Legal Analysis of the ICJ Advisory Opinion on Climate Change Obligations

The International Court of Justice (ICJ) has delivered an historic advisory opinion which, for the first time, authoritatively sets out States’ legal duties in relation to climate change. It situates the opinion against the backdrop of five decades of treaty‑making and steadily worsening scientific findings on climate change. The Court confirms that climate change is “a quintessentially universal risk” and holds that every State is bound—by treaty and by customary international law—to act with stringent due diligence to prevent significant harm to the climate system and to cooperate internationally to that end. By explicitly recognising the acute vulnerability of small island developing States, the Court validates the core concerns that drove Vanuatu’s campaign for the opinion. 

Key legal duties clarified

The Court characterises anthropogenic greenhouse‑gas emissions as conduct capable of engaging both treaty and customary obligations. It restates the prevention principle and the duty to co‑operate as rules of customary law and emphasises that compliance must be assessed through the prism of the principle of common but differentiated responsibilities and respective capabilities (CBDR‑RC). The latter is described as an “interpretive lens” for all sources, not merely for the climate treaties. For prevention, the Court sets a “stringent” due diligence standard that obliges States to adopt “all appropriate measures”, including rapid, deep and sustained domestic mitigation, supported by legislation, enforcement and continuous scientific review. The duty to cooperate is likewise framed as a continuing, good‑faith obligation that requires collective elaboration and periodic strengthening of rules, standards and scientific programmes.

The opinion integrates international human rights law, identifying the rights to life, health, an adequate standard of living, and the right to a clean, healthy and sustainable environment as directly threatened by climate change; it affirms that environmental protection is a pre‑condition for their enjoyment. The Court also affirms the International Tribunal on the Law of the Sea (ITLOS)’s recent finding that anthropogenic greenhouse gas emissions constitute “pollution of the marine environment” under UNCLOS, thereby triggering Part XII obligations—also to be fulfilled with a stringent due‑diligence standard.

Legal consequences for breaches

Where a State’s acts or omissions cause significant climate harm it incurs the full range of consequences prescribed by the law of State responsibility. These include: (a) a duty of performance (to comply with primary obligations); (b) cessation and guarantees of non‑repetition; and (c) an obligation to make full reparation, which may take the form of restitution, compensation or satisfaction. The Court emphasises that each injured State may invoke responsibility against every wrongful emitter and that obligations toward a stable climate are erga omnes: all States have a legal interest in their observance. 

Implications for Vanuatu and the Pacific

The opinion is a decisive legal vindication of Vanuatu’s leadership. It equips the Government with an authoritative statement that legally binding climate duties have existed for decades, despite historical polluters’ disregard for such duties; that the Paris “loss and damage” finance agenda rests on these hard legal duties, including the duty to make reparations for injury resulting from wrongful acts; and that the continued expansion of fossil‑fuel production is incompatible with States’ obligations of prevention and cessation. Vanuatu may rely on the opinion to press for ambitious NDC revisions at COP 30, to galvanise donor support for the Loss and Damage Fund, and to strengthen its position in any future negotiations on climate justice matters. The finding that responsibility is engaged for cumulative emissions also paves the way for potential litigation against States and possibly corporate actors who have, through their acts and omissions, caused climate harm. 

Next steps

Vanuatu has already started work to integrate the opinion into its climate‑diplomacy toolbox. Immediate next steps include: (1) tabling a resolution in New York that welcomes the opinion and actions its findings; (2) urging developed partners to align bilateral and multilateral climate finance flows with the Court’s guidance; (3) using the opinion to underpin stronger regional positions; and (4) technical work to map the full spectrum of legal implications. In parallel, domestic implementation will demonstrate Vanuatu’s continued good faith commitment to the very obligations it asked the Court to clarify. 

Conclusion

The political language of climate ambition can no longer be detached from enforceable legal duties. For Vanuatu, the opinion is both shield and sword: a shield affirming its right to survival and a sword compelling the world’s major emitters to act in line with science and justice. Disseminating this message widely will reinforce global momentum towards the rapid, just and equitable transition the Court deems a matter of legal obligation.