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• Framework links carbon goals with resident well-being in megacities. • Develop NCSE indicator integrating carbon sinks, emissions and ecosystem services. • Only 13.73 % of subdistricts have high NCSE in their green spaces. • Small, dispersed green spaces show higher per-unit ecological efficiency. • UGS efficiency improves with better land-use mix and greenway networks. Amid the global climate crisis, urban green spaces (UGS)—as composite ecosystems with both carbon sink and social service functions—have become vital strategic assets for reducing urban carbon emissions and enhancing residents’ well-being. In the context of increasingly constrained resources, this study systematically investigates the role of UGS in advancing carbon neutrality from an eco-social perspective, aiming to improve the efficiency of greening allocation. To this end, a novel net carbon sink efficiency (NCSE) indicator integrating ecosystem services was developed, forming a comprehensive evaluation framework that balances carbon sequestration enhancement, ecosystem service optimization, and resource input minimization. Using 102 subdistricts in downtown Shanghai as the study area, the super-slack-based measure (Super-SBM) model with undesired output was applied to assess NCSE, while the Tobit regression model identified key influencing factors, including built environment characteristics and spatial patterns of UGS. Key findings include: (1) Periphery subdistricts exhibited higher overall UGS output capacity, but dispersed small green spaces in the center showed superior per-unit efficiency. (2) Only 14 subdistricts (13.73%) have achieved effective NCSE, while most show low efficiency and need to be enhanced. (3) Based on NCSE and proximity to the city center, subdistricts can be classified into four types: center-efficient, peripheral-efficient, center-inefficient, and peripheral-inefficient. (4) Factors such as functional land-use mix, road network density, watershed area proportion, and greenway and pocket park development significantly improved NCSE. This integrated assessment framework links macro-level low-carbon policy with micro-level urban well-being, offering a transferable model for sustainable green infrastructure planning in global megacities.
Song et al. (Fri,) studied this question.