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

=== 3.5.3 Global Accelerated Action Towards Long-term Climate Goals ===

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A growing literature explores long-term mitigation pathways with accelerated near-term action going beyond the NDCs ( [[#Graichen--2017|Graichen et al. 2017]] ; [[#Jiang--2017|Jiang et al. 2017]] ; [[#Kriegler--2018a|Kriegler et al. 2018a]] ; [[#Roelfsema--2018|Roelfsema et al. 2018]] ; [[#Fekete--2021|Fekete et al. 2021]] ; [[#van%20Soest--2021a|van Soest et al. 2021a]] ). Global accelerated action pathways are designed to transition more gradually from implemented policies and planned implementation of NDCs onto a 1.5°C–2°C pathway and at the same time alleviate the abrupt transition in 2030 that would be caused by following the NDCs until 2030 and strengthening towards limiting warming to 2°C thereafter ( [[#3.5.2|Section 3.5.2]] ). Therefore, they have sometimes been called bridging scenarios/pathways in the literature ( [[#IEA--2011|IEA 2011]] ; [[#Spencer--2015|Spencer et al. 2015]] ; [[#van%20Soest--2021a|van Soest et al. 2021a]] ). They rely on regionally differentiated regulatory and pricing policies to gradually strengthening regional and sectoral action beyond the mitigation ambition in the NDCs. There are limitations to this approach. The tighter the warming limit, the more likely it is that disruptive action becomes inevitable to achieve the speed of transition that would be required ( [[#Kriegler--2018a|Kriegler et al. 2018a]] ). Cost-effective pathways already have abrupt shifts in deployments, investments and prices at the time a stringent warming limit is imposed, reflecting the fact that the overall response to climate change has so far been misaligned with long-term climate goals ( [[#Fawcett--2015|Fawcett et al. 2015]] ; [[#Rogelj--2016|Rogelj et al. 2016]] ; [[#Schleussner--2016b|Schleussner et al. 2016b]] ; [[#Geiges--2020|Geiges et al. 2020]] ). Disruptive action can help to break lock-ins and enable transformative change ( [[#Vogt-Schilb--2018|Vogt-Schilb et al. 2018]] ).

The large literature on accelerating climate action was assessed in the ''IPCC Special Report on Global Warming of 1.5°C'' ( [[#de%20Coninck--2018|de Coninck et al. 2018]] ) and is taken up in this report primarily in Chapters 4, 13, and 14. Accelerating climate action and facilitating transformational change requires a perspective on socio-technical transitions ( [[#Geels--2016a|Geels et al. 2016a]] ; [[#Geels--2016b|Geels et al. 2016b]] ; Geels 2020), a portfolio of policy instruments to manage technological and environmental change ( [[#Fischer--2008|Fischer and Newell 2008]] ; [[#Goulder--2008|Goulder and Parry 2008]] ; Acemoglu et al. 2012, 2016), a notion of path dependency and policy sequencing ( [[#Pierson--2000|Pierson 2000]] ; [[#Meckling--2017|Meckling et al. 2017]] ; [[#Pahle--2018|Pahle et al. 2018]] ) and the evolvement of polycentric governance layers of institutions and norms in support of the transformation ( [[#Dietz--2003|Dietz et al. 2003]] ; [[#Leach--2007|Leach et al. 2007]] ; [[#Messner--2015|Messner 2015]] ). This subsection is focused on an assessment of the emerging quantitative literature on global accelerated action pathways towards 1.5°C–2°C, which to a large extent abstracts from the underlying processes and uses a number of stylised approaches to generate these pathways. A representative of accelerated action pathways has been identified as one of the Illustrative Mitigation Pathways (IMPs) in this assessment ( ''IMP-GS'' , Figure 3.31).

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[[File:ceb4a9ca7f4f5083eb84dae4f7f24c8c IPCC_AR6_WGIII_Figure_3_31.png]]

'''Figure 3.31 |''' '''Comparison of (i) pathways with immediate action to limit warming to 2°C (&gt;67%) (Immediate, light blue), (ii) pathways following the NDCs until 2030 and limiting warming to 2°C (&gt;67%) thereafter (NDC; orange), and (iii) pathways accelerating near-term action until 2030 beyond NDC ambition levels and limiting warming to 2°C (&gt;67%) thereafter (accelerated) for selected indicators as listed in the panel titles, based on pathways from van Soest''' '''et al.''' '''(2021a).''' Low-carbon electricity comprises renewable and nuclear power. Indicator ranges are shown as box plots (full range, interquartile range, and median) for the years 2030, 2050 and 2100 (absolute values) and for the periods 2020–2030, 2030–2050 (change indicators). Ranges are based on nine models participating in [[#van%20Soest--2021a|van Soest et al. (2021a)]] with only seven models reporting emissions and climate results and eight models reporting carbon prices. The purple dot denotes the Illustrative Mitigation Pathway ''GS'' that was part of the study by van Soest et al.

One approach relies on augmenting initially moderate emissions-pricing policies with robust anticipation of ratcheting up climate action in the future ( [[#Spencer--2015|Spencer et al. 2015]] ). If announcements of strong future climate policies are perceived to be credible, they can help to prevent carbon lock-in as investors anticipating high future costs of GHG emissions would reduce investment into fossil fuel infrastructure, such as coal power plants ( [[#Bauer--2018b|Bauer et al. 2018b]] ). However, the effectiveness of such announcements strongly hinges on their credibility. If investors believe that policymakers could drop them if anticipatory action did not occur, they may not undertake such action.

Another approach relies on international cooperation to strengthen near-term climate action. These studies build on international climate policy architectures that could incentivise a coalition of like-minded countries to raise their mitigation ambition beyond what is stated in their NDC ( [[#Graichen--2017|Graichen et al. 2017]] ). Examples are the idea of climate clubs characterised by harmonised carbon and technology markets ( [[#Nordhaus--2015|Nordhaus 2015]] ; [[#Keohane--2017|Keohane et al. 2017]] ; [[#Paroussos--2019|Paroussos et al. 2019]] ; [[#Pihl--2020|Pihl 2020]] ) and the Powering Past Coal Alliance (PPCA) ( [[#Jewell--2019|Jewell et al. 2019]] ). [[#Paroussos--2019|Paroussos et al. (2019)]] find economic benefits of joining a climate club despite the associated higher mitigation effort, in particular due to access to technology and climate finance. [[#Graichen--2017|Graichen et al. (2017)]] find an additional reduction of 5–11 GtCO 2 -eq compared to the mitigation ambition in the NDCs from the successful implementation of international climate initiatives. Other studies assess benefits from international transfers of mitigation outcomes ( [[#Stua--2017|Stua 2017]] ; [[#Edmonds--2021|Edmonds et al. 2021]] ). [[#Edmonds--2021|Edmonds et al. (2021)]] find economic gains from sharing NDC emissions-reduction commitments compared to purely domestic implementation of NDCs. If reinvested in mitigation efforts, the study projects an additional reduction of 9 billion tonnes of CO 2 in 2030.

The most common approach relies on strengthening regulatory policies beyond current policy trends, also motivated by the finding that such policies have so far been employed more often than comprehensive carbon pricing ( [[#Kriegler--2018a|Kriegler et al. 2018a]] ; [[#Roelfsema--2018|Roelfsema et al. 2018]] ; [[#Fekete--2021|Fekete et al. 2021]] ; [[#IEA--2021a|]] [[#IEA--2021|IEA 2021]] a ; [[#van%20Soest--2021a|van Soest et al. 2021a]] ). Some studies have focused on generic regulatory policies such as low-carbon support policies, fossil fuel-sunset policies, and resource-efficiency policies ( [[#Bertram--2015b|Bertram et al. 2015b]] ; [[#Hatfield-Dodds--2017|Hatfield-Dodds et al. 2017]] ). [[#Bertram--2015b|Bertram et al. (2015b)]] found that a moderate carbon price combined with a coal moratorium and ambitious low-carbon support policies can limit efficiency losses until 2030 if emissions pricing is raised thereafter to limit warming to 2°C. They also showed that all three components are needed to achieve this outcome. [[#Hatfield-Dodds--2017|Hatfield-Dodds et al. (2017)]] found that resource efficiency can lower 2050 emissions by an additional 15–20% while boosting near-term economic growth. The International Energy Agency ( [[#IEA--2021a|]] [[#IEA--2021|IEA 2021]] a ) developed a detailed net zero scenario for the global energy sector characterised by a rapid phase-out of fossil fuels, a massive clean energy and electrification push, and the stabilisation of energy demand, leading to 10 GtCO 2 lower emissions from energy use in 2030 than in a scenario following the announced pledges.

The Paris Agreement has spurred the formulation of NDCs for 2030 and mid-century strategies around the world (cf. Chapter 4). This is giving researchers a rich empirical basis to formulate accelerated policy packages taking national decarbonisation pathways as a starting point ( [[#Graichen--2017|Graichen et al. 2017]] ; [[#Jiang--2017|Jiang et al. 2017]] ; [[#van%20Soest--2017b|van Soest et al. 2017b]] ; [[#Waisman--2019|Waisman et al. 2019]] ). The concept is to identify good practice policies that had demonstrable impact on pushing low-carbon options or reducing emissions in a country or region and then consider a wider roll out of these policies taking into account regional specificities ( [[#den%20Elzen--2015|den Elzen et al. 2015]] ; [[#Fekete--2015|Fekete et al. 2015]] , 2021; [[#Kriegler--2018a|Kriegler et al. 2018a]] ; [[#Kuramochi--2018|Kuramochi et al. 2018]] ; [[#Roelfsema--2018|Roelfsema et al. 2018]] ). A challenge for this approach is to account for the fact that policy effectiveness varies with different political environments in different geographies. As a result, a global roll out of good practice policies to close the emissions gap will still be an idealised benchmark, but it is useful to understand how much could be gained from it.

Accelerated action pathways derived with this approach show considerable scope for narrowing the emissions gap between pathways reflecting the ambition level of the NDCs and cost-effective mitigation pathways in 2030. [[#Kriegler--2018a|Kriegler et al. (2018a)]] find around 10 GtCO 2 -eq lower emissions compared to original NDCs from a global roll out of good practice plus net zero policies and a moderate increase in regionally differentiated carbon pricing. [[#Fekete--2021|Fekete et al. (2021)]] show that global replication of sector progress in five major economies would reduce GHG emissions in 2030 by about 20% compared to a current policy scenario. These findings were found in good agreement with a recent model comparison study based on results from nine integrated assessment models (IAMs) ( [[#van%20Soest--2021a|van Soest et al. 2021a]] ). Based on these three studies, implementing accelerated action in terms of a global roll out of regulatory and moderate pricing policies is assessed to lead to global GHG emissions of 48 (38–52) GtCO 2 -eq in 2030 (median and 5–95th percentile based on 10 distinct modelled pathways). This closes the implementation gap for the NDCs, and in addition falls below the emissions range implied by implementing unconditional and conditional elements of NDCs by 2–9 GtCO 2 -eq. However, it does not close the emissions gap to immediate action pathways that limit warming to 2°C (&gt;67%), and, based on our assessment in [[#3.5.2|Section 3.5.2]] , emission levels above 40 GtCO 2 -eq in 2030 still have a very low prospect for limiting warming to 1.5°C (&gt;50%) with no or limited overshoot.

Figure 3.31 shows the intermediate position of accelerated action pathways derived by [[#van%20Soest--2021a|van Soest et al. (2021a)]] between pathways that follow the NDCs until 2030 and immediate action pathways limiting warming to 2°C (&gt;67%). Accelerated action is able to reduce the abrupt shifts in emissions, fossil fuel use and low-carbon power generation in 2030 and also limits peak warming more effectively than NDC pathways. But primarily due to the moderate carbon price assumptions (Figure 3.31b), the reductions in emissions and particular fossil fuel use are markedly smaller than what would be obtained in the case of immediate action. The assessment shows that accelerated action until 2030 can have significant benefits in terms of reducing the mitigation challenges from following the NDCs until 2030. But putting a significant value on GHG emissions reductions globally remains a key element of moving onto 1.5°C–2°C pathways. The vast majority of pathways that limit warming to 2°C (&gt;67%) or lower, independently of their differences in near-term emission developments, converge to a global mitigation regime putting a significant value on GHG emission reductions in all regions and sectors.

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