Overview and potential implications
Introduction
On 23 July 2025, the International Court of Justice (ICJ) in The Hague delivered its highly anticipated advisory opinion on States’ obligations in respect of Climate Change (Advisory Opinion). For the first time, the Court found that all States have binding legal obligations to protect the environment and combat climate change.
The Advisory Opinion is the third in a recent series of advisory opinions by international courts and tribunals addressing climate change. It follows earlier advisory opinions by the International Tribunal for the Law of the Sea (ITLOS, link) and the Inter-American Court of Human Rights (IACHR, link (Spanish only)).
In this blog, we discuss the background of the Advisory Opinion, its key findings and potential implications. We will follow up with a more detailed analysis of the Advisory Opinion separately.
Background
On 29 March 2023, the United Nations General Assembly (UNGA) by consensus adopted a resolution requesting the ICJ to render an Advisory Opinion. The resolution was introduced by a core group of States, including countries highly vulnerable to the adverse consequences of climate change, such as the small island group, Vanuatu.
The ICJ was asked to answer the following questions:
- 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 for States and for present and future generations?
- What are the legal consequences under these obligations for States where they, by their acts and omissions, have caused significant harm to the climate system and other parts of the environment, with respect to:
- States, including, in particular, small island developing States, which due to their geographical circumstances and level of development, are injured or specially affected by or are particularly vulnerable to the adverse effects of climate change?
- Peoples and individuals of the present and future generations affected by the adverse effects of climate change?
During the advisory proceedings, both States and international organizations (Participants), such as the Organization of the Petroleum Exporting Countries (OPEC), Vanuatu, China, India, the EU and the World Health Organization (WHO), submitted numerous written statements/comments (i.e. 91 written statements and 62 written comments) and 107 Participants presented oral statements during the oral hearings. The ICJ also met with scientists of the Intergovernmental Panel on Climate Change (IPCC).
Key findings
For the first time, the ICJ found that States have a legally binding obligation to protect the climate system from the harmful effect of greenhouse gas emissions (GHG) and that a breach of this obligation is an internationally wrongful act, entailing State responsibility. Even States that are not parties to climate treaties have a duty to address climate change under customary international law. The ICJ also recognised that a clean, healthy and sustainable environment is a human right.
State obligations
The ICJ noted that States parties to the major climate change and environmental treaties have binding legal obligations to protect the environment, including addressing climate change. These duties stem inter alia from international climate and environmental treaties such as the UNFCCC, the Kyoto Protocol and the Paris Agreement, international human rights law, as well as customary international law (i.e. the duty to prevent significant harm to the environment and the duty to co-operate for the protection of the environment).
The Court found that State obligations under the climate change treaties include adopting measures to reduce GHG emissions and to adapt to climate change and that all States are required to cooperate to achieve these objectives and to share technologies, financial resources and information. Developed countries are expected to take the lead in combating climate change and support adaptation efforts in developing and vulnerable States. The ICJ says further that Nationally Determined Contributions (NDCs) – the climate action plans that States parties to the Paris Agreement are required to prepare and improve – constitute binding obligations of conduct for States. Failure to draft and maintain these NDCs is considered an internationally wrongful act. NDCs must be ambitious and capable of limiting global warming to the target of 1.5 °C.
Under customary international law, even States that are not parties to climate treaties have a duty to protect the environment and combat climate change. Furthermore, the ICJ recognised that a clean, healthy and sustainable environment constitutes a human right.
Legal consequences
A breach of any of these obligations constitutes an internationally wrongful act, for which the respective State is responsible. Legal consequences for any breaches may include:
- duty to cease the harmful conduct;
- provide assurances and guarantees of non-repetition; and
- grant full reparation of the damage caused –in the form of restitution, compensation, and satisfaction.
According to the ICJ, any State can be held accountable for breaches of the climate change obligations identified in the Advisory Opinion, regardless of whether they have caused harm directly or indirectly and, because of the erga omnes character of the obligation, any State may invoke responsibility for such breach. Attribution in this context refers to a State’s own failure to take the necessary regulatory and legislative measures to limit GHG emissions – including those of the private sector. Therefore, the 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 licences or the provision of fossil fuel subsidies may constitute an internationally wrongful act.
Furthermore, each injured State (e.g. small island States such as Vanuatu) can hold respective States responsible for breaches of relevant obligations. Individuals’ rights to hold a State legally responsible or to bring a claim for harm resulting from a breach of a State’s obligations will depend on the relevant primary obligations of the States involved. Whether individuals are entitled to invoke a State’s responsibility is subject to the specific treaties and other legal instruments that create procedural and substantive rights and obligations governing the relationship between the States and relevant individuals.
Observations and potential implications
Although the Advisory Opinion is not legally binding, it is expected and intended to offer authoritative guidance on the scope and content of States’ obligations under international law in relation to climate change.
Importantly, while the Advisory Opinion only deals with States’ obligations, it will nevertheless likely be said to be relevant more generally. As some claimants, courts, regulators and other bodies increasingly refer to international law principles to assess corporate conduct – particularly in the context of climate and ESG litigation – we expect that the Advisory Opinion will feature prominently in future climate change related proceedings.
Furthermore, as the ICJ has now – for the first time – clearly stated that States do indeed have a legal obligation under international law to address climate change and may be held responsible, it is possible that States will impose even more stringent rules relating to GHG emissions on private operators than before in order to comply with their own legal obligations internationally (i.e. likely a trickle-down effect).
The Advisory Opinion builds on a number of cases in other courts where human rights-based arguments have been used to assert a right to a clean, healthy and sustainable environment (often based upon the right to life and/or the right to a private life). Indeed, the ICJ’s opinion lends support to a new human right to a clean, healthy and sustainable environment. In light of this, the emerging supply chain human rights laws – including the EU’s Corporate Sustainability Due Diligence Directive (CSDDD) – that essentially require corporations to respect human rights and avoid and remediate any human rights violation linked to their businesses could lead to evolving corporate compliance obligations with respect to climate change mitigation too.
In light of the above, it is anticipated that the Advisory Opinion will influence ongoing and future legal proceedings. It is expected that it will be primarily used in proceedings against States, but it may also be used in challenges to companies with claimants and other bodies seeking to rely on and extend the application of the Advisory Opinion.
