In July 2025, the International Court of Justice (ICJ) issued its first-ever advisory opinion on countries’ obligations to address climate change under international law. The ICJ concluded that states’ climate duties arise not only from treaties like the Paris Agreement but also from broader human rights and customary international law obligations — and that failure to act could expose countries to legal risk.
This analysis by Sam Bookman, postdoctoral fellow at the Project on the Foundations of Private Law and lecturer on law at Harvard Law School, provides an overview of the case, summarizes the ICJ’s opinion, and examines its potential implications for the United States, particularly as the U.S. considers rolling back its domestic climate regulations. The ICJ’s opinion may shape future climate litigation around the world and signals that international law is converging on stronger expectations for countries’ actions on climate change.