On July 23, 2025, the International Court of Justice delivered its Advisory Opinion on the Obligations of States in respect of Climate Change, unanimously establishing that states have comprehensive binding obligations under multiple frameworks of international law to protect the climate system. The Court’s opinion responded to questions posed by the UN General Assembly through resolution 77/276, marking only the fifth unanimous advisory opinion in the Court’s nearly 80-year history.

In its Advisory Opinion, the Court identified specific obligations under various climate treaties, including that states parties to the Paris Agreement must “act with due diligence in taking measures in accordance with their common but differentiated responsibilities and respective capabilities capable of making an adequate contribution to achieving the temperature goal”. The Court further held that states must “prepare, communicate and maintain successive and progressive nationally determined contributions” that collectively can achieve this temperature goal, and that they have obligations of adaptation and cooperation, including through technology and financial transfers, which must be performed in good faith.

Significantly, the Court held that customary international law imposes a duty on states “to use all means at their disposal to prevent activities carried out within their jurisdiction or control from causing significant harm to the climate system.” The Court characterized these obligations as erga omnes, meaning “all States have a common interest in the protection of global environmental commons like the atmosphere and the high seas,” allowing any state to invoke responsibility for breaches.

Addressing state responsibility, the Court found that “it is scientifically possible to determine each State’s total contribution to global emissions, taking into account both historical and current emissions.” The Court clarified that “the internationally wrongful act in question is not the emission of greenhouse gases per se, but the breach of conventional and customary obligations,” including failures in regulating private actors. States may be held responsible for “fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licences or the provision of fossil fuel subsidies.” On causation, the Court acknowledged that while “the causal link between the wrongful actions or omissions of a State and the harm arising from climate change is more tenuous than in the case of local sources of pollution,” this does not make establishing causation impossible. The Court endorsed a flexible standard requiring “a sufficiently direct and certain causal nexus” determined through case-by-case assessment, with scientific evidence establishing that “significant harm to the climate system has been caused as a result of anthropogenic greenhouse gas emissions.”

The proceedings drew unprecedented participation with 91 written statements, 62 written comments, and oral statements from 96 states and 11 international organizations. The Court concluded by expressing hope that “its conclusions will allow the law to inform and guide social and political action to address the ongoing climate crisis,” providing guidance that may significantly influence both state conduct and climate litigation worldwide.