Impact of low-carbon city pilot policies on urban green innovation from the perspective of spatial and temporal heterogeneity

The low-carbon city pilot policy (LCPP) in China is an active response to climate change, with cities serving as the main agents of action. Enhancing green innovation at a city-wide level can effectively support the promotion of pilot cities' efforts towards sustainable growth. Using panel data from 204 prefectures collected from 2005 to 2019, we adopted the time-varying difference-in-differences (DID) model and the spatial Durbin model combined with time-varying DID (SDM-DID) to determine the impact of the LCPP on urban green innovation and its temporal and spatial heterogeneity. Empirical findings showed that (1) LCPP had a significant positive impact on urban green innovation, and green invention patents had a greater green innovation effect than green utility model patents. (2) Heterogeneity analysis revealed that in terms of geographical location, the pilot policy was more effective in promoting urban green innovation in the eastern and central regions in comparison to the western region. At the city level, the pilot policy had a greater impact on green innovation in first- and second-tier cities. With regard to city scale, large-scale cities showed a greater impact on green innovation than small- and medium-sized cities. (3) Mechanistic testing revealed that LCPPs stimulated urban green innovation by talent aggregation, increasing government support for innovation, and public participation; but the mechanism for alleviating financing constraints has yet to be effectively validated. (4) The LCPP showed a spatial spillover effect, whereby one city's low-carbon governance yielded institutional dividends for neighboring cities both geographically and economically, and the impact was more pronounced in those cities that were not resource-based. This study presents empirical evidence at the urban and spatial levels, supporting the comprehensive promotion of low-carbon city construction and development in China.