The impact of regional integration in the Yangtze River Delta on urban carbon emissions

The Yangtze River Delta is a demonstration area for China's high-quality integrated development and an important area for China to achieve its peak dioxide emissions by 2030 and carbon neutrality targets by 2060. In the context of the transformation of China's administrative region economy to an integrated economy, the regional integration of the Yangtze River Delta has reduced administrative barriers and optimized the allocation of factors. At the same time, what impact does it have on urban carbon emissions? Based on the panel data of prefecture level and above cities in China, this paper regards the issuance of The Regional Planning of Yangtze River Delta as a quasi-natural experiment, using the difference-in-difference (DID) method to estimate the effects of regional integration in the study area on urban carbon emissions. Furthermore, by using the mediation effect model, we identify the possible internal mechanism of regional integration on carbon emission effects. The results showed that regional integration policy of this delta in 2010 significantly reduced urban carbon emissions, and after a series of robustness tests such as the parallel trend test, PSM-DID and placebo test were still true. From the perspective of dynamic effects, the carbon emission reduction effect appeared in the third year after the issuance of regional integration policy. At the same time, compared with general hierarchy cities, regional integration had a greater effect on carbon emissions reduction of high hierarchy cities. Mechanism verification showed that regional integration policy aggravated urban carbon emissions through the strengthening of economic links between cities, and reduced urban carbon emissions by promoting the upgrading of the industrial structure and the improvement of urban technology. From the perspective of better achieving the goal of high-quality integration in the Yangtze River Delta, it is suggested that the delta should actively explore the cooperation mechanism of carbon emission reduction and green development between cities, and establish a green development evaluation index system that can be monitored and operated. Besides, we should focus on the green transformation of industries and increase investment in green technology research and development among cities in the Yangtze River Delta.