ICJ issues Landmark Advisory Opinion on State Obligations regarding Climate Change

On 23 July 2025, the International Court of Justice (ICJ), as the UN's principal judicial organ, issued its long-anticipated Advisory Opinion on climate change and state obligations under international law. The ICJ concluded that states' obligations to protect the climate system and the environment from anthropogenic greenhouse gas emissions (GGEs) constitute obligations erga omnes – duties owed by states to the international community as a whole. The Opinion is expected to have a significant impact on the interpretation and application of international legal norms relating to climate change and environmental protection, and to influence national policies and legal frameworks worldwide. This article provides an overview of the ICJ's key findings.

Background of the Advisory Opinion

In March 2023, the UN General Assembly adopted Resolution A/RES/77/276, requesting the ICJ to provide an advisory opinion on the scope of state obligations concerning climate change. It posed two main questions: (i) what are international state obligations to protect the climate system from anthropogenic GGEs, ensuring the well-being of both present and future generations; and (ii) what are the legal consequences for states that, through actions or omissions, cause significant climate harm, particularly concerning small island developing states and affected people? The UN's request drew upon legal instruments such as the UN Charter, the International Covenant on Civil and Political Rights, and the Paris Agreement.

In December 2024, oral hearings commenced in The Hague, with participation from 96 countries and 11 international organisations. Small island nations have been at the forefront of the initiative. The US, China, and the EU also presented positions. The ICJ allowed submissions from experts to help form an understanding of the scientific basis and impacts of climate change.

Key Findings of the ICJ

The ICJ's Opinion sets out the following key findings:

The ICJ clarified that international law applicable to the questions at hand includes the following main legal sources: (i) the UN Charter; (ii) the UN Framework Convention on Climate Change (UNFCCC); (iii) the Kyoto Protocol; (iv) the Paris Agreement; (v) the UN Convention on the Law of the Sea (UNCLOS); (vi) certain treaties related to the protection of the ozone layer; (vii) the Convention on Biological Diversity; (viii) the UN Convention to Combat Desertification; (ix) customary international law, including the duty to prevent significant harm to the environment and the duty to cooperate in environmental protection; (x) international human rights law; and (xi) key environmental principles, such as the precautionary principle.

According to the ICJ, international treaties impose the following binding obligations on states:

• Under the UNFCCC, states are obligated to adopt measures to combat and contribute to the mitigation of GGEs and adapt to climate change, and to cooperate with each other to achieve these objectives
   
• The Kyoto Protocol's provisions on binding emission reduction targets, the establishment of flexible market mechanisms, and requirements for monitoring, reporting, and verification of GGEs must be complied with.
   
• State parties to the Paris Agreement are obligated to act with due diligence by taking measures to make an adequate contribution toward achieving the temperature goal. States must also prepare, communicate, and maintain successive, progressive nationally determined contributions (NDCs) capable of limiting global warming to 1.5°C above pre-industrial levels.
   
• States have binding obligations under the Vienna Convention for the Protection of the Ozone Layer, the Montreal Protocol on Substances that Deplete the Ozone Layer and its Kigali Amendment, the Convention on Biological Diversity, and the UN Convention to Combat Desertification to ensure the protection of the climate system and the environment from anthropogenic GGEs.
   
• Under UNCLOS, states are obliged to adopt measures to protect and preserve the marine environment, including from the adverse effects of climate change, and to cooperate in good faith.
   
• Finally, states have obligations under international human rights law to respect and ensure the effective enjoyment of human rights by taking necessary measures to protect the climate system and the environment.

In addition, customary international law imposes obligations on states to ensure the protection of the climate system and the environment from anthropogenic GGEs. These obligations include the following: 

• States have a duty to prevent significant harm to the environment by acting with due diligence and using all means at their disposal to prevent activities within their jurisdiction or control from causing significant harm to the climate system and the environment, according to their capabilities.
   
• States have an obligation to cooperate with one another to prevent significant harm to the climate system and the environment.

A breach of any of these obligations constitutes an internationally wrongful act where the state is responsible. The legal consequences may include the following state obligations: 

• Cessation of wrongful actions or omissions;
   
• Providing assurances and guarantees of non-repetition of wrongful actions or omissions; and
   
• Full reparation to injured states in the form of restitution, compensation, and satisfaction, according to the law of state responsibility, including the requirement that a sufficiently direct and certain causal nexus be established between the wrongful act and the injury.

Comment

International courts and tribunals are increasingly called upon to address complex legal questions related to climate change and environmental protection. These forums have become pivotal in evaluating state obligations on issues such as rising sea levels, wildlife degradation, biodiversity loss, access to water, and extreme weather events. Among the most anticipated developments was the ICJ's Opinion on the scope of state obligations regarding climate change under international law. 

Although the ICJ's Opinion is non-binding, it establishes a foundational understanding of state responsibilities concerning climate change that may influence both international and national governance, prompting countries to adjust their environmental policies. The Opinion may also guide litigation and arbitration between states and companies – where its established principles could be invoked as legal arguments – and between companies and individuals, where legal actions might be based on its findings. Both international tribunals and domestic courts are likely to consider the ICJ Opinion in their decisions.

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