Summary:
On 29 March 2023, the United Nations General Assembly (UNGA) adopted a resolution requesting an advisory opinion from the International Court of Justice (ICJ) to clarify States’ international obligations concerning climate change. This resolution, Res. A/77/L.58, was prepared on the initiative of the Government of Vanuatu, and was adopted by consensus by the UNGA. This request led to the largest (in terms of participants) proceedings before the ICJ to date, with 97 States and 11 international organisations making written or oral submissions. On 23 July 2025, the ICJ issued its advisory opinion, which was immediately received as a historic and landmark contribution to clarifying the international obligations of States regarding climate change.
Background:
In September 2021, during the UN General Assembly’s annual meeting, the Prime Minister of the Republic of Vanuatu, Hon. Bob Loughman Weibur, announced that the country would build a coalition of States to seek an advisory opinion on climate change from the International Court of Justice (ICJ). The initiative received support from a large number of co-sponsoring states.
The proposal aims to contest “environmental devastation and large-scale violations of human rights for the most vulnerable”. Under the slogan of “bringing the world’s biggest problem to the world’s highest court”, this initative was originally spearheaded by a group of students from the University of the South Pacific. By July 2022, the alliance behind the initative included over 1500 civil society organisations in 130 countries. It also received the endorsement of the Organisation of African, Caribbean, and Pacific States (OACPS).
In July 2022, Vanuatu’s Minister of Climate Change, Hon. Silas Bule Melve, clarified the country’s ambitions for the advisory opinion. He stated that “[t]his is not a court case, and we do not seek to assign blame. But we do seek a credible way to bolster climate ambition moving forward to save the Paris Agreement and our blue planet”. The Republic’s legal team in this endeavor is led by Julian Aguon and Margaretha Wewerinke-Singh of the Pacific law firm Blue Ocean Law.
This approach follows an earlier initiative from 2012, by Palau and the Republic of the Marshall Islands, which did not manage to rally a majority of General Assembly members in suport of presenting a question concerning climate change to the ICJ.
Question put to the ICJ:
The resolution was adopted by the UN General Assembly on 29 March 2023. It decided, in accordance with Article 96 UN Charter, to request the ICJ, pursuant to Article 65 of its Statute, to render an advisory opinion on the following question:
“Having particular regard to the Charter of the United Nations, the International Covenant on Civil and Political Rights, the International Covenant on Economic, Social and Cultural Rights, the United Nations Framework Convention on Climate Change, the Paris Agreement, the United Nations Convention on the Law of the Sea, the duty of due diligence, the rights recognized in the Universal Declaration of Human Rights, the principle of prevention of significant harm to the environment and the duty to protect and preserve the marine environment,
(a) 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;
(b) 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:
(i) 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?
(ii) Peoples and individuals of the present and future generations affected by the adverse effects of climate change?”
Interim developments:
On 25 April 2023, the President of the ICJ made an Order organizing the proceedings and fixing time limits for written submissions by States and international organisations in this case.
In June 2023, the Court authorized the European Union, the Commission of Small Island States on Climate Change and International Law and the International Union for Conservation of Nature to participate in the proceedings.
On 26 November 2024, preceding its oral hearings in these proceedings, the Court held an expert hearing with a group of past and present authors of the reports of the Intergovernmental Panel on Climate Change (IPCC), aiming “to enhance the Court’s understanding of the key scientific findings which the IPCC has delivered through its periodic assessment reports covering the scientific basis, impacts and future risks of climate change, and options for adaptation and mitigation.”
Oral hearings:
From December 2-13 2024, the ICJ held oral hearings in these proceedings. The proceedings included involvement from 97 states and 11 international organizations, making them the ICJ’s most extensive to date, and for some States marking their first-ever involvement with the Court.
The written comments received by the Court (91 written statements as well as and 62 comments on those same statements) were made available online during the course of the proceedings alongside verbatim reports of the oral interventions made and a video livestream.
The written and oral proceedings covered a wide range of topics, from the meaning of CBDR-RC and equity, to the recognition of the human right to a healthy environment, to the interplay between international climate law and other areas of international law (e.g. its relationship with human rights frameworks), with some States arguing that the former represented a lex specialis to the latter that precluded further-reaching obligations under human rights law.
Several judges also asked questions during the oral proceedings, to which the participants were given leave to reply.
Advisory opinion of 23 July 2025:
In its advisory opinion, which can be read in full below, the ICJ was concerned with identifying the most directly relevant applicable law concerning the international obligations of States in the context of climate change. As this was not a contentious case, it did not apply the law to the context of a specific State.
The opinion covered a broad range of aspects: from asserting the role of climate science for the law, to confirming non-refoulement obligations and the ITLOS findings on greenhouse gas emissions as marine pollution, to holding that sea-level rise does not deprive countries of marine or land territory or their statehood. The below sets out core aspects of the opinion in a non-exhaustive way.
First, importantly, the Court did not accept the lex specialis argument made by some states to try to insulate climate change from all obligations except for those enshrined in the climate treaties (and particularly the Paris Agreement). The Court found that the relevant international instruments complement each other, and that it could not find any actual inconsistencies between the climate treaties and other relevant rules of international law. This meant that the Court considered various areas of law applicable, and found that States have obligations under the climate treaties but also under customary law, environmental treaties, and human rights law. In doing so, the Court held that the international law enshrines binding obligations also for states that terminate their membership in the Paris Agreement.
The ICJ’s opinion extensively examines the obligations contained in the international climate law framework. In doing so, it considered the temperature target that States must try to stay below. The Court interpreted the Paris Agreement based on COP decisions (which, it held, represent “subsequent agreements” under the VCLT) and in doing so recognized the 1,5 degree warming threshold as States’ primary goal, over the 2 degree warming threshold also enshrined in Article 2 of the Paris Agreement. Moving to mitigation, the Court held that that Paris Agreement requires States to set out a nationally determined contribution (NDC) based on stringent standard of due diligence. Rejecting the argument that these could not be subjected to any substantive review, it held that NDCs must satisfy certain standards under the Paris Agreement and that the NDCs of all States must, when taken together as a group, be capable of realizing the objectives of the Agreement as set out in article 2 (the 1,5 degree temperature goal).
The Court also examined the adaptation obligations under the Paris Agreement. It held that States have legally binding obligations to take adaptation planning actions. The fulfilment of these adaptation obligations is to be assessed against a standard of due diligence. That means that it is incumbent on States parties to the Paris Agreement to take measures that can enhance adaptive capacity and reduce vulnerability to climate-related impacts.
Turning to obligations under customary international law, including the prohibition of significant transboundary environmental harm (the ‘no harm’ rule), the Court held that this obligation applied to the context of climate change, and was not restricted to territorially limited, local situations. The Court recognized that the standard of due diligence for preventing significant harm to the climate system is stringent. This meant that States are expected to display a heightened degree of vigilance and that preventive measures are required. Customary international law, the Court held, also enshrines a duty for States to cooperate with each other. In addition, the Court flagged principles of sustainable development, CBDR-RC, equity, intergenerational equity, precautionary principle as applicable guiding principles.
On human rights law, the Court held that a wide range of human rights were at risk in the context of climate change. Concerning the applicability of human rights obligations, it held that these were not displaced by the climate treaties as a lex specialis. Instead, it held that “the core human rights treaties, including the ICESCR [International Covenant on Economic, Social and Cultural Rights] and the ICCPR [International Covenant on Civil and Political Rights], and the human rights recognized under customary international law form part of the most directly relevant applicable law” (para. 145). It went on to find that international human rights law must inform States’ obligations under other sources of obligations, including the climate treaties and customary international law, and vice versa, in the interest of a harmonized interpretation (para. 404). The Court also recognized the importance of the right to a healthy environment, which it described as “inherent in the enjoyment of other human rights” (para. 393). It also indicated that human rights norms could potentially apply extraterritorially.
The Court also made various findings concerning reparations, although not aimed directly ad human rights law or individual redress. It held that the main mitigation obligations set forth in the climate change treaties apply erga omnes and applied the customary rules on reparations (ARSIWA). Notably, it also emphasized the existence of production-side obligations (“[f]ailure of a State 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 which is attributable to that State” (para. 427).
Full text of the advisory opinion:
Further reading:
- For more on Vanuatu’s original initiative, see here.
- For a summary and analysis of the initiative before the advisory opinion was issued, see the post on our blog by Pranav Ganesan.
- For analysis of the advisory opinion, see our blog symposium:
- Viktoriya Gurash, ‘Does the ICJ Ignite States’ ‘Appetite’ for Climate Damages Claims?‘
- Pranav Ganesan, ‘The ICJ’s Interpretation of the Paris Agreement‘
- Violetta Sefkow-Werner, ‘The ICJ’s Advisory Opinion on Climate Change: Treaty and Custom – A Marriage with a Complicated Matrimonial Regime‘.
- For a discussion of human rights in the ICJ advisory opinion and a comparison with the recent findings of the IACtHR, see Corina Heri’s post on Verfassungsblog, here.
Suggested citation:
International Court of Justice, advisory opinion regarding the obligations of States in respect of climate change, 23 July 2025, no. 187.
Last updated:
3 October 2025.