Obligations of States in Respect of Climate Change (ICJ Advisory Opinion)

The advisory opinion on the Obligations of States in Respect of Climate Change originated in a campaign led by Pacific island states, principally Vanuatu, working with a coalition of small island developing states and a student movement that began at the University of the South Pacific. On 29 March 2023 the United Nations General Assembly adopted by consensus Resolution 77/276, requesting the International Court of Justice to render an advisory opinion under Article 65 of the ICJ Statute and Article 96 of the UN Charter. The resolution posed two questions: first, what obligations international law imposes on states to ensure protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions for present and future generations; and second, what the legal consequences are for states that, by their acts and omissions, have caused significant harm to the climate system, with particular regard to small island developing states and to peoples and individuals affected. The Court delivered its opinion on 23 July 2025.

Procedurally, the request engaged the Court's advisory jurisdiction, which is consultative rather than contentious and binds no party as res judicata. After Resolution 77/276 was transmitted, the Court fixed deadlines for written statements and written comments, drawing an unprecedented volume of participation. More than ninety states and a dozen international organisations submitted written statements, and the oral hearings held at the Peace Palace in The Hague in December 2024 constituted the largest set of proceedings in the Court's history by number of participants. The Court then deliberated and issued a single unanimous opinion, supplemented by individual declarations and separate opinions from judges elaborating points of emphasis on intergenerational equity, the precautionary approach, and the scope of reparation.

In substance the Court drew the applicable law from multiple, mutually reinforcing sources rather than treating the climate treaty regime as exclusive. It identified obligations arising under the UN Framework Convention on Climate Change (1992), the Kyoto Protocol, and the Paris Agreement (2015) — including the duty to prepare, communicate, and pursue measures to achieve nationally determined contributions under Paris Article 4. Crucially, it held that obligations also flow from customary international law, notably the duty to prevent significant transboundary environmental harm and the duty of due diligence, as well as from the UN Convention on the Law of the Sea, human rights treaties, and the principle of cooperation. The Court characterised the prevention of climate harm as an obligation of conduct requiring stringent due diligence calibrated to a state's capabilities and to the best available science, and treated certain core climate obligations as erga omnes — owed to the international community as a whole.

The opinion lands within an identifiable wave of international climate adjudication. It followed the International Tribunal for the Law of the Sea advisory opinion of 21 May 2024, which held that greenhouse gas emissions constitute marine pollution under UNCLOS, and the Inter-American Court of Human Rights advisory opinion requested by Chile and Colombia and issued in 2025. The European Court of Human Rights had already, in Verein KlimaSeniorinnen Schweiz v. Switzerland (9 April 2024), found a violation of the Convention arising from inadequate Swiss climate policy. Capitals from Port Vila to Berlin, ministries of foreign affairs, and climate negotiators preparing for successive Conferences of the Parties have treated the ICJ pronouncement as the authoritative synthesis of these strands.

The advisory opinion is distinct from a contentious judgment of the Court: it neither resolves a dispute between named parties nor produces an enforceable order, and it differs from a binding arbitral award such as those rendered under UNCLOS Annex VII. It should not be conflated with the Paris Agreement's own compliance mechanism under Article 15, which is facilitative and non-adversarial. Nor is it identical to the ITLOS opinion, which was confined to the law of the sea; the ICJ opinion is broader, integrating treaty law, custom, and human rights into a unified statement of obligation. Its authority rests on the Court's standing as the principal judicial organ of the United Nations rather than on formal bindingness.

Controversy attended the proceedings before and after delivery. Major emitting states, including the United States and several others, argued in their submissions that the climate treaty regime — the UNFCCC and Paris Agreement — constituted lex specialis that should largely displace general international law obligations, an argument the Court declined to accept in its expansive form. Debate persists over the practical content of reparation: the Court acknowledged that legal consequences for breach include cessation, guarantees of non-repetition, and reparation, while recognising the evidentiary difficulty of attributing specific damage to specific states. Questions of causation, the temporal reach of obligations toward future generations, and the relationship between collective and individual state responsibility remain contested terrain for subsequent litigation.

For the working practitioner the opinion is a reference instrument of immediate utility. Litigators in domestic and regional courts cite it to establish the content of due diligence and the existence of erga omnes climate duties; treaty negotiators invoke it to resist arguments that Paris commitments are merely aspirational; and legal advisers in foreign ministries use it to calibrate state positions on loss and damage, finance, and the ambition of nationally determined contributions. Although non-binding, the opinion carries substantial persuasive weight and is likely to shape the interpretation of climate obligations across forums for the foreseeable future.