High-speed rail and city's carbon productivity in China: a spatial difference-in-differences approach.

Improving carbon productivity is an important measure to promote low-carbon development. Since high-speed rail (HSR) has both economic and environmental effects, it is particularly important to clarify the relationship between HSR development and carbon productivity. In this paper, 285 cities in China from 2007 to 2017 are used as a research sample, and the relationship between the opening of HSR and the city's carbon productivity is studied using the spatial difference-in-difference method (SDID). The result shows that due to the intermediary effect of technological innovation and industrial structure, the opening of HSR significantly increases urban carbon productivity. At the same time, this influence has a significant positive spatial spillover effect. On average, when a city opens HSR, the local carbon productivity increases by 5.18%, and the carbon productivity of its neighboring cities increases by 13.52%. Overall, the positive effect of HSR on carbon productivity is more pronounced in the middle and western regions. However, the spatial spillover effect in the eastern region is significantly negative. These findings help to accurately assess the social benefits of HSR network expansion and provide important decision-making references for climate governance in the HSR era.