ICJ Advisory Opinion on Climate Change (25 July 2025)[1]
The ICJ’s Advisory Opinion on climate change, delivered on 25 July 2025, marks a pivotal moment in international law. It was adopted by consensus after a historic campaign led by youth from Vanuatu, which prompted the General Assembly, through resolution 77/276, to request the Court’s guidance on the obligations governing states’ conduct on climate change and the legal consequences of breaches of those obligations.
As a law student, it is especially inspiring that this initiative began with students from Vanuatu. The Court itself acknowledged the importance of youth in addressing climate change, expressly referring to the rights of future generations (paras 155-157) and thereby underscoring the long-term consequences of present decisions and the value of integrating youth perspectives into climate governance.
Another feature I found particularly important is the Court’s heavy reliance on scientific consensus, as it affirms the reality of the problem and provides the law with a solid factual foundation. The Court drew extensively on the findings of the Intergovernmental Panel on Climate Change (IPCC) and other authoritative scientific sources, often using their language directly rather than substituting its own formulations. In doing so, it used science as the interpretive background for existing legal obligations. This approach also led the Court to treat the Paris Agreement not as a merely aspirational instrument but as one that creates binding obligations (para. 224), significantly narrowing the discretion afforded to states in formulating their nationally determined contributions.
Against this background, the panelists explored the ICJ’s analysis on climate change law and international environmental law, the Court’s decision on state responsibility, as well as the effects of the decision for human rights, investment arbitration, and corporate and financial regulation. The panellists also identified some omissions.
The Advisory Opinion and International Environmental Law
The Court placed climate change law within the broader framework of international environmental law, making clear that it is not an isolated regime. It drew upon principles from the Rio Declaration (para 140) and integrated other environmental treaties—such as the Convention on Biological Diversity (paras 325-330) and the Convention to Combat Desertification (paras 331-334)—into its reasoning. Dr Duvic-Paoli emphasised that this holistic approach counteracts the risk of treating international law in silos.In the same vein, the Court confirmed the applicability of general international law in the context of climate law. The Court made clear that international climate law is not a self-contained regime: general rules, including the law of state responsibility, apply fully. Although the UN Charter does not mention the environment, the Court found that obligations under the Charter relating to cooperation and the protection of human rights cannot be fulfilled without taking environmental considerations into account (para 115). It also aligned its approach with the International Tribunal for the Law of the Sea[2] by recognising a stringent standard of due diligence.
Importantly, the Court affirmed that “States have a duty under customary international law to prevent significant harm to the environment”( para 132), and that this duty arises as a result of the general risk of significant harm to which States contribute (para 133); it clarified that this obligation extends to the climate system and is central to legal relations among States.
State Responsibility
To begin with, on the issue of lex specialis, the Court concluded that a breach of climate obligations constitutes an internationally wrongful act that gives rise to state responsibility. Following the line advanced by Vanuatu and other developing countries, the Court found there was no discernible intention to displace general rules of state responsibility and that the treaties’ mechanisms are cooperative and facilitative, not designed to address liability or compensation. Consequently, the Court held that the climate treaties were not lex specialis and that general international law, including the rules on secondary obligations, is applicable (paras 162-171).
Turning to attribution, the Court acknowledged the difficulty that climate harm results from the cumulative effect of countless public and private actions. It clarified that greenhouse gas emissions are not themselves wrongful acts, but breaches of the duty to prevent significant harm can be attributed to a state when they arise from its own conduct or from its failure to regulate private actors under its jurisdiction, for example through subsidies or licensing (paras 425-432). Dr Ridi observed that the Court’s language suggested something closer to the articulation of new primary obligations rather than the straightforward application of attribution rules. The Court explained that existing flexible legal standards are sufficient to address causation. It further clarified that the existence of concurrent causes does not absolve a state of responsibility, and that responsibility may still be invoked against a single state even when multiple states contributed (paras 433-438).
Human Rights
The Court expressly linked climate issues to human rights, focusing on existing rights—including the rights to life (para 377), privacy, family and home (para 381), health, and water (para 292)—and stressing states’ duties towards vulnerable groups such as women, children, persons with disabilities, and migrants (paras 382-384). Notably, it also affirmed that the principle of non-refoulement applies to climate-related migration (para 378).
Furthermore, the Court for the first time recognised a right to a clean, healthy, and sustainable environment (paras. 387–393) and made important observations regarding sea level rise, maritime spaces, and continued statehood (paras. 355–365). For this, the Court relied on regional human rights instruments that already recognise this right: Article 24 of the African Charter on Human and Peoples’ Rights guarantees “a general satisfactory environment favourable to [peoples’] development”; Article 38 of the Arab Charter on Human Rights affirms a “right to a safe environment” as part of the right to an adequate standard of living; and Article 11 of the Additional Protocol to the American Convention on Human Rights (Protocol of San Salvador) states that “[e]veryone shall have the right to live in a healthy environment.” As Ms Willman mentioned, it is our very own European Convention on Human Rights which lacks any such provision, which the Court’s Opinion should serve as a call to include an express right to a healthy environment in.
Investment arbitration
Dr López stressed the interpretative implications of the Court regarding the principle of lex specialis, noting that states will need to consider the Court’s approach when framing arguments before investment treaty tribunals. In her view, the Court’s emphasis on systemic integration could serve as guidance to such tribunals, which have often adopted a restrictive approach to Article 31(3)(c) of the Vienna Convention on the Law of Treaties.
Dr López emphasised that the Court’s identification of the customary duty to prevent significant harm—including obligations to adopt rules and measures and to conduct environmental impact assessments—means that states not only have a right to regulate but also a duty to do so, which investment tribunals will therefore have to take into account. The Advisory Opinion has important implications for the oil and gas industry: states are obliged to control private actors within their jurisdiction, and a failure to act may constitute an internationally wrongful act. This extends to decisions on granting or refusing licences for fossil fuel exploration or production. Such reasoning affects how tribunals interpret the principles of fair and equitable treatment and legitimate expectations, as extractive companies can no longer assume that concessions will always be granted.
Professor Ortino examined the broader structural implications for investment treaties. The Court’s articulation of a stringent duty of due diligence, requiring states to use all means available to prevent significant harm, pressures states to reassess their treaties. While investment treaties do not directly generate emissions, they may indirectly do so by creating “regulatory chill” that deters states from adopting mitigation measures such as phasing out fossil fuels—a phenomenon recognised by the IPCC.
Professor Ortino argued that states should modify existing treaties and design future ones to avoid undermining their climate obligations. Possible options include excluding protections for fossil fuel investments, limiting pre-establishment commitments in critical sectors, and incorporating provisions supporting mitigation policies, transparency, and responsible business conduct. He warned that investment protection cannot be reduced to proportionality or cost–benefit balancing, as this would allow tribunals to weigh foreign investment interests against climate policies in ways inconsistent with the Court’s reasoning.
Corporate and Financial Regulation
The Court expressly included within the scope of state responsibility not only state actors but also non-state actors under a state’s jurisdiction or effective control (para 95). This opens avenues for corporate litigation at the national level, building on precedents such as the Dutch Shell case.[3]
Professor Bowman added that the Advisory Opinion strengthens the case for states to adopt robust regulatory measures. Beyond informational tools such as reporting and disclosure, these may include mandatory transition plans, amendments to directors’ duties, heightened capital and supervisory requirements for financial institutions, and command-and-control measures. Such steps reflect that incremental adjustments will no longer suffice to implement the Court’s reasoning.
Points the Court Could Have Addressed More Clearly
Dr Duvic-Paoli identified important omissions. Despite relying on the Rio Declaration, the Court gave little attention to international law on sustainable development. It also avoided addressing the economic realities of differentiation—such as the principle of common but differentiated responsibilities—or the developmental priorities of emerging economies. Moreover, although the Court mentioned future generations and public participation, these were not integrated into its core reasoning.
Ms Willman noted that from a human rights perspective, the Court—like ITLOS, the ECtHR, and the IACtHR before it—failed to adopt an ecocentric perspective that could have recognised rights of nature itself, as done in certain indigenous legal systems, which might have provided a stronger basis for environmental protection.
Dr Ridi also highlighted unclear points. The Court characterised the relevant obligations as erga omnes (paras 439-443), but as Judge Tladi noted, the consequences of this characterisation remain uncertain, especially given tensions in the Court’s jurisprudence—such as the 2024 Palestine Advisory Opinion—[4]which conflated erga omnes obligations with jus cogens norms.[5] The Court also treated all states equally, without distinguishing between major emitters and specially affected states, which could have significant implications in future disputes. Furthermore, it did not address the consequences of conduct that was lawful when undertaken but nonetheless harmful, despite existing legal doctrines that could have provided avenues for redress.
Finally, arbitration was only briefly mentioned in a separate opinion by Judge Cleveland, even though—as the panel noted—the implications could be significant. This was a missed opportunity for the Court to engage more fully with a key area where its reasoning will have considerable impact.
Conclusion
This Advisory Opinion is a landmark step in clarifying the international legal obligations relating to climate change—an issue that, in the Court’s own words, poses an “urgent and existential threat” (para 73) and which we must begin addressing now, as the Court itself paves the way for. However, the effective realisation of the rights and duties it affirms will depend on how, as Ms Willman mentioned, practitioners and academics (and we, future practitioners and defenders of human rights and the environment) develop its potential uses and ensure its dissemination.
[1] Advisory Opinion on the Obligations of States in respect of Climate Change (23 July 2025) ICJ (General List No 187).
[2] Request for Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (21 May 2024) ITLOS Reports 2024 (Case No 31)
[3] Milieudefensie and Others v Royal Dutch Shell plc (The Hague District Court, Judgment of 26 May 2021).
[4] Legal Consequences Arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem (Request for Advisory Opinion, 19 July 2024) ICJ.
[5] Declaration of Judge Dire Tladi, appended to the Advisory Opinion on the Obligations of States in respect of Climate Change (23 July 2025) ICJ AO, paras 35-57.