Synergistic impacts of carbon emission trading policy and innovative city pilot policy on urban land green use efficiency in China

Reducing the conflict between economic expansion and environmental conservation requires green-based innovation policies. The synergistic impacts of these policies on promoting urban land green use efficiency (ULGUE) remain underexplored. Utilizing panel data from 285 prefecture-level cities in China (2006-2020), we apply the super-efficiency slacks-based measure (SBM) to calculate ULGUE. Employing the staggered difference-in-difference (SDID) model and mediation model, we investigate the synergistic effects of the Carbon Emissions Trading Policy (CETP) and the Innovative City Pilot Policy (ICPP), along with their influencing mechanisms on ULGUE. The results demonstrate that the average ULGUE keeps increasing from 2006 to 2020 and the simultaneous implementation of CETP and ICPP enhances ULGUE, with a more pronounced effect when CETP precedes ICPP. The concurrent implementation of dual policies boosts ULGUE by leveraging technological innovation and industrial structure as mediators. The magnitude of the mediating effect is as follows: green innovation > general innovation > rationalization of industrial structure > advancement of industrial structure. We also observe heterogeneous synergistic impacts of CETP and ICPP on ULGUE, with greater effectiveness in non-resource-based and large-scale cities. These results offer valuable insights for crafting effective policy combinations to advance sustainable development trajectories for China and other developing countries.