Does multilateral environmental diplomacy improve environmental quality? The case of the United States

International environmental agreements have multiplied over the last five decades. We examine the impact of multilateral environmental diplomacy on carbon dioxide (CO₂) emissions in the presence of capital formation, renewable energy consumption, and economic growth using the framework of the Environment Kuznets Curve (EKC) and data from the United States from 1980 to 2015. We developed a comprehensive empirical analysis using Zivot–Andrews structural break unit root tests. Co-integration analysis indicates long-run relationships of the variables. The results of the generalized linear models (GLMs) and robust least secure (ROBUSTLS) approach reveal that environmental diplomacy, capital formation, and economic growth deteriorate environmental quality in the long run, while renewable energy consumption improves it. These results support the EKC hypothesis for the United States and suggest that, in the early stages, increased environmental diplomacy stimulates CO₂ emissions to a point, after which CO₂ emissions start declining with further increases in international commitments and strong diplomatic relationships among countries. Policy implications for the United States are presented.