In a landmark advisory opinion published on July 23, 2025, The International Court of Justice (ICJ) was requested by the United Nations General Assembly (UNGA) , through resolution 77/276, to give its opinion on two key issues[i]:
a. Obligations of States: What are the obligations of States under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases (GHG’s) for States and for present and future generations?
b. Legal Consequences: What legal consequences arise for States that, by acts or omissions, cause significant harm to the climate system and other parts of the environment, with respect to both States (especially those particularly vulnerable to climate change) and peoples/individuals of present and future generations?
Key Findings:
1. Jurisdiction and Admissibility
The Court affirmed it has jurisdiction to issue the advisory opinion as requested. There was no compelling reason to decline the request.
2. Applicable Law
The Court determined that the following sources are the most directly relevant applicable law:
- Charter of the United Nations
- Climate Change Treaties: UN Framework Convention on Climate Change (UNFCCC), Kyoto Protocol, Paris Agreement
- Law of the Sea: United Nations Convention on the Law of the Sea (UNCLOS)
- Other Environmental Treaties: Vienna Convention for the Protection of the Ozone Layer, Montreal Protocol, Convention on Biological Diversity, and UN Convention to Combat Desertification
- Customary International Law: Duty to prevent significant harm to the environment (due diligence) and duty to co-operate
- International Human Rights Law: Core human rights treaties, including the International Covenant on Civil and Political Rights and International Covenant on Economic, Social and Cultural Rights, as well as customary law rights (such as the right to a clean, healthy, and sustainable environment)
- Guiding Principles: Sustainable development, common but differentiated responsibilities and respective capabilities, equity, intergenerational equity, and the precautionary approach/principle.
3. Obligations of States
I. Under Climate Change Treaties
UNFCCC: States must adopt measures contributing to mitigation and adaptation; developed country Parties have additional obligations to lead on limiting GHG emissions and enhancing sinks; all Parties have a duty to co-operate.
Kyoto Protocol: Parties listed in Annex B must comply with emission reduction targets as agreed.
Paris Agreement: States must act with due diligence and in accordance with their common but differentiated responsibilities and capabilities.
Obligations include preparing, communicating, maintaining, and progressively enhancing nationally determined contributions (NDCs) to mitigate climate change, aiming collectively to limit global warming to 1.5°C above pre-industrial levels. Parties must also pursue substantive domestic mitigation measures capable of achieving their NDCs’ objectives, adapt to climate change impacts, and cooperate in good faith—including technology and financial transfers.
II. Under Customary International Law:
States have a duty to prevent significant harm to the environment by acting with due diligence, including regulating activity within their jurisdiction or control, in line with their capacity and responsibilities. They must also co-operate in good faith to prevent harm, requiring sustained and continuous inter-State cooperation.
III. Other Treaty Obligations: States party to environmental treaties must take steps that also serve climate protection objectives.
IV. Law of the Sea: States must adopt measures to protect and preserve the marine environment from climate change impacts and co-operate in good faith.
V. Human Rights Law: States must respect and ensure the effective enjoyment of human rights by taking necessary steps to protect the climate system and the environment.
4. Legal Consequences for Breach of Obligations:
A breach by a State of any obligation identified above constitutes an internationally wrongful act. The responsible State is subject to the following consequences:
- Continuing Duty of Performance: The breached obligation does not lapse post-violation.
- Cessation: The State must cease ongoing wrongful actions or omissions.
- Non-Repetition: The State may be required to guarantee non-repetition of such conduct.
- Reparation: Full reparation is owed to injured States, which may include restitution, compensation (financial or otherwise), and satisfaction (acknowledgment of the wrong), provided that a sufficiently direct and certain causal nexus exists between the wrongful act and the injury.
5. Special Considerations:
Obligations Erga Omnes & Erga Omnes Partes: The Court affirmed these obligations, meaning all States have a legal interest in compliance and breaches may be invoked by all (not just directly injured) States. Attribution and Causation: For State responsibility, only actions/omissions attributable to a State count as wrongful acts. Causation requires a sufficiently direct and certain link between the wrongful act and the harm; this is to be established on a case-by-case basis
Conclusion:
The ICJ concluded that States have binding obligations under both treaty and customary international law to protect the climate system and the environment from anthropogenic GHG emissions, for the benefit of present and future generations. Failure to meet these obligations can result in international responsibility, with a range of legal consequences, including cessation, non-repetition, and reparation. The opinion underscores that all States share a common interest in meeting these obligations given the global threat posed by climate change.
[i] https://www.icj-cij.org/sites/default/files/case-related/187/187-20250723-adv-01-00-en.pdf