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

=== 7.5.5 Illustrative Mitigation Pathways ===

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Different mitigation strategies can achieve the net emission reductions that would be required to follow a pathway limiting global warming, with very different consequences for the land system. Figure 7.17 shows Illustrative Mitigation Pathways (IMPs) for achieving different climate targets highlighting AFOLU mitigation strategies, resulting GHG and land-use dynamics as well as the interaction with other sectors. For consistency this chapter discusses IMPs as described in detail in chapters 1 and 3 of this report but focusing on the land-use sector. All pathways are assessed by different IAM realisations and do not only reduce GHG emissions but also use CDR options, whereas the amount and timing varies across pathways, as do the relative contributions of different land-based CDR options.

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'''Figure 7.17 | Evolution and breakdown of (a) global land-based GHG emissions and removals and (b) global land-use dynamics under four Illustrative Mitigation Pathways, which illustrate the differences in timing and magnitude of land-based mitigation approaches including afforestation and BECCS.''' All pathways are based on different IAM realisations: ModAct scenario (below 3.0°C, C6) from IMAGE 3.0; IMP Neg-2.0 (limit warming to 2°C (&gt;67%), C3) from AIM/CGE 2.2; IMP Ren (1.5°C with no or low overshoot, C1) from REMIND-MAgPIE 2.1–4.3; IMP SP (1.5°C with no or low overshoot, C1) from REMIND-MAgPIE 2.1–4.2. In panel A the categories CO 2 AFOLU, CH 4 AFOLU and N 2 O AFOLU include GHG emissions from land-use change and agricultural land use (including emissions related to bioenergy production). In addition, the category CO 2 Land includes removals due to afforestation/reforestation. BECCS reflects the CO 2 emissions captured from bioenergy use and stored in geological deposits. CH 4 and N 2 O emissions are converted to CO 2 -eq using GWP100 factors of 27 and 273 respectively.

The scenario ''ModAct'' (limit warming to 3°C (&gt;50%), C6) is based on the prolongation of current trends (SSP2) but contains measures to strengthen policies for the implementation of National Determined Contributions (NDCs) in all sectors including AFOLU ( [[#Grassi--2018|Grassi et al. 2018]] ). This pathway shows a strong decrease of CO 2 emissions from land-use change in 2030, mainly due to reduced deforestation, as well as moderately decreasing N 2 O and CH 4 emissions from agricultural production due to improved agricultural management and dietary shifts away from emissions-intensive livestock products. However, in contrast to CO 2 emissions, which turn net-negative around 2050 due to afforestation/reforestation, CH 4 and N 2 O emissions persist throughout the century due to difficulties of eliminating these residual emissions based on existing agricultural management methods ( [[#Frank--2017|Frank et al. 2017]] ; [[#Stevanović--2017|Stevanović et al. 2017]] ). Comparably small amounts of BECCS are applied by the end of the century. Forest area increases at the cost of other natural vegetation.

''IMP-Neg'' is similar to ''ModAct'' scenario in terms of socio-economic setting (SSP2) but differs strongly in terms of the mitigation target (limit warming to 2°C (&gt;67%), C3) and its strong focus on the supply side of mitigation measures with strong reliance on net-negative emissions. Consequently, all GHG emission reductions as well as afforestation/reforestation and BECCS-based CDR start earlier in time at a higher rate of deployment. However, in contrast to CO 2 emissions, which turn net-negative around 2030 due to afforestation/reforestation, CH 4 and N 2 O emissions persist throughout the century, similar to ''ModAct'' , due to ongoing increasing demand for total calories and animal-based commodities ( [[#Bodirsky--2020|Bodirsky et al. 2020]] ) and difficulties of eliminating these residual emissions based on existing agricultural management methods ( [[#Stevanović--2017|Stevanović et al. 2017]] ; [[#Frank--2017|Frank et al. 2017]] ). In addition to abating land-related GHG emissions as well as increasing the terrestrial sink, this example also shows the potential importance of the land sector in providing biomass for BECCS and hence CDR in the energy sector. Cumulative CDR (2020–2100) amounts to 502 GtCO 2 for BECCS and 121 GtCO 2 for land-use change (including afforestation and reduced deforestation). In consequence, compared to ''ModAct'' scenario '','' competition for land is increasing and much more other natural land as well as agricultural land (cropland and pasture land) is converted to forest or bioenergy cropland with potentially severe consequences for various sustainability dimensions such as biodiversity ( [[#Hof--2018|Hof et al. 2018]] ) and food security ( [[#Fujimori--2019|Fujimori et al. 2019]] ).

''IMP-Ren'' is similar to ''IMP Neg-2.0'' in terms of socio-economic setting (SSP2) but differs substantially in terms of mitigation target and mitigation efforts in the energy sector. Even under the more ambitious climate change mitigation target (1.5°C with no or low overshoot (OS), C1), the high share of renewable energy in ''IMP Ren'' strongly reduces the need for large-scale land-based CDR, which is reflected in smaller bioenergy and afforestation areas compared to ''IMP Neg-2.0'' . However, CH 4 and N 2 O emissions from AFOLU persist throughout the century, similar to ''ModAct'' scenario and ''IMP Neg-2.0'' .

In contrast to ''IMPs Neg-2.0'' and ''Ren, IMP SP'' ( [[#Soergel--2021|Soergel et al. 2021]] ; 1.5°C with no or low OS, C1) displays a future of generally low resource and energy consumption (including healthy diets with low animal-calorie shares and low food waste) as well as significant but sustainable agricultural intensification in combination with high levels of nature protection. This pathway shows a strong near-term decrease of CO 2 emissions from land-use change, mainly due to reduced deforestation, and in difference to all other IMPs described in this chapter strongly decreasing N 2 O and CH 4 emissions from agricultural production due to improved agricultural management but also based on dietary shifts away from emissions-intensive livestock products as well as lower shares of food waste. In consequence, comparably small amounts of land are needed for land demanding mitigation activities such as BECCS and afforestation. In particular, the amount of agricultural land converted to bioenergy cropland is smaller compared to other mitigation pathways. Forest area increases either by regrowth of secondary vegetation following the abandonment of agricultural land or by afforestation/reforestation at the cost of agricultural land.

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