Has the synergistic development of urban cluster improved carbon productivity? --Empirical evidence from China

As urbanization has developed, a variety of urban clusters have gradually emerged with important effects on regional economic growth and carbon emissions. This paper constructs a multi-period difference-in-difference (DID) model for testing how urban cluster synergistic development policy (UCSDP) affects urban carbon productivity in 148 cities of China with 13 urban clusters as the experimental group from 2003 to 2019. According to the results, the UCSDP improves carbon productivity, mainly via reducing energy intensity. In addition, UCSDP improves carbon productivity by adjusting energy structure, increasing green innovation, altering city greening levels, and accelerating the process of urbanization. Moreover, it can produce synergistic effects in terms of energy structure, green innovation, greening level, and urbanization level. Furthermore, the UCSDP has heterogeneous effects on the carbon productivity in various cities. Specifically, the carbon productivity of highstatus, high-rank, and resource-based cities responds more significantly to UCSDP. Therefore, policymakers should strengthen the integration of urban clusters, offer targeted development suggestions for different cities, modify the energy and greening structure, accelerate the process of urbanization, and focus on the formulation of reasonable environmental regulation policies.