Polycentricity or monocentricity? A multi-scale assessment of how urban agglomeration structures influence carbon emission performance in China

Global warming driven by persistent carbon emissions has made emission reduction a pressing research focus. Understanding how urban agglomeration spatial structures influence carbon emission performance is essential for developing effective mitigation strategies. This study examines 13 urban agglomerations in China from 2006 to 2020. A two-dimensional framework is proposed to capture spatial structure, encompassing both morphological and functional dimensions. A Geographically and Temporally Weighted Regression model is employed at both the city and county scales. The results indicate that: (1) Spatial morphological structures show a general trend toward monocentricity at both scales. (2) Functional structures become increasingly monocentric patterns at the city scale while remaining relatively stable at the county scale. (3) Carbon emission performance has improved overall, yet interregional disparities have widened. (4) The influence of spatial structure on carbon emission performance shows significant structure type and scale-dependent characteristics. At the city scale, the polycentricity of spatial morphological and functional structures is unstable in its direction of influence and lacks consistency. In contrast, at the county scale, morphological polycentricity continues to inhibit carbon emission performance, while functional polycentricity continues to promote performance enhancement. (5) Most control variables significantly affect carbon performance at city and county scales, but these effects' direction, strength, and temporal pattern vary across scales. These results provide new insights into the spatial mechanisms underlying low-carbon development and offer a theoretical basis for designing targeted emission reduction strategies tailored to varying spatial structures and governance contexts.