Authored By: Urooj Fatima
Bahria University Islamabad
I. Introduction
For more than a decade, states facing climate liability claims could fall back on one dependable line of defence: international law, so the argument went, never actually specified what a state owed the climate system, or what was supposed to happen when a state fell short. That defence stopped working on 23 July 2025. Sitting as a full bench, the International Court of Justice issued its first advisory opinion on climate change and did so unanimously, concluding that states carry binding obligations to protect the climate system and can incur international responsibility reparations included when they do not.[1]
The case did not arrive through the Court’s usual contentious channel. The UN General Assembly requested the opinion at Vanuatu’s urging, and Vanuatu’s involvement traces back further still, to a group of Pacific law students who wanted to know why a body of doctrine as developed as state responsibility had never been trained directly on the greatest harm of this century. What follows is an argument that the Court’s answer pulls climate governance out of the register of voluntary diplomatic pledging and into the ordinary law of state responsibility even as it leaves the practical mechanics of enforcement noticeably less settled than the doctrine it just announced. The article works through the legal framework the Court relied on, reads the opinion against two related rulings from other tribunals, weighs its strengths against its limits, and closes by looking at how states have actually reacted.
II. The Legal Framework: Treaty, Custom, and Human Rights Law
Any assessment of state climate obligations has to start with the treaty structure built on the UN Framework Convention on Climate Change and the Paris Agreement, under which parties commit to pursuing efforts to limit warming and to filing Nationally Determined Contributions that grow more ambitious over time.[2] The threshold question for the Court was whether this treaty regime is self-contained whether it displaces every other body of international law that might otherwise bear on state conduct. A number of respondent states, mostly major historical emitters, pushed hard for that reading, arguing that the Paris Agreement was a carefully negotiated, deliberately procedural compromise that should not be topped up with tougher obligations imported from elsewhere.
The Court did not accept that argument. Climate treaties, customary international law, and human rights law, it held, all operate at once, each shaping the meaning of the others rather than one simply crowding out the rest.[3] Custom supplied the long-standing duty to prevent significant transboundary environmental harm and the duty of good-faith cooperation between states. Human rights law supplied something arguably more far-reaching: the idea that a stable climate is a precondition for enjoying basic rights at all, which means a state’s human rights obligations reach the climate system itself.[4] Put together, this reasoning shuts down the argument that compliance with the Paris Agreement, on its own, exhausts what a state owes on climate.
III. The Advisory Opinion and Its Companion Rulings
The ICJ opinion is not a standalone event. It is the third of three advisory rulings handed down by international tribunals within roughly a year, and it reads differently once set alongside the other two.[5] In May 2024, the International Tribunal for the Law of the Sea found that greenhouse gas emissions count as marine pollution under the UN Convention on the Law of the Sea, meaning states owe specific obligations to cut emissions under that Convention quite apart from anything they owe under the climate treaties.[6] Then, days ahead of the ICJ’s own ruling in July 2025, the Inter-American Court of Human Rights went a step further and described certain environmental protections as peremptory norms of international law a status the ICJ, notably, did not adopt for itself.[7] Within the opinion itself, the most consequential finding concerns what due diligence actually requires. Leaning on the scientific findings of the Intergovernmental Panel on Climate Change as the best available account of climate causes and consequences, the Court held that a state’s Nationally Determined Contribution must reflect that state’s highest possible ambition and show progression from one submission to the next.[8] It also held that a state’s due diligence duties are not limited to its own conduct: they extend to regulating private actors within its jurisdiction, so that continued fossil fuel licensing, or simply keeping fossil fuel subsidies in place, can itself amount to a breach.[9] On what follows from a breach, the Court applied the ordinary secondary rules of state responsibility a wrongful failure to protect the climate system triggers cessation, assurances of non-repetition, and full reparation through restitution, compensation, and satisfaction, so long as a sufficiently direct and certain causal link between breach and injury can be shown.[10]
IV. An Advisory Victory with Practical Limits
The opinion’s real achievement is doctrinal: it converts a body of soft diplomatic expectation into hard secondary rules of responsibility. Once a failure to regulate emissions can qualify as an internationally wrongful act, the full machinery of state responsibility attribution, cessation, reparation becomes available to injured states in a way that mere non-compliance with a voluntary pledge never allowed. That the full fifteen-judge bench reached this conclusion unanimously matters too; it closes off the claim, still heard in domestic climate litigation only a few years back, that the underlying international legal position is genuinely up for debate.
That achievement still has real limits, and three are worth dwelling on. An advisory opinion, first, carries no binding force of its own it persuades rather than compels, and how much it actually changes depends on whether domestic courts, treaty bodies, and contentious tribunals pick it up.[11] Second, the causation standard the Court set, though more forgiving than some respondent states wanted, still demands proof of a sufficiently direct and certain link between one state’s conduct and one specific injury a bar that stays genuinely hard to clear given how cumulative and diffuse greenhouse gas emissions are across many states and long stretches of time.[12] Third, and following from the second point, the opinion sets out the legal test for a wrongful act without naming any state as having committed one; that finding is reserved for contentious proceedings the opinion cannot itself produce.
The opposing argument deserves a fair hearing here. Respondent states maintained throughout the proceedings that treating ordinary regulatory choices energy policy, industrial licensing as potential grounds for international liability risks turning fundamentally political and economic judgments into questions of legal exposure, with knock-on effects for sovereign policy space that the climate treaties were drafted precisely to avoid. The Court’s response, that due diligence is judged against a state’s own capabilities and circumstances rather than a single uniform standard, softens this worry without erasing it. Where legitimate regulatory discretion ends and internationally wrongful inaction begins will probably only get worked out through a run of future contentious cases applying the opinion’s reasoning.
V. Comparative State and Institutional Responses
States reacted to the opinion in largely predictable ways. Germany’s environment ministry treated the confirmation of universal mitigation obligations as consistent with a responsibility it had already accepted, while a spokesperson for the US administration declined to engage with the substance of the opinion at all, framing government priorities around domestic interests rather than international legal obligation.[13] China described the opinion as consistent with positions developing states had long advanced, while pointing to its own record on emissions reduction and green technology rather than accepting any suggestion of individual responsibility for historical emissions.
These divergent reactions point to a comparative question that will shape how the opinion actually gets absorbed into domestic legal systems. In monist jurisdictions, where international law applies directly, and in states whose constitutional courts have already shown a willingness to read domestic environmental duties in light of international standards, the opinion gives an immediately usable benchmark against which national climate policy and Nationally Determined Contributions can be measured. In more dualist systems, where international law needs domestic incorporation before courts can enforce it directly, the opinion’s influence is more likely to be indirect persuasive authority that shapes statutory interpretation and policy debate rather than a directly enforceable standard. Climate-vulnerable states occupy a third position altogether: for them, the opinion works less as a domestic compliance benchmark and more as leverage in ongoing negotiations over loss and damage finance, where framing climate harm as a matter of state responsibility, rather than voluntary solidarity, meaningfully strengthens their hand at the table.
VI. Conclusion
This article has argued that the International Court of Justice’s 2025 advisory opinion marks a genuine doctrinal shift in international climate governance moving the field away from voluntary treaty commitment and toward the ordinary law of state responsibility, while leaving substantial evidentiary and enforcement questions open. The Court’s findings on due diligence, wrongful acts, and reparation give, for the first time, an authoritative and unanimous statement of what international law asks of states on greenhouse gas emissions, and what happens when they fall short.
A few consequences follow. Domestic courts and legislatures should treat the opinion’s due diligence standard as an interpretive benchmark when judging whether national climate policy is adequate. Climate-vulnerable states and their counsel should put resources into the attribution science needed to meet the Court’s causation threshold before bringing contentious claims, rather than treating the advisory opinion as self-executing proof of liability. And negotiators working the loss and damage process, more broadly, should treat the opinion as a legal floor under current diplomatic bargaining not a ceiling on what climate justice ultimately demands. The Pacific law students whose initiative set all of this in motion wanted a clear statement of the law. The Court has now given them one. What is left is the considerably harder task of turning that statement into an actual remedy.
Reference(S):
Cases
Obligations of States in respect of Climate Change (Advisory Opinion) [2025] ICJ Rep, 23 July 2025
Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Case No 31, International Tribunal for the Law of the Sea, Advisory Opinion, 21 May 2024
The Climate Emergency and Human Rights, Advisory Opinion OC-32/25, Inter-American Court of Human Rights, 3 July 2025
Legislation
Paris Agreement to the United Nations Framework Convention on Climate Change (adopted 12 December 2015, entered into force 4 November 2016) T.I.A.S. No. 16-1104
United Nations Convention on the Law of the Sea (adopted 10 December 1982, entered into force 16 November 1994) 1833 UNTS 3
United Nations Framework Convention on Climate Change (adopted 9 May 1992, entered into force 21 March 1994) 1771 UNTS 107
UNGA Res 77/276 (29 March 2023) UN Doc A/RES/77/276
[1]Obligations of States in respect of Climate Change (Advisory Opinion) [2025] ICJ Rep, 23 July 2025.
[2]Paris Agreement to the United Nations Framework Convention on Climate Change (adopted 12 December 2015, entered into force 4 November 2016) T.I.A.S. No. 16-1104, art 4.
[3]Obligations of States in respect of Climate Change (n 1) paras 161-172.
[4]ibid para 373; para 457(3)(E).
[5]House of Commons Library, ‘Climate Change at the International Court of Justice’ (UK Parliament, 2026).
[6]Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law, Case No 31, International Tribunal for the Law of the Sea, Advisory Opinion, 21 May 2024.
[7]The Climate Emergency and Human Rights, Advisory Opinion OC-32/25, Inter-American Court of Human Rights, 3 July 2025.
[8]Obligations of States in respect of Climate Change (n 1) para 74, paras 240-242.
[9]ibid paras 245, 427.
[10]ibid paras 427, 436, 438.
[11]Statute of the International Court of Justice (adopted 26 June 1945, entered into force 24 October 1945) 33 UNTS 993, art 65; Miriam Cohen, ‘A Panoply of Consequences?: Remedies and Reparations in the ICJ’s Climate Opinion’ (Verfassungsblog, 2026).
[12]‘The 2025 International Court of Justice Advisory Opinion on Obligations of States in respect of Climate Change’ (2025) International and Comparative Law Quarterly.
[13]House of Commons Library (n 5).
