24% of agricultural emissions and 89% of these are from Asia. Rice emissions are increasing by 0.9% per year in that region. These trends are predicted to continue through 2030 (USEPA 2013 <sup>[[#fn:r631|631]]</sup> ).

Upland soils are a net sink of atmospheric CH <sub>4</sub> , but soils both produce and consume the gas. On the global scale, climatic zone, soil texture and land cover have an important effect on CH <sub>4</sub> uptake in upland soils (Tate 2015 <sup>[[#fn:r632|632]]</sup> ; Yu et al. 2017 <sup>[[#fn:r633|633]]</sup> ; Dutaur and Verchot 2007 <sup>[[#fn:r634|634]]</sup> ). Boreal soils take up less than temperate or tropical soils, coarse textured soils take up more CH <sub>4</sub> than medium and fine textured soils, and forests take up more than other ecosystems. Low levels of nitrogen fertilisation or atmospheric deposition can affect the soil microbial community and stimulate soil CH <sub>4</sub> uptake in nitrogen-limited soils, while higher fertilisation rates decrease uptake (Edwards et al. 2005 <sup>[[#fn:r635|635]]</sup> ; Zhuang et al., 2013 <sup>[[#fn:r636|636]]</sup> ). Globally, nitrogen fertilisation on agricultural lands may have suppressed CH <sub>4</sub> oxidation by as much as 26 Tg between 1998 and 2004 ( ''low confidence, low agreement'' ) (Zhuang et al., 2013 <sup>[[#fn:r637|637]]</sup> ). The effect of nitrogen additions is cumulative and repeated fertilisation events have progressively greater suppression effects ( ''robust evidence, high agreement'' ) (Tate 2015 <sup>[[#fn:r638|638]]</sup> ). Other factors such as higher temperatures, increased atmospheric concentrations and changes in rainfall patterns stimulate soil CH <sub>4</sub> consumption in unfertilised ecosystems. Several studies (Yu et al. 2017 <sup>[[#fn:r639|639]]</sup> ; Xu et al. 2016 <sup>[[#fn:r640|640]]</sup> ; Curry 2009 <sup>[[#fn:r641|641]]</sup> ) have shown that globally, uptake has been increasing during the second half of the 20th century and is expected to continue to increase by as much as 1 Tg in the 21st century, particularly in forests and grasslands ( ''medium evidence, high agreement'' ).

Northern peatlands (40–70°N) are a significant source of atmospheric CH <sub>4</sub> , emitting about 48 TgCH <sub>4</sub> , or about 10% of the total emissions to the atmosphere (Zhuang et al. 2006 <sup>[[#fn:r642|642]]</sup> ; Wuebbles and Hayhoe 2002 <sup>[[#fn:r643|643]]</sup> ). CH <sub>4</sub> emissions from natural northern peatlands are highly variable, with the highest rate from fens ( ''medium evidence, high agreement'' ). Peatland management and restoration alters the exchange of CH <sub>4</sub> with the atmosphere ( ''medium evidence, high agreement'' ). Management of peat soils typically converts them from CH <sub>4</sub> sources to sinks (Augustin et al. 2011 <sup>[[#fn:r644|644]]</sup> ; Strack and Waddington 2008 <sup>[[#fn:r645|645]]</sup> ; Abdalla et al. 2016 <sup>[[#fn:r646|646]]</sup> ) ( ''robust evidence, high agreement'' ). While restoration decreases CO <sub>2</sub> emissions (Section 4.9.4), CH <sub>4</sub> emissions often increase relative to the drained conditions ( ''robust evidence, high agreement'' ) (Osterloh et al. 2018 <sup>[[#fn:r647|647]]</sup> ; Christen et al. 2016 <sup>[[#fn:r648|648]]</sup> ; Koskinen et al. 2016 <sup>[[#fn:r649|649]]</sup> ; Tuittila et al. 2000 <sup>[[#fn:r650|650]]</sup> ; Vanselow-Algan et al. 2015 <sup>[[#fn:r651|651]]</sup> ; Abdalla et al. 2016 <sup>[[#fn:r652|652]]</sup> ). Drained peatlands are usually considered to be negligible methane sources, but they emit CH <sub>4</sub> under wet weather conditions and from drainage ditches (Drösler et al. 2013 <sup>[[#fn:r653|653]]</sup> ; Sirin et al. 2012 <sup>[[#fn:r654|654]]</sup> ). While ditches cover only a small percentage of the drained area, emissions can be sufficiently high that drained peatlands emit comparable CH <sub>4</sub> as undrained ones ( ''medium evidence, medium agreement'' ) (Sirin et al. 2012 <sup>[[#fn:r655|655]]</sup> ; Wilson et al. 2016 <sup>[[#fn:r656|656]]</sup> ).

Because of the large uncertainty in the tropical peatland area, estimates of the global flux are highly uncertain. A meta-analysis of the effect of conversion of primary forest to rice production showed that emissions increased by a factor of four ( ''limited evidence, high agreement'' ) (Hergoualc’h and Verchot, 2012 <sup>[[#fn:r657|657]]</sup> ). For land uses that required drainage, emissions decreased by a factor of three ( ''limited evidence, high agreement'' ).There are no representative measurements of emissions from drainage ditches in tropical peatlands.

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'''Figure 2.9'''

<span id="average-agricultural-ch4-emissions-estimates-from-1990.-sub-sectorial-agricultural-emissions-are-based-on-the-emissions-database-for-global-atmospheric-research-edgar-v4.3.2-janssens-maenhout-et-al.-2017a-faostat-tubiello-et-al.-2013-and-national-ghgi-data-grassi-et-al.-2018.-ghgi-data-are-aggregate-values-for-the-sector.-note-that-edgar-data-are-complete-only-through"></span>
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'''Average agricultural CH4 emissions estimates from 1990. Sub-sectorial agricultural emissions are based on the Emissions Database for Global Atmospheric Research (EDGAR v4.3.2; Janssens-Maenhout et al. 2017a); FAOSTAT (Tubiello et al. 2013); and National GHGI data (Grassi et al. 2018). GHGI data are aggregate values for the sector. Note that EDGAR data are complete only through […]'''
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[[File:36b982b2b8d180f89286cbcde6c789c0 Figure-2.9-1024x599.jpg]]

Average agricultural CH <sub>4</sub> emissions estimates from 1990. Sub-sectorial agricultural emissions are based on the Emissions Database for Global Atmospheric Research (EDGAR v4.3.2; Janssens-Maenhout et al. 2017a <sup>[[#fn:r658|658]]</sup> ); FAOSTAT (Tubiello et al. 2013 <sup>[[#fn:r659|659]]</sup> ); and National GHGI data (Grassi et al. 2018 <sup>[[#fn:r660|660]]</sup> ). GHGI data are aggregate values for the sector. Note that EDGAR data are complete only through 2012; the data in the right-hand panel represent the three years 2010–2012 and are presented for comparison.

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