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

=== 7.2.3 CH 4 and N 2 O Flux From AFOLU ===

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Trends in atmospheric CH 4 and N 2 O concentrations and the associated sources, including land and land use are discussed in Sections 5.2.2 and 5.2.3 of the IPCC AR6 WGI. Regarding AFOLU, the SRCCL and AR5 ( [[#Jia--2019|Jia et al. 2019]] ; Smith et al. 2014) identified three global non-CO 2 emissions data sources: EDGAR ( [[#Crippa--2021|Crippa et al. 2021]] ), FAOSTAT ( [[#FAO--2021a|FAO 2021a]] ; [[#Tubiello--2019|Tubiello, 2019]] ) and the USA EPA ( [[#USEPA--2019|USEPA 2019]] ). Methodological differences have been previously discussed ( [[#Jia--2019|Jia et al. 2019]] ). In accordance with Chapter 2, this report, EDGAR data are used in Table 7.1 and Figure 7.3. It is important to note that in terms of AFOLU sectoral CH 4 and N 2 O emissions, only FAOSTAT provides data on AFOLU emissions, while EDGAR and USEPA data consider just the agricultural component. However, the mean of values across the three databases for both CH 4 and N 2 O, fall within the assessed uncertainty bounds (30 and 60% for CH 4 and N 2 O respectively, [[IPCC:Wg3:Chapter:Chapter-2#2.2.1|Section 2.2.1]] , in this report) of EDGAR data. NGHGIs annually submitted to the UNFCCC ( [[#7.2.2.3|Section 7.2.2.3]] ) provide national AFOLU CH 4 and N 2 O data, as included in the SRCCL ( [[#Jia--2019|Jia et al. 2019]] ). Aggregation of NGHGIs to indicate global emissions must be considered with caution, as not all countries compile inventories, nor submit annually. Additionally, NGHGIs may incorporate a range of methodologies for CH 4 and N 2 O accounting (e.g., [[#van%20der%20Weerden--2016|van der Weerden et al. 2016]] ; [[#Ndung’u--2019|Ndung’u et al. 2019]] ; [[#Thakuri--2020|Thakuri et al. 2020]] ), making comparison difficult. The analysis of complete AFOLU emissions presented here, is based on FAOSTAT data. For agricultural specific discussion, analysis considers EDGAR, FAOSTAT and USEPA data.

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==== 7.2.3.1 Global AFOLU CH 4 and N 2 O Emissions ====

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Using FAOSTAT data, the SRCCL estimated average CH 4 emissions from AFOLU to be 161.2 ± 43 MtCH 4 yr –1 for the period 2007–2016, representing 44% of total anthropogenic CH 4 emissions, with agriculture accounting for 88% of the AFOLU component ( [[#Jia--2019|Jia et al. 2019]] ). The latest data ( [[#FAO--2021a|FAO 2021a]] , 2020b) highlight a trend of growing AFOLU CH 4 emissions, with a 10% increase evident between 1990 and 2019, despite year-to-year variation. Forestry and other land use (FOLU) CH 4 emission sources include biomass burning on forest land and combustion of organic soils (peatland fires) ( [[#FAO--2020c|FAO 2020c]] ). The agricultural share of AFOLU CH 4 emissions remains relatively unchanged, with the latest data indicating agriculture to have accounted for 89% of emissions on average between 1990 and 2019. The SRCCL reported with ''medium evidence'' and ''high agreement'' that ruminants and rice production were the most important contributors to overall growth trends in atmospheric CH 4 ( [[#Jia--2019|Jia et al. 2019]] ). The latest data confirm this in terms of agricultural emissions, with agreement between databases that agricultural CH 4 emissions continue to increase and that enteric fermentation and rice cultivation remain the main sources (Figure 7.7). The proportionally higher emissions from rice cultivation indicated by EDGAR data compared to the other databases, may result from the use of a Tier 2 methodology for this source within EDGAR ( [[#Janssens-Maenhout--2019|Janssens-Maenhout et al. 2019]] ).

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'''Figure 7.7 | Estimated global mean agricultural CH''' 4 '''(top), N''' 2 '''O (middle) and aggregated CH''' 4 '''and N''' 2 '''O (using CO''' 2 '''-eq according to GWP100 AR6 values).''' '''(Bottom) emissions for three decades according to EDGAR v6.0 (Crippa''' '''et al.''' '''2021), FAOSTAT ( [[#FAO--2021a|FAO 2021a]] ) and USEPA ( [[#USEPA--2019|USEPA 2019]] ) databases.''' Latest versions of databases indicate historic emissions to 2019, 2019 and 2015 respectively, with average values for the post–2010 period calculated accordingly. For CH 4 , emissions classified as ‘Other Ag.’ within USEPA data, are re-classified as ‘Agricultural Biomass Burning’. Despite CH 4 emissions from agricultural soils also being included, this category was deemed to principally concern biomass burning on agricultural land and classified accordingly. For N 2 O, emissions classified within EDGAR as direct and indirect emissions from managed soils, and indirect emissions from manure management are combined under ‘Agricultural Soils’. Emissions classified by FOASTAT as from manure deposition and application to soils, crop residues, drainage of organic soils and synthetic fertilisers are combined under ‘Agricultural Soils’, while emissions reported as ‘Other Ag.’ under USEPA data are re-classified as ‘Agricultural Biomass Burning’.

The SRCCL also noted a trend of increasing atmospheric N 2 O concentration, with ''robust evidence'' and ''high agreement'' that agriculture accounted for approximately two-thirds of overall global anthropogenic N 2 O emissions. Average AFOLU N 2 O emissions were reported to be 8.7 ± 2.5 MtN 2 O yr –1 for the period 2007–2016, accounting for 81% of total anthropogenic N 2 O emissions, with agriculture accounting for 95% of AFOLU N 2 O emissions ( [[#Jia--2019|Jia et al. 2019]] ). A recent comprehensive review confirms agriculture as the principal driver of the growing atmospheric N 2 O concentration ( [[#Tian--2020|Tian et al. 2020]] ). The latest FAOSTAT data ( [[#FAO--2020b|FAO 2020b]] , 2021a) document a 25% increase in AFOLU N 2 O emissions between 1990 and 2019, with the average share from agriculture remaining approximately the same (96%). Agricultural soils were identified in the SRCCL and in recent literature as a dominant emission source, notably due to nitrogen fertiliser and manure applications to croplands, and manure production and deposition on pastures ( [[#Jia--2019|Jia et al. 2019]] ; [[#Tian--2020|Tian et al. 2020]] ). There is agreement within latest data that agricultural soils remain the dominant source (Figure 7.7).

Aggregation of CH 4 and N 2 O to CO 2 equivalence (using GWP100 IPCC AR6 values), suggests that AFOLU emissions increased by 15% between 1990 and 2019, though emissions showed trend variability year to year. Agriculture accounted for 91% of AFOLU emissions on average over the period ( [[#FAO--2020b|FAO 2020b]] , 2021a). EDGAR ( [[#Crippa--2021|Crippa et al. 2021]] ), FAOSTAT ( [[#FAO--2021a|FAO 2021a]] ) and USEPA ( [[#USEPA--2019|USEPA 2019]] ) data suggest aggregated agricultural emissions (CO 2 -eq) to have increased since 1990, by 19% (1990–2019), 15% (1990–2019) and 21% (1990–2015) respectively, with all databases identifying enteric fermentation and agricultural soils as the dominant agricultural emissions sources.

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==== 7.2.3.2 Regional AFOLU CH 4 and N 2 O Emissions ====

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FAOSTAT data ( [[#FAO--2020b|FAO 2020b]] , 2021a) indicate Africa (+44%), followed by Southern Asia (+29%) to have the largest growth in AFOLU CH 4 emissions between 1990 and 2019 (Figure 7.8). Eurasia was characterised by notable emission reductions (–58%), principally as a result of a sharp decline (–63%) between 1990 and 1999. The average agricultural share of AFOLU emissions between 1990 and 2019 ranged from 66% in Africa to almost 100% in the Middle East.

In agreement with AR5 (Smith et al. 2014), the SRCCL identified Asia as having the largest share (37%) of emissions from enteric fermentation and manure management since 2000, but Africa to have the fastest growth rate. Asia was identified as responsible for 89% of rice cultivation emissions, which were reported as increasing ( [[#Jia--2019|Jia et al. 2019]] ). Considering classification by ten IPCC regions, data suggest enteric fermentation to have dominated emissions in all regions since 1990, except in South-East Asia and Pacific, where rice cultivation forms the principal source (FAO 2021; [[#USEPA--2019|USEPA 2019]] ). The different databases broadly indicate the same regional CH 4 emission trends, though the indicated absolute change differs due to methodological differences ( [[#7.2.3.1|Section 7.2.3.1]] ). All databases indicate considerable emissions growth in Africa since 1990 and that this region recorded the greatest regional increases in emissions from both enteric fermentation and rice cultivation since 2010. Additionally, FAOSTAT data suggest that emissions from agricultural biomass burning account for a notably high proportion of agricultural CH 4 emissions in Africa (Figure 7.8).

The latest data suggest growth in AFOLU N 2 O emissions in most regions between 1990 and 2019, with Southern Asia demonstrating highest growth (+74%) and Eurasia, greatest reductions (–51%), the latter mainly a result of a 61% reduction between 1990 and 2000 ( [[#FAO--2020b|FAO 2020b]] , 2021a). Agriculture was the dominant emission source in all regions, its proportional average share between 1990 and 2019 ranging from 87% in Africa, to almost 100% in the Middle East (Figure 7.8).

The SRCCL provided limited discussion on regional variation in agricultural N 2 O emissions but reported with ''medium confidence'' that certain regions (North America, Europe, East and South Asia) were notable sources of grazing land N 2 O emissions ( [[#Jia--2019|Jia et al. 2019]] ). The AR5 identified Asia as the largest source and as having the highest growth rate of N 2 O emissions from synthetic fertilisers between 2000 and 2010 (Smith et al. 2014). Latest data indicate agricultural N 2 O emission increases in most regions, though variation between databases prevents definitive conclusions on trends, with Africa, Southern Asia, and Eastern Asia suggested to have had greatest growth since 1990 according to EDGAR ( [[#Crippa--2021|Crippa et al. 2021]] ), FAOSTAT ( [[#FAO--2021a|FAO 2021a]] ) and USEPA ( [[#USEPA--2019|USEPA 2019]] ) data respectively. However, all databases indicate that emissions declined in Eurasia and Europe from 1990 levels, in accordance with specific environmental regulations put in place since the late 1980s ( [[#Tubiello--2019|Tubiello 2019]] ; [[#European%20Environment%20Agency--2020|European Environment Agency 2020]] ; [[#Tian--2020|Tian et al. 2020]] ), but generally suggest increases in both regions since 2010.

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'''Figure 7.8 | Estimated average AFOLU CH''' 4 '''(top) and N''' 2 '''O (bottom) emissions for three decades according to FAOSTAT data by ten global regions, with disaggregation of agricultural emissions ( [[#FAO--2020b|FAO 2020b]] ; 2021a).''' Note for N 2 O: emissions from manure deposition and application to soils, crop residues and synthetic fertilisers are combined under ‘Agriculture: Soils’.

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