Impact of digital-green policy synergy on urban green innovation: empirical evidence from a double machine learning model

Under the dual context of digital economy and green economy, it is imperative to examine the effects of digital-green policy synergy, represented by Broadband China Demonstration City policy and Low-Carbon City Pilot policy, on green innovation. Utilising panel data spanning from 2011 to 2021 across 279 prefecture-level cities in China, this research utilises a dual machine learning framework to evaluate multidimensional policy effects of digital-green policies on green innovation. The results demonstrate that: (1) digital-green policies markedly increase urban green innovation, with the synergistic effect of dual pilot policies being more pronounced than that of a single pilot policy; (2) digital-green policies promote green innovation by optimising economic structures and strengthening environmental regulations; (3) beneficial impact of digital-green policies on green innovation is more evident in eastern cities, non-resource-based cities, highly marketized cities, and cities with strong intellectual property protection. These conclusions provide theoretical insights and policy implications for fostering urban green innovation, considering policy synergy.