Historic International Court of Justice Opinion Confirms States’ Climate Obligations

The World’s Eyes Turn to the Hague

On 23 July 2025, the International Court of Justice (ICJ) delivered its landmark advisory opinion on ‘the obligations of states with respect to climate change’ at the Peace Palace in The Hague.

The Court determined that the 1.5°C temperature target is legally binding under the Paris Agreement and that all states, in particular the largest emitters, must take ambitious mitigation measures in line with the best available science. The opinion arrives six years after a group of 27 students from the University of the South Pacific began campaigning on this issue, and more than two years since the United Nations General Assembly (UNGA) adopted a resolution requesting the advisory opinion.

The Court rejected arguments from some high-emitting states that climate treaties are the only applicable law to the climate crisis, excluding broader international law. It found that multiple sources of law impose legal duties on states to prevent “transboundary environmental harm”, act with precaution, and take due diligence measures to reduce greenhouse gas (GHG) emissions and adapt to the adverse impacts of climate change.

The ICJ’s Answers: States must act — or be held responsible

The Court left no doubt that international law provides a sufficiently robust framework to assess climate-related state responsibility, while acknowledging the unique features of climate change.

Key findings include:

• 1.5°C is the primary agreed legally binding target for limiting the global average temperature increase under the Paris Agreement, noting that every increment of global warming escalates climate risks.
• Customary international law imposes binding obligations on states to take preventive and precautionary measures to avoid climate harm, including through the regulation of private actors.
• While emission of GHGs is not per se unlawful, failure to take appropriate measures to prevent foreseeable harm — including through fossil fuel production and consumption, new exploration licenses, subsidies, or inadequate regulation—can constitute a wrongful act attributable to the state.
• States must regulate private actors’ emissions as part of their due diligence obligations. Where states fail to do so, responsibility arises from their failure to regulate the conduct of private actors within their jurisdiction or control.
• Both customary international law and climate treaties, such as the UN Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, impose binding obligations on states to undertake adaptation measures in line with the best available science. And developed countries have the additional responsibility to help developing countries meet the costs of adaptation.
• Scientific evidence allows emissions to be attributed to individual states, including cumulative historical and current emissions. This enables states harmed by climate change to invoke legal responsibility. All states have a legal interest in compliance. As such, any state—not only those harmed directly—can invoke responsibility for breaches of climate obligations under customary international law and climate treaties.

Climate Inaction Can Trigger Legal Consequences

The Court confirmed that states violating their international obligations can face the full range of legal consequences under the law of state responsibility:

• Cessation and guarantees of non-repetition: States must stop wrongful acts, which in some cases may amount to revoking policies or licences that promote fossil fuel activity. They may also be required to provide assurances against future breaches.
• Reparation: Where harm is shown, states must make full reparation. These can include:
• Restitution such as ecosystem restoration or rebuilding climate-resilient infrastructure;
• Compensation for financially quantifiable loss, or;
• Satisfaction including public acknowledgement or apology.

Even where they have breached their obligations, states have a continuing duty to comply — such as by submitting new or revised nationally determined contributions (NDCs) under the Paris Agreement that must be progressively ambitious.

While the Court did not apportion blame or quantify compensation, it clarified that such determinations are legally permissible and must be made on a case-by-case basis based on a “sufficiently direct and certain causal nexus” between the wrongful act and the harm suffered.

Opinion Puts Fossil Fuel Producers on Notice

The opinion has significant implications for energy producers. The Court was clear that the “relevant conduct” for the proceedings was not limited to conduct that itself directly results in GHG emissions (i.e. fossil fuel combustion) but rather comprises “all actions or omissions of States which result in the climate system and other parts of the environment being adversely affected by anthropogenic emissions”. In other words, fossil fuel production is included in the scope of conduct that can potentially be in breach of international law.

In particular, issuing fossil fuel exploration licences, allowing new production projects, or granting fossil fuel subsidies can be a breach of international law. The Court explicitly said that “a state’s failure to take appropriate action to protect the climate system from GHG emissions – including through fossil fuel production, fossil fuel consumption, the granting of fossil fuel exploration licenses or the provision of fossil fuel subsidies — may constitute an internationally wrongful act.”

This means states that produce coal, oil and gas are put on notice. Any expansion of production will now attract increased legal risk.

• Stop issuing new fossil fuel exploration licenses;
• Stop issuing development consents for new fossil fuel extraction projects; and
• Adopt regulations to phase out fossil fuel production.

A Major Shift in How Climate Change Adaptation is Perceived

The Court was equally clear that “adaptation obligations under the Paris Agreement complement the mitigation obligations in preventing and reducing the harmful consequences of climate change.”

Simply put, the level and need for future adaptation depends on states’ mitigation ambition and emission reductions today.

The ICJ’s opinion found that states have legal obligations under the climate treaties, customary international law, and other applicable international law, to carry out climate adaptation planning and implement adaptation actions, in line with the best available science. It spelled out that the adverse effects of climate change may “significantly impair the enjoyment of certain human rights,” including the right to life; to a healthy environment; to health; to an adequate standard of living; to privacy, family and home; and to the rights of women, children and indigenous peoples.

In other words, the ICJ sees states’ failure to implement adequate and timely adaptation measures as a potential violation of their international human rights obligations.

This opinion represents a major shift in how adaptation is perceived under global policy frameworks. While it has often been treated as optional or secondary, this decision puts adaptation on equal legal footing with mitigation efforts to cut emissions.

In addition, the Court also considers adaptation measures as a part of states’ customary duty to prevent significant harm to the environment by acting with due diligence. Applying a due diligence lens to states’ adaptation obligations allows for an assessment of whether governments are making serious, genuine efforts taking timely, informed, and credible adaptation actions in meeting their obligations under applicable treaties and customary international law.

What all this means is that the advisory opinion raises the bar for governments.

Adaptation can no longer be treated as an option, but a legal obligation. It clarifies governments’ accountability for their (in)action on strengthening resilience and providing support for the most vulnerable countries in meeting the costs of adaptation.

It also empowers the most vulnerable and most affected communities to assert their right to demand concrete, timely adaptation planning and meaningful actions and support to cope with the real and growing impacts of climate change now backed by international law.

Related Articles: ICJ to Rule on States’ Climate-related Obligations: How Did We Get Here? | Healthy Environment: A Human Right and Customary International Law | Can ICJ Advisory Opinion on Climate Change Contribute to the SDG Discourse?

Advisory Opinion Underlines Urgency of ISDS Reform

The opinion also carries major implications for international investment law. Fossil fuel investors have increasingly relied on investor-state dispute settlement (ISDS) to challenge climate-related regulations, including phase-outs, licensing bans, or fiscal reforms.

The ICJ’s opinion reinforces that states have a legal duty — not mere policy discretion — to adopt and maintain ambitious climate measures. This should rule out claims from investors alleging that such climate action violates investment law because they are supposedly arbitrary or unfair.

The Court specifically emphasizes that states can be responsible for failing to take necessary “measures to limit the quantity of emissions caused by private actors under its jurisdiction.” This unequivocally includes an obligation to limit emissions caused by foreign investors, including fossil fuel companies, who might use ISDS to challenge such action internationally.

In addition, the opinion directly addresses fossil fuel licensing and subsidy regimes, areas that have previously triggered ISDS claims and are likely to lead to further disputes. The Court’s reasoning implies that states may have a duty to revise or rescind such licensing and subsidy policies, even if these changes lead to investor-state claims.

Moving forward, international investment law must not be designed or interpreted in a way that impedes or penalizes states for fulfilling their international obligations on climate change — investment treaties and other instruments that are not aligned with this interpretation must be reformed.

The Court affirmed that states’ climate obligations are owed to the entire international community. Consequently, foreign investors cannot credibly assert — as they often do in ISDS claims — that they legitimately expected a host state to continue violating these universal obligations, such as by issuing or extending fossil fuel exploration or production licenses.

Judge Sarah Cleveland underscored these implications in her separate declaration. Citing the IPCC’s recognition that ISDS can deter climate regulation (so-called “regulatory chill”), she clarified that investment treaties must not be interpreted in isolation, but in harmony with international climate law.

The ICJ opinion and Cleveland’s declaration strengthen the case for reforming investment treaties to bring them in line with climate commitments. In particular, states should consider steps such as:
•    Carving out lawful climate measures from compensation claims;
•    Limiting forward-looking damages that penalize states for avoided emissions;
•    Reforming or removing ISDS mechanisms that deter regulatory action.

Ultimately, the ICJ affirmed that international law supports — not hinders — climate ambition. The obligation to act cannot be overridden by investment protections for private investors that run counter to the international legal interest in preserving a stable climate system.

A Global Legal Foundation for Climate Action

The ICJ’s advisory opinion follows similar climate-related conclusions on states’ obligations to address climate change. In 2024, the European Court of Human Rights recognized that insufficient climate action can constitute a violation of human rights, following a claim by a group of over 2000 senior Swiss women against the Swiss state. Opinions from the International Tribunal for the Law of the Sea, which looked at the obligations under the UN Convention on the Law of the Sea, and the Inter-American Court on Human Rights, as analyzed by IISD, have also come to similar conclusions. The African Court on Human and People’s Rights has also been requested to give an advisory opinion.

The ICJ opinion affirms what many legal scholars and advocates have long argued: states have binding obligations to prevent climate harm and can be held responsible for failing to do so. The ICJ has now authoritatively interpreted international law in a way that strengthens the legal foundation for ambitious, science-based climate action.

The opinion is likely to influence future domestic and international climate litigation, shape negotiations under the UN climate regime, and provide new leverage to vulnerable states seeking accountability and climate justice.

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This article was originally published by the International Institute for Sustainable Development (IISD) and is republished here as part of an editorial collaboration with the IISD. It was authored by Lukas Schaugg, Natalie Jones, and Jeffrey Qi. The authors would like to thank Nathalie Bernasconi-Osterwalder, Anne Hammill and Farooq Ullah for their guidance and contributions to this article. 

Editor’s Note: The opinions expressed here by the authors are their own, not those of Impakter.com — In the Cover Photo: Obligations of States in respect of Climate Change – Reading of the Advisory Opinion of the Court,  July 23, 2025. Cover Photo Credit: International Court of Justice.