Mechanisms and spatial effects of digital industry agglomeration on urban carbon emission intensity

Digital industry agglomeration significantly influences urban low-carbon development, with environmental effects that differ across agglomeration stages. This study analyzes panel data from 280 Chinese prefecture-level cities spanning 2009 to 2023 to assess the impact of digital industry agglomeration on urban carbon emission intensity. The empirical approach integrates nonlinear panel regressions, a nonlinear mediation model, and a spatial Durbin model to identify nonlinear, mediating, and spatial effects. The findings reveal a pronounced inverted U-shaped relationship between digital industry agglomeration and urban carbon emission intensity. Additionally, digital industry agglomeration exhibits a U-shaped effect on green technological innovation, indicating that the innovation effect initially weakens and subsequently strengthens as agglomeration deepens, thereby generating stage-dependent indirect effects on carbon emission intensity through the green patent channel. Spatial marginal effects also display nonlinear variation with the degree of digital industry agglomeration. At lower agglomeration levels, the total spatial marginal effect is positive, indicating increased carbon emission intensity across the regional system. As agglomeration intensifies, the total effect diminishes and ultimately becomes significantly negative, indicating a transition towards cross-regional emissions reduction. These results offer policy-relevant insights for designing low-carbon strategies tailored to different stages of digital industry agglomeration and for enhancing cross-regional coordination.