Can the combination of urban development models promote carbon productivity? Evidence from an empirical analysis in China

The combination integration of urban development models (CUDM) emerges as pivotal in aligning economic development with achieving the “dual-carbon” goals. However, existing studies often overlook CUDM's potential for carbon emissions reduction. Multi-period DID models exhibit excellent performance in mitigating endogeneity and eliminating omitted variables. This study examines the impact of the combination integration of innovative and smart city development models (CISDM) on urban carbon productivity, employing a multi-period DID model with data spanning 2006–2019 from Chinese cities. The results indicate that: (1) CISDM significantly enhances urban carbon productivity by 0.2064 units, primarily driven by innovation-induced technological advancements and structural effects. (2) CISDM yields a significant synergistic effect on urban carbon productivity. Compared to single pilot cities, CISDM significantly increases a city's carbon productivity by 0.1854 units. This effect is particularly noticeable when prioritizing “smart” initiatives over innovation. (3) The effect of the CISDM on carbon productivity varies according to city characteristics. While environmental regulations amplify CISDM's positive impact, resource-based cities struggle to harness its effective. This study underscores the potential of leveraging CUDM to promote "dual-carbon" objectives, providing valuable insights for policy synergies.