The spatial synergy of human and social capital mitigating CO2 emissions in Iranian provinces

Abstract This study investigates the direct, spatial spillover, and total effects of human capital, social capital, and their interaction on CO 2 emissions across 28 Iranian provinces over 2005–2020. Employing a dynamic Spatial Durbin Model (SDM) within an extended STIRPAT framework, the study accounts for temporal persistence, spatial interdependence, and the interaction between the two forms of intangible capital. The results show that both human capital and social capital have significant negative effects on CO 2 emissions, with human capital exhibiting a relatively stronger effect. Spatial spillover effects of both capitals are substantially larger than their direct effects, indicating environmental benefits extend beyond provincial boundaries through knowledge diffusion, social norms, and institutional learning. The interaction between human and social capital is also negative and significant, suggesting complementarity between the two forms of capital. Conditional marginal effects demonstrate that emission-reducing effects are consistently stronger in the long run than in the short run. The study contributes to the literature by integrating human and social capital within a dynamic spatial framework, explicitly identifying their interaction, and decomposing effects into direct and cross-provincial spillover components. These findings highlight the importance of coordinated regional strategies that promote interprovincial knowledge and technology diffusion while simultaneously strengthening education, skills, social trust, and civic participation.