Synergistic Efficiency and Spatiotemporal Differentiation of Pollution Reduction, Carbon Mitigation, Ecological Expansion, and Economic Growth

The conventional “resources–energy–environment–economy” growth paradigm has imposed severe environmental pressures on China, including land desertification and smog pollution. In the context of carbon peaking and carbon neutrality, the synergistic advancement of pollution reduction, carbon mitigation, ecological expansion, and economic growth (PCEG) has become a critical development pathway. Drawing on Pareto improvement theory, this study applies a super-efficient slack-based measure (SBM) model to evaluate PCEG synergistic efficiency across 30 Chinese provinces from 2003 to 2020. We further investigate its temporal evolution, regional heterogeneity, and convergence characteristics. The empirical results reveal that (1) PCEG synergistic efficiency follows a U-shaped trajectory; (2) both technological change and efficiency change contribute positively to post-2018 recovery; (3) substantial regional heterogeneity and cross-regional overlap are observed, with intra-regional disparities playing an equally important role in shaping overall inequality as inter-regional differences; and (4) no σ-convergence is observed at the national or regional level; β-convergence is significant in the non-spatial setting but drops sharply once spatial dependence is incorporated, indicating that administrative barriers, market segmentation, and frictions in factor mobility hinder the convergence process. These results inform a policy mix that addresses within-region heterogeneity, sustains the post-2018 momentum of technological progress, and dismantles spatial barriers to factor mobility.