How does regional integration affect CO 2 emission intensity? A natural experiment based on the expansion of the Yangtze River Delta, China

Regional integration effectively promotes the coordinated development of the economy and society in urban agglomerations. However, existing studies have paid little attention to the effect of regional integration on low-carbon development. To address this research gap, this study takes the expansion of the Yangtze River Delta implemented in 2010 as a natural experiment to explore the impact of regional integration on carbon dioxide (CO 2 ) emission intensity by applying the differences-in-differences approach. Then, the mediating effect and moderating effect models are employed to investigate the influencing mechanisms involved. The results reveal that regional integration is positively correlated with CO 2 emission intensity. In other words, the rising degree of regional integration cannot facilitate carbon emission reduction in China. According to the mechanism analysis, regional integration will indirectly increase CO 2 emission intensity by strengthening economic connections among cities, while regional integration significantly reduces CO 2 emission intensity through improving technological innovation. Furthermore, the moderating effect of industrial structure upgrading appears trivial in the Yangtze River Delta as a whole. The rationale is that the incumbent cities may optimize their industrial structure by transferring energy-intensive and high-polluting industries to the newly added cities. Finally, based on the above findings, this study offers several solid policy implications for promoting coordinated environmental governance.