Editing IPCC:AR6/WGIII/Chapter-3 (section)

==== 3.3.2.4 Mitigation Strategies ====

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Detailed sectoral implications are discussed in [[#3.4|Section 3.4]] and Chapters 5–11 (see also Table 3.3). The stringency of climate policy has clear implications for mitigation action (Figure 3.15). There are a number of important commonalities of pathways limiting warming to 2°C (&gt;67%) or lower: for instance, they all rely on significant improvement of energy efficiency, rapid decarbonisation of supply and, many of them, CDR (in energy supply or AFOLU), either in terms of net negative emissions or to compensate residual emissions. Still, there are also important differences and the (IMPs) show how different choices can steer the system into alternative directions with different combinations of response options. For decarbonisation of energy supply many options exist, including CCS, nuclear power, and renewables (Chapter 6). In the majority of the scenarios reaching low GHG targets, a considerable amount of CCS is applied (Figure 3.15d). The share of renewables is around 30–70% in the scenarios that limit warming to 2°C (&gt;67%) and clearly above 40% for scenarios that limit warming 1.5°C (&gt;50%) (panel c). Scenarios have been published with 100% renewable energy systems even at a global scale, partly reflecting the rapid progress made for these technologies in the last decade ( [[#Creutzig--2017|Creutzig et al. 2017]] ; [[#Jacobson--2018|Jacobson et al. 2018]] ; [[#Breyer--2020|Breyer and Jefferson 2020]] ). These scenarios do not show in the graph due to a lack of information from non-energy sources. There is a debate in the literature on whether it is possible to achieve a 100% renewable energy system by 2050 ( [[#Brook--2018|Brook et al. 2018]] ). This critically depends on assumptions made on future system integration, system flexibility, storage options, consequences for material demand and the ability to supply high-temperature functions and specific mobility functions with renewable energy. The range of studies published showing 100% renewable energy systems show that it is possible to design such systems in the context of energy system models ( [[#Hong--2014a|Hong et al. 2014a]] ,b; [[#Lehtveer--2015a|Lehtveer and Hedenus 2015a]] ,b; [[#Pfenninger--2015|Pfenninger and Keirstead 2015]] ; [[#Sepulveda--2018|Sepulveda et al. 2018]] ; [[#Zappa--2019|Zappa et al. 2019]] ; [[#IEA--2021b|]] [[#IEA--2021|IEA 2021]] b ) (see also Box 6.6 on 100% renewables in net zero CO 2 systems). Panels e and f, finally, show the contribution of CDR – both in terms of net negative emissions and gross CDR. The contribution of total CDR obviously exceeds the net negative emissions. It should be noted that while a majority of scenarios rely on net negative emissions to reach stringent mitigation goals – this is not the case for all of them.

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[[File:b29202f6f1bb94302ce2f6aa8c80b128 IPCC_AR6_WGIII_Figure_3_15.png]]

'''Figure 3.15 | Characteristics of scenarios as a function of the remaining carbon budget (mean decarbonisation rate is shown as the average reduction in the period 2010–2050 divided by 2010 emissions).''' The categories C1–C7 are explained in Table 3.1.

The spread shown in Figure 3.15 implies different mitigation strategies that could all lead to emissions levels consistent with the Paris Agreement (and reach zero emissions). The IMPs illustrate some options for different decarbonisation pathways with heavy reliance on renewables ( ''IMP-Ren'' ), strong emphasis on energy-demand reductions ( ''IMP-LD'' ), widespread deployment of CDR methods coupled with CCS (BECCS and DACCS) ( ''IMP-Neg'' ), mitigation in the context of sustainable development ( ''IMP-SP'' ) (Figure 3.16). For example, in some scenarios, a small part of the energy system is still based on fossil fuels in 2100 ( ''IMP-Neg'' ), while in others, fossil fuels are almost or completely phased out ( ''IMP-Ren'' ). Nevertheless, in all scenarios, fossil fuel use is greatly reduced and unabated coal use is completely phased out by 2050. Also, nuclear power can be part of a mitigation strategy (however, the literature only includes some scenarios with high-nuclear contributions, such as [[#Berger--2017|Berger et al. 2017]] ). This is explored further in [[#3.5|Section 3.5]] . The different strategies are also clearly apparent in the way they scenarios reach net zero emissions. While ''IMP-GS'' and ''IMP-Neg'' rely significantly on BECCS and DACCS, their use is far more restricted in the other IMPs. Consistently, in these IMPs residual emissions are also significantly lower.

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[[File:f32648216ceab34d32ed0ce0e4820373 IPCC_AR6_WGIII_Figure_3_16.png]]

'''Figure 3.16 | Primary energy use and net emissions at net zero year for the different IMPS.''' Source: AR6 Scenarios Database.

Mitigation pathways also have a regional dimension. In 2010, about 40% of emissions originated from the Developed Countries and Eastern Europe and West Central Asia regions. According to the projections shown in Figure 3.17, the share of the latter regions will further increase to about 70% by 2050. In the scenarios in the literature, emissions are typically almost equally reduced across the regions.

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[[File:9cb143a622c7e8ef7e162f886b473979 IPCC_AR6_WGIII_Figure_3_17.png]]

'''Figure 3.17''' 11 '''| Emissions by region (including 5–95th percentile range).''' Source: AR6 Scenarios Database.

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