Driving urban low-carbon transition in China: The role of innovation-openness policy mix

Balancing economic growth and ecological protection is key to achieving the UN Sustainable Development Goals (SDGs), yet single policies often fail in low-carbon transitions. This study utilizes panel data from 251 Chinese cities (2006–2022) and employs a double machine learning (DML) approach to assess whether the policy mix of innovation and openness exerts a synergistic effect on the economic low-carbon transition. The results indicate that innovation and openness significantly promote economic low-carbon transformation; the combined effect of innovation and openness exceeds the sum of their individual effects by 7.91%. Notably, the effect of openness policy shifts from insignificant when implemented alone to significant when combined with innovation policy, with the combined policy effect reaching 101.08% of the effect of innovation policy alone. These findings remain robust after a series of sensitivity tests and addressing endogeneity concerns. Mechanism analysis reveals that innovation and openness synergistically drive economic low-carbon transformation by expanding foreign investment creation, fostering green innovation agglomeration, and promoting industrial upgrading. Cross-sectional analysis shows that the synergistic effect is more pronounced in eastern and non-resource-based cities in China. In summary, innovation and openness constitute a synergistic policy mix that effectively promotes economic low-carbon transformation, offering valuable insights for other economies seeking to advance their own low-carbon transitions. Specifically, this synergistic effect not only drives the decoupling of economic growth from carbon emissions but also directly contributes to carbon emission reduction, laying a solid foundation for achieving global climate goals.