The UN highest court has delivered its much-anticipated advisory opinion clarifying the obligations of States with respect to climate change as well as the legal consequences for breaching these obligations. The Advisory Opinion, which the International Court of Justice (ICJ) adopted unanimously, considers the 1.5°C threshold to be the primary agreed temperature goal under the Paris Agreement on climate change and notes that even a warming of 1.5°C is not considered safe.
Yuji Iwasawa, President of the Court, read a summary of the Advisory Opinion in a public sitting on 23 July 2025. Civil society organizations (CSOs) held a livestream of the reading outside the Peace Palace in The Hague, the Netherlands, where the Court resides, and in various other cities, the Earth Negotiations Bulletin (ENB) briefing note reports.
The Advisory Opinion, ENB writes, “is the culmination of a two-year-long process that has seen record-breaking participation by States and international and regional organizations and strong engagement by legal scholars and civil society representatives from around the world.” It underscores the role of the Intergovernmental Panel on Climate Change (IPCC) in providing best available science and, with regard to nationally determined contributions (NDCs) under the Paris Agreement, emphasizes that:
- their content, which is key to assess compliance, is not entirely up to parties’ discretion;
- parties have to do their utmost to ensure their respective NDCs represent the highest possible ambition, with the exact standard depending on aspects such as the countries’ contribution to cumulative greenhouse gas (GHG) emissions and their level of development and national circumstances;
- NDCs must, when taken together, be capable of achieving the temperature goal and purposes of the Paris Agreement; and
- parties have an obligation to undertake best efforts to achieve their NDCs.
The Court clarifies that, in addition to the climate treaties, States’ obligations stem from human rights law and customary international law, regardless of whether a State is a party to the climate change treaties. “This finding is significant in the light of possible withdrawal of certain countries from the climate treaties, as exemplified by the US’s withdrawal from the Paris Agreement,” ENB writes.
The Advisory Opinion emphasizes that a State’s failure to take appropriate action to protect the climate system from GHG emissions – including those due to 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 attributable to that State.
It further notes that a State may be considered responsible for not taking the necessary regulatory and legislative measures to limit the emissions released by private actors under its jurisdiction or control.
While the Court makes no pronouncement on the responsibility of individual States, noting that such responsibility has to be assessed on a case-by-case basis, the Advisory Opinion lays out the available legal remedies, including non-repetition, restitution, and compensation.
The Advisory Opinion also underscores that:
- States parties to the Paris Agreement have obligations of adaptation and cooperation, including through technology and financial transfers, which must be performed in good faith;
- the human right to a clean, healthy, and sustainable environment is essential for the enjoyment of other human rights; and
- once a State is established, the disappearance of one of its constituent elements would not necessarily entail the loss of its statehood, which is important for small island States whose territorial integrity is threatened by sea level rise.
While the Advisory Opinion and all its operative clauses were adopted unanimously, the judges appended several separate opinions and declarations, providing further insights into the Court’s deliberations.
On 29 March 2023, the UN General Assembly (UNGA) adopted a resolution, deciding on the questions to be put to the ICJ, namely:
- 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 GHG emissions 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: a) States, including small island developing States (SIDS), 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? b) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?
In its reflections on the proceedings, the Court notes that the questions posed by the UNGA represent more than a legal problem: they concern an existential problem of planetary proportions that imperils all forms of life and the very health of our planet.
The Alliance of Small Island States (AOSIS) welcomed the Advisory Opinion as “a global affirmation that climate harm is not just unjust, it is unlawful,” pledging to carry it into “every negotiation, every courtroom, and every call for justice.” The Pacific island State of Vanuatu that spearheaded the request for the Advisory Opinion announced the preparation of a resolution to take back to the UNGA. The UN Secretary-General lauded it as “a victory for our planet, for climate justice, and for the power of young people to make a difference.” Human rights advocate Mary Robinson stated the Advisory Opinion “ushers in a new era of accountability for major emitters.”
“The following months and years will show whether and how countries and stakeholders will give effect to the Advisory Opinion and which means they will see fit to do so,” the ENB briefing note’s preliminary outlook highlights. [ENB Coverage of the Delivery of ICJ Advisory Opinion on the Obligations of States in Respect of Climate Change]
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This news story is part of a project that seeks to raise awareness and build momentum and knowledge around the ICJ advisory opinion on obligations of States in respect of climate change and to promote a better understanding of the implications of the advisory opinion among sustainable development decision makers.