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Cities and subnational governments are establishing their own mitigation targets and plans toward net-zero goals, yet the mitigation pathways used to assess decarbonization scenarios have been too coarse to directly evaluate urban action. Here, we develop a policy-compatible framework that links global mitigation pathways from the IMAGE integrated assessment model (IAM) under a SSP2, a middle-of-the-road socioeconomic pathway, to dynamic administrative urban units through a Kaya-based downscaling approach. We find that urban areas account for most modeled emissions reductions under both Current Policies and 2℃ pathways, and they dominate the transition to net-negative emissions by the end of the century. Using an administrative boundary approach, we estimate that more than four-fifths of global emissions already occur in urban areas, with this share remaining high across regions and scenarios despite substantial and variable spatial restructuring over time. Benchmarking 3,526 subnational climate targets across the G20 reveals an uneven landscape of subnational mitigation policy ambition across countries. Compared to 2020 levels, the collective urban-pledge trajectory implies a 3.4% increase in emissions by 2030 under the 2℃ benchmark, followed by a 75% decline by 2050, while under the Current Policies scenario they increase by 5.2% before declining by 40% by 2050.