Abstract This analysis of the Advisory Opinion of the International Court of Justice (ICJ) on climate change focuses on the application of customary international law. The ICJ identifies a customary duty to prevent significant harm to the climate system and some more specific obligations. It notes that these rules apply to every State, irrespective of their participation in climate treaties. What remains less clear, however, is the content of the duty of prevention and, more pragmatically, how courts could assess compliance with this duty. This analysis interprets the Advisory Opinion as suggesting that courts could rely on a set of indicia to determine whether, as a whole, a State is making efforts consistent with customary international law.
Benoit Mayer (2026) studied this question.