City Diplomacy as a Green Strategy? International Sister City Partnerships and Urban Decarbonization

ABSTRACT The establishment of international sister city partnerships (ISCPs) has expanded since the postwar era, developing from cultural exchanges into strategic diplomatic channels for sustainable development. While their socioeconomic benefits are well‐documented, their potential as instruments for global environmental governance and urban decarbonization remains underexplored. This study utilizes a panel dataset of 296 Chinese cities spanning the period 2000–2022 to empirically examine the impact of ISCPs on carbon emissions. Using a Bartik shift‐share instrument to address endogeneity, we find that ISCPs causally facilitate decarbonization. Mechanism tests reveal that this effect is primarily realized through green innovation, specifically via substantive technological breakthroughs, with a neutral aggregate impact on incremental green innovation. Notably, this neutrality masks a distinct geopolitical divergence: partnerships with the Global North significantly stimulate both substantive and incremental green innovation, whereas collaborations with the Global South fail to promote substantive technological breakthroughs and may temporarily constrain incremental green innovation. Furthermore, heterogeneity analyses reveal that the decarbonization effect is heavily contingent on high foreign direct investment and advanced economic development, underscoring the critical role of local absorptive capacity. Regional analysis further demonstrates that this impact is highly significant in Western China, highlighting the potential of city diplomacy as an institutional substitute for missing market channels for decarbonization. Based on these empirical findings, policymakers should optimize the structural layout of city diplomacy, prioritize substantive innovation quality over patent quantity, provide targeted subsidies to cross absorptive thresholds, and strategically direct sister city networks toward traditional industrial regions with high carbon footprints.