States must protect the global climate system: the historic advisory opinion of the International Court of Justice

Traduzione di Elena Ciullo

On 23 July 2025, the International Court of Justice issued a landmark advisory opinion on international environmental law and climate justice. For the first time, the UN judicial body has clearly stated that states have legally binding climate obligations and that, in case of violation, they would commit an unlawful act and could be called upon to compensate the most affected states.

The pronouncement stems from a request made by some students of Vanuatu (an archipelago in the Pacific Ocean) to the General Assembly of the United Nations which, pursuant to art. 65 of the Statute of the Court, referred the matter back to the Court (resolution 77/276), requesting an advisory opinion on two fundamental questions:

1. What are the obligations of states under international law to ensure the protection of the climate system and other parts of the environment from greenhouse gas emissions, towards other states and present and future generations;
2. What are the legal consequences of such obligations for states that, through their actions or omissions, have caused significant damage to the climate system and other parts of the environment, with reference to:(i) states, in particular small island developing states, which, because of their geographical location and level of development, are particularly affected by, or vulnerable to, the adverse effects of climate change; (ii) peoples and individuals belonging to present and future generations who are affected by the adverse effects of climate change.
3. Obligations under the climate change treaties:
4. States parties to the United Nations Framework Convention on Climate Change (UNFCCC) must take measures to reduce emissions and adapt to climate change, and cooperate with each other to achieve the objectives of the Convention;
5. The UNFCCC Annex I states (industrialised countries) must take a leading role in combating climate change;
6. States parties to the Kyoto Protocol must comply with its provisions;
7. States parties to the Paris Agreement have an obligation to act with due diligence according to the principle of common but differentiated responsibilities, submit and update nationally determined contributions (NDCs) in order to help contain the rise of global temperature within 1.5°C, implement concrete measures to achieve the objectives set out in the NDCs, cooperate and support each other through technology and financial transfers, in good faith.
8. Obligations under other environmental treaties:
9. Obligations under customary international law:
10. Obligations under international human rights law:

During the written phase of the legal action, 91 written submissions and 62 written observations from States and international organisations were lodged at the Registry. The Court held public hearings between 2 and 13 December 2024, during which 96 States and 11 international organisations presented oral statements.
This is the highest level of participation in a case in the history of the Court.

In addition, the Advisory Opinion was adopted unanimously, an event that occurred only five times in almost 80 years.

When it comes to the first question, the Court listed the following obligations.

States parties to conventions such as those on ozone, biodiversity, desertification and the UN Convention on the Law of the Sea have obligations to protect the climate and marine environment.

States, even those not party to the treaties, must prevent significant damage to the environment by acting with due diligence and using all means at their disposal. They must also cooperate in good faith and on an ongoing basis to prevent such damage.

States must take measures to protect the climate and the environment also in order to ensure the full enjoyment of human rights. The Court stresses that environmental protection is now an integral part of the enjoyment of human rights.

States, including those not parties to the traty, have therefore real legal obligations towards other states and present and future generations.

In response to the second question of the UN, the Court held that a State’s breach of any of the obligations set out in its answer to the first question constitutes an internationally wrongful act entailing the international responsibility of that country. The legal consequences arising from the commission of an internationally wrongful act may include the obligation to:

a) put an end to the wrongful conduct if the conduct is prolonged;
b) provide guarantees of non-repetition, if circumstances so require;

c) guarantee full reparation to the injured States, in the form of restitution, compensation and satisfaction, provided that a sufficiently direct and certain causal link between the unlawful act and the damage suffered is prooved.

"Climate degradation caused by greenhouse gas emissions is an urgent and existential threat," said Justice Yuji Iwasawa, President of the International Court of Justice.

"This is a victory for our planet, for climate justice and for the power of young people to make a difference," said UN Secretary-General António Guterres.

This opinion, although not binding, is of historical significance: it not only outlines the obligations of states in relation to the climate crisis, but also specifies the content of liability in case of breach; In addition, the Court states that the right to a healthy environment is an integral part of fundamental human rights.

Despite the revolutionary scope of the opinion, its concrete impact will also depend on the world’s political will. There are still several political leaders who deny the climate crisis, hindering the adoption of effective measures to contain it. In addition, several climate protests are being repressed: in Italy, for example, the Security Law increases penalties for demonstrators, targeting forms of civil disobedience used by environmental movements. The risk, as always, is that international law remains on paper, while reality develops in the opposite direction, depending on who governs at a given historical moment.