Editing IPCC:AR6/WGIII/Chapter-13 (section)

=== 13.5.3 Performance and Global Mitigation Impact ===

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The performance of sub-national actors’ mitigation policies have been measured using criteria such as existence of mitigation targets, incentives for mitigation, definition of a baseline, and existence of a monitoring, reporting, and verification procedure ( [[#Hsu--2019|Hsu et al. 2019]] ). Existing evaluations range from small-scale studies assessing the mitigation potential of commitments by sub-national regions, cities and companies in the USA or in 10 high-emitting economies ( [[#Roelfsema--2017|Roelfsema 2017]] ; [[#Hsu--2019|Hsu et al. 2019]] ), to larger studies finding that over 9149 cities worldwide could mitigate 1400 MtCO 2 -eq in 2030 ( [[#Global%20Covenant%20of%20Mayors%20for%20Climate%20and%20Energy--2018|Global Covenant of Mayors for Climate and Energy 2018]] ; [[#Hsu--2018|Hsu et al. 2018]] , 2019). These sub-national mitigation potential estimates vary since a range of approaches exists for accounting for overlaps between sub-national governments and their nested jurisdictions (e.g., states, provinces, and national governments) ( [[#Roelfsema--2018|Roelfsema et al. 2018]] ; [[#Hsu--2019|Hsu et al. 2019]] ). One analysis found that the cities of New York, Berlin, London, Greater Toronto, Boston, and Seattle have achieved on average a 0.27 tCO 2 -eq per capita per year reduction ( [[#Kennedy--2012|Kennedy et al. 2012]] ). [[#Hsu--2020c|Hsu et al. (2020c)]] found that 60% of more than 1000 European cities, representing 6% of the EU’s total emissions, are on track to achieving their targets, reducing more than 51 MtCO 2 -eq. While evidence is limited, there are concerns that implementation challenges persist with city level plans, particularly tied to management of initiatives and engagement of the population ( [[#Messori--2020|Messori et al. 2020]] ).

Whether participation in transnational climate initiatives impacts sub-national governments’ achievement on climate mitigation goals is uncertain. Some find that higher ambition in climate mitigation commitments did not translate into greater mitigation ( [[#Kona--2016|Kona et al. 2016]] ; [[#Hsu--2019|Hsu et al. 2019]] ). Other studies associate participation in networks with increased solar photovoltaic systems (PV) investment ( [[#Khan--2016|Khan and Sovacool 2016]] ; [[#Steffen--2019|Steffen et al. 2019]] ), and with potential to achieve carbon emissions reductions per capita in line with a global 2°C scenario ( [[#Kona--2016|Kona et al. 2016]] ).

Reporting networks may attract high-performing actors, suggesting an artificially high level of cities interested in taking climate action or piloting solutions (self-selection bias) that may not be effective elsewhere (van der Heijden 2018). Many studies present a conservative view of potential mitigation impact because they draw upon publicly reported mitigation actions and exclude sub-national actions that are not reported ( [[#Kuramochi--2020|Kuramochi et al. 2020]] ).

In addition to direct mitigation contributions, climate action partnerships may deliver indirect effects that, while difficult to quantify, ensure long-term change ( [[#Chan--2015|Chan et al. 2015]] ). Experimentation and policy innovation helps to establish best practices ( [[#Hoffmann--2011|Hoffmann 2011]] ); set new norms for ambitious climate action that help build coalitions ( [[#Chan--2015|Chan et al. 2015]] ; [[#Bernstein--2018|Bernstein and Hoffmann 2018]] ); and translate into knowledge sharing or capacity building ( [[#Lee--2012|Lee and Koski 2012]] ; [[#Hakelberg--2014|Hakelberg 2014]] ; [[#Purdon--2015|Purdon 2015]] ; [[#Acuto--2016|Acuto and Rayner 2016]] ). Emergent researchexplores whether, in addition to realising outcomes, mitigation initiatives also provide the resources, skills and networks that governments and other stakeholders currently use to target other development goals ( [[#Shaw--2014|Shaw et al. 2014]] ; [[#Wolfram--2016|Wolfram 2016]] ; [[#Wiedenhofer--2018|Wiedenhofer et al. 2018]] ; [[#Amundsen--2018|Amundsen et al. 2018]] ; [[#Heikkinen--2019|Heikkinen et al. 2019]] ).

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