Mitigation potential of subnational actors: The subnational wedge

While nearly 11,000 city and regional governments worldwide had articulated some form of climate action plan or target as of May 2025, only 2,859 cities and 177 regions within G20 countries had quantifiable mitigation pledges [3,4]. From this quantified subset, we estimate the "subnational wedge:" the share of the global mitigation gap that these city and regional pledges could close, assuming full implementation. We focus on the G20 since subnational governments within these countries constitute the majority of available data; therefore, our assessment represents likely an underestimation of the full subnational mitigation wedge due to data availability. Aggregated across these jurisdictions using methods established in prior work [5,6], we find that, if fully implemented, their targets imply mitigation potential of approximately 3.4 to 3.8 GtCO2e in 2030 and 7.1 to 7.8 GtCO2e in 2050. This estimated range reflects different asumptions regarding overlap between city and regional pledges. The upper bound estimate (Fig 1) allows for potential non-overlap between city and regional emissions coverage, while a lower-bound estimate assumes complete emissions overlap between regions and cities (Fig A in S1 Appendix).

This distinction matters because geographic overlap is not the same as emissions overlap. While we identified territorial overlap in approximately 2,000 entities, a closer look at sectoral coverage shows that spatial overlap rarely implies redundant emissions coverage. Across matched region-city pairs with territorial overlap, sectoral emissions coverage differs in at least 67% of cases; 32% of pairs have insufficiently-reported sectoral coverage, and only 1% have complete sectoral alignment.

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Fig 1. Mitigation potential, without overlap, of cities (in red) and regions (in gold) in 2030 and 2050 for the G-20 and selected countries.

Potentials are calculated compared to current national policy scenarios and national emissions determined by the Climate Action Tracker (2025), which also provides the emissions reductions required for 1.5 °C-compatible pathways.

https://doi.org/10.1371/journal.pclm.0000921.g001

This near-term 2030 wedge is substantial in both absolute and comparative terms: it exceeds the emissions of the entire U.S. energy sector [7] and would close roughly 25% of the 2030 1.5 °C emissions gap (i.e., the difference between the projected 2030 emissions under current policies and a 1.5 °C-consistent pathway). This potential is not evenly distributed, with largest 2030 mitigation contributions coming from cities and regions in China (~1.63 GtCO2e), the United States (~0.83 GtCO2e) and the European Union (~0.32 GtCO2e), highlighting the dual importance of major advanced economies and rapidly urbanizing emerging economies in shaping global subnational mitigation potential. Notably, although U.S. city and regional ambition has expanded since 2023 [6], even full realization of these pledges by 2030 would still deliver only about 25% of the reductions required for the United States to remain on a 1.5 °C-aligned national pathway.

Extending our analysis to 2050 using linear interpolation between base-year emissions, intermediate self-reported points, and target-year values and by assuming emissions remain constant after the target year, we find that the subnational wedge is both persistent but structurally limited. Estimated mitigation potential in 2050 substantially exceeds 2030 levels (Fig 1), reflecting the rapid diffusion of net-zero and other high-ambition endpoints across subnational targets, with the exception of the EU. For example, 2050 potential reaches 1.81 GtCO2e and 3.55 GtCO2e in the US and China respectively. While G20 subnational mitigation potential grows over time, it still represents only about 20% of the emission reductions required to move from a 2050 current-policy trajectory to a 1.5 °C-consistent pathway according to the UNEP 2025 Emissions Gap Report. What this indicates is that the subnational wedge expands in size but never accounts for more than one-third of the required transition, highlighting both the magnitude of the opportunity and the limits of solely relying on subnational action. Finally, when exploring the absolute emissions and emissions per capita trajectories for each country, we observe that most countries, except both regions and cities, show a steeper trajectory between 2022 to 2030 than in the period of 2030 to 2050 (Fig B and Fig C in S1 Appendix), indicating that on a per capita basis, the most impactful reduction would happen towards the year 2030.

Ambition without pace: A dual deficit in subnational delivery

Despite the growing momentum in planning and target-setting, subnational climate governance is currently constrained by a dual deficit of ambition and implementation: targets have proliferated, but the pace of real-world emission cuts are too slow. To assess delivery, we focus on the subset of targets for which sufficient emissions data exist to evaluate real-world trajectories. Specifically, for 2,105 targets pledged by 1,542 entities, we have adequate baseline and inventory emissions to track progress over time.

Yet city and regional governments are on track (defined as when its actual per capita emissions reduction in the inventory year meets or exceeds the target per capita emissions in the target year [8]) to achieve only around one-third (38%) of short-term targets and a slightly lower percentage (35%) of long-term targets; mid-term targets (7–16 years) perform worst, with fewer than 29% currently on track (Fig 2). Baseline emissions do not explain this gap: the median baseline emissions are nearly the same for places on track and those that are not (the difference is around 0.01MtCO2e). Instead, differences emerged in target design. Cities or regions that are on track tend to adopt more moderate percentage reduction values and near-term reduction commitments typically within six years, suggesting a stronger alignment between target setting and implementation capacity. Taken together, these patterns show a lack of temporal credibility in subnational climate governance: mid- and long-term endpoints are rarely backed by near-term reductions consistent with required global mitigation goals.

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Fig 2. On and off-track city and region targets segmented according to time frame (i.e., short, mid, and long-term) and by ambitions of reduction.

https://doi.org/10.1371/journal.pclm.0000921.g002

The pace at which emissions are actually falling helps explain these shortfalls. As Fig 3 indicates, the median annualized reduction across all evaluated entities is 1.39% per year, which is around half of the 2.65% per year required for the subnational portfolio to be collectively on track, and well below the ~5% annual reductions needed for 1.5 °C-consistent trajectories [9]. Among entities that are on track, the top decile with the steepest reduction rates is concentrated largely in Europe. Cities and regions in other high-income nations, including Canada, Belgium, and the United States, together account for more than 27% of evaluated targets, yet fewer than one-third show measurable progress. This pattern suggests that, in several high-income, high-emitting countries, ostensibly ambitious targets are undercut by insufficient implementation, eroding the temporal credibility of the subnational wedge.

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Fig 3. Distribution of annualized emissions reductions between a subnational actor’s base year and their most recent inventory year.

Actual average reductions are indicated in the green dashed line, required reductions for all cities and regions to stay on track are in the purple dashed line.

https://doi.org/10.1371/journal.pclm.0000921.g003

Differences in ambition further compound the delivery challenge. Fig 2 shows that a slightly higher share of on-track targets falls within the low-ambition category (~44%), and that low ambition, defined here as annual emissions reductions below 1.74 tons, predominates across all time frames. For cities, short-term targets remain the largest share within every ambition tier (about 67% of city-level targets), and regional targets show an even stronger short-term skew; regional mid-term targets are especially weak, with only one currently on track.

Collecitvely, these findings point to a dual deficit of ambition and implementation in subnational climate governance. Consistent with earlier stocktakes [6,8], only 37% of evaluated subnational governments are on track to meet their mitigation goals. Closing this dual deficit requires a step-change in delivery: cities and regions would need to roughly double the current pace of emissions reductions (to ~2.7% annually) to meet existing targets, and more than triple it to align with a 1.5 °C-consistent pathway [9].

A multilevel delivery architecture for the subnational wedge

The evidence presented here points to a dual imperative. On the one hand, subnational commitments already constitute a material mitigation wedge for Paris-aligned pathways, with quantified G20 city- and region-level targets capable of closing roughly 30% of the 2030 gap if fully delivered. On the other hand, the credibility of that wedge is constrained by an implementation deficit: only 37% of evaluated targets are on track, and current reduction rates are about half of what is required for collective alignment. The immediate question is therefore not whether subnational action matters, but how to embed this subnational wedge in an institutional setting that can reliably turn it into real emission cuts.

Achieving this shift will require a stronger multilevel “delivery architecture,” meaning the ensemble of financial, legal-institutional and networked capacities that connect local climate plans to durable investment and policy change across scales of governance. Its role is both stabilizing and catalytic: to buffer progress against capricious national political cycles and macro-geopolitical shocks, and to create channels through which successful local experiments [10] can scale and reshape expectations in national and international arenas. COP30 marked a concrete step in that direction: the Brazilian Presidency reaffirmed the Coalition for High Ambition Multilevel Partnership (CHAMP) to embed subnational governments within national climate policy and finance, including explicit integration into the next round of near-term NDCs and associated investment frameworks. This announcement builds on the latest round of NDC updates, in which more than half contain ‘strong’ urban content according to the latest UN Habitat report, with 73% proposing at least one urban mitigation option [11].

Operationalizing this multilevel turn now hinges on three complementary moves. First, subnational governments continuously cite inadequate financing and uncertainty over viable financing pathways as central barriers to implementing ambitious climate action plans [12,13]. Meeting this challenge requires efforts at multiple levels ranging from facilitating local government access to multilateral funds, fiscal decentralization at the national level, and blended-finance mechanisms that leverages public capital, which can be used strategically to scale investable subnational pipelines, particularly in high emission urban sectors such as power, buildings, and transport [11,14]. Particularly in the U.S. context, where federal support for local climate action has all been repealed, cities and states will need greater creativity and partnerships to secure necessary support to implement climate plans.

Second, subnational governments must prioritize embedding climate policies in ways that enhance their durability and resilience to political turnover. Research on policy entrenchment suggests that climate actions are more likely to persist when they create positive feedback loops through institutional design [15], economic path dependencies or co-benefits [16], and stakeholder coalitions. Cities that have successfully embedded durable climate policies have combined statutory mandates (e.g., building performance standards) with economic incentives (e.g., green procurement policies) and cross-sectoral integration that makes clear climate action’s co-benefits for mobility and transport, jobs and public health.

Finally, subnational and multilevel networks, both within the UN system and across international climate initiatives, have a critical role to play in strengthening horizontal capacity. These platforms can deepen peer learning and technical cooperation among cities and regions, with a stronger emphasis on meeting already-established mitigation targets. To date, many networks have focused primarily on disclosure and climate-planning processes. Future support should pivot towards bolstering subnational means of implementation, including institutional, technical, and financial capacities, particularly as their efforts become more critical to support national governments’ NDCs and global climate mitigation efforts. While there has been a gradual shift from purely project-based support towards climate finance and capacity-building initiatives, further efforts are needed to move beyond isolated projects and instead embed subnational climate action in substantive public policy frameworks.

Subnational governments clearly have potential to fill gaps in ambition left by national governments, but this wedge will remain largely symbolic if the dual deficit of ambition and implementation persists. Realizing it depends on building a multilevel delivery architecture rooted not only in national policy but also in regional and transnational coalitions that can provide political support, technical knowhow and finance to help local governments weather domestic volatility and broader geopolitical shocks. Of course, these tenets of a delivery architecture are not necessarily equivalent in their catalytic potential, and they most certainly interact and reinforce each other. Evidence suggests that subnational climate action plans that integrate cross-sector measures (e.g., energy efficiency), have clear leadership with community buy-in, and are backed by credible investment plans tend to be associated with higher ambition and stronger implementation results [8,17–19]. Whether subnational actors become a longstanding pillar of global decarbonization will depend on how the multilevel climate governance ecosystem matures to embed the subnational wedge into credible emission cuts.

Supporting information