Progress and performance in synergizing the reduction of pollution and carbon emissions in China from 2015 to 2022

As the world confronts the dual crises of environmental pollution and climate change, China—one of the largest developing economies—faces particularly urgent demands for coordinated action. However, systematic frameworks for tracking cross-sector progress in pollution and carbon co-control remain underexplored. Here, we propose the Index for Synergies in Environmental protection and Carbon reduction (ISEC)—a nationwide, multidimensional system that integrates status and progress indicators using observation-based evidence. The ISEC framework includes three core dimensions: Synergetic Effect, Synergetic Action, and Synergetic Management, each with specific indicators reflecting the interplay between pollution reduction and decarbonization efforts. We apply ISEC to assess China's pollution–carbon co-control performance from 2015 to 2022 at both national and provincial scales. Our results show that China's national ISEC score rose by 53.9% over the study period, reflecting substantial gains in coordinated pollution and carbon reduction. At the provincial level, marked regional disparities remain: economically developed regions with stronger environmental capacity, such as Beijing, Shanghai, and the southeast coast, consistently demonstrate higher synergy levels, whereas resource-dependent regions in northern and western China (e.g., Inner Mongolia, Ningxia, Xinjiang) continue to face severe challenges. These findings underscore the importance of promoting continuous structural transformation and implementing differentiated, region-specific policies in the future. ISEC offers a transferable and flexible tool for monitoring synergy across various levels and policy contexts, offering valuable insights for China and other developing economies aiming for coordinated environmental and climate governance.