The impact of national-level urban agglomeration construction on the synergistic development of carbon reduction and growth and its policy implications

The construction of national-level urban agglomerations, as a key strategic layout for regional development, serves as a vital engine driving the transition to a low-carbon economy. Based on panel data from 282 cities spanning the years 2009 to 2023, this study employs a progressive difference-in-differences model to examine the impact of national-level urban agglomeration construction on the synergistic development of carbon reduction and economic growth. It further explores the distance decay effect from the "core-periphery" perspective. The results indicate that: (1) The construction of national-level urban agglomerations can significantly and robustly promote the synergistic development of carbon reduction and economic growth, while also facilitating collaborative emissions reduction and common prosperity. (2) The synergistic effects of carbon reduction and growth achieved through national-level urban agglomeration construction are realized via two main channels: urban linkage (enhancing economic connectivity, optimizing functional division, and driving market integration) and urban development (alleviating resource misallocation, promoting green innovation, and advancing industrial upgrading). (3) The synergistic effects of carbon reduction and growth resulting from national-level urban agglomeration construction exhibit heterogeneity across urban agglomerations at different developmental stages, as well as across cities with varying locations and hierarchical ranks. (4) The natural, administrative, and socio-cultural barriers between peripheral cities and core cities can weaken the synergistic effects of carbon reduction and growth brought about by the construction of national-level urban agglomerations.