On March 29, 2023, the United Nations General Assembly (UNGA) adopted a resolution requesting an advisory opinion from the International Court of Justice (ICJ) on States’ obligations regarding climate change. This request was widely seen as an opportunity for the Court to clarify States’ legal obligations, advance climate justice, and protect the environment for present and future generations.
The UNGA requested the ICJ render an opinion on the following questions:
(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 gasses (GHG) 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?
The request happened in parallel to similar advisory opinion processes before the International Tribunal for the Law of the Seas (ITLOS) and the Inter-American Court of Human Rights (IACtHR). ITLOS published its advisory opinion in May 2024, and the IACtHR opinion is expected later in 2025. These ‘competing’ perspectives on climate change by international and regional courts and tribunals can significantly advance international climate law.
This blog post is Part 1 of a three-part series highlighting the main legal arguments presented during the ICJ hearings. Part 1 (i) provides background on the written submissions received by the ICJ and participation in the hearing, (ii) discusses arguments regarding the law that should be considered by the ICJ in determining states obligations regarding climate change, and (iii) explores the relevance of the no-harm rule under customary international law, in particular.
Background on the Developments before the ICJ Advisory Opinion
The ICJ proceedings had an unprecedented level of participation. The Court received 91 written statements and 62 written comments on those statements, and 96 States and 11 international organizations presented oral statements at public hearings in the Hague in December 2024. Some of the participating States appeared before the ICJ for the first time in history. Non-governmental organizations and youth groups also widely covered the oral proceedings.
During the hearings, States and organizations presented their views on the two questions posed by the UNGA and, in some cases, provided evidence and powerful testimonies regarding the widespread impacts of climate change. A myriad of statements also emphasized the importance of advancing climate justice, the need to acknowledge the historical responsibility of some States for climate change, and the disproportionate burden climate change is imposing on those least responsible for it.
Most participants agreed that greenhouse gas emissions must be reduced and urgent measures must be taken to meet the goals of the Paris Agreement. However, distinct perspectives emerged on how the ICJ should respond to the legal questions.
State Responsibilities in Climate Change: What Law Applies?
Some of the most relevant discussions in the ICJ hearings revolved around the applicable law or, in other words, which law is appropriate to determine the legal obligations of States regarding climate change and the consequences under those obligations for States that ‘have caused significant harm to the climate system and other parts of the environment.’
The UNGA’s resolution asked the Court to have ‘particular regard’ for 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 (UNFCCC), the Paris Agreement, the United Nations Convention on the Law of the Sea (UNCLOS), the Universal Declaration of Human Rights, the duty of due diligence, the principle of prevention, and the duty to protect and preserve the marine environment. Despite this guidance, submissions to the ICJ reflected two opposing views on the body of law that should be considered: (i) a narrower view focused solely on the UNFCCC and the Paris Agreement, and (ii) a broader view expanding the applicable law beyond climate treaties.
States arguing for a narrower approach included China, Germany, Kuwait, Russia, Saudi Arabia, the Nordic countries, the United Kingdom, and the United States. For instance, Germany contended that the Paris Agreement and the UNFCCC are ‘the decisive treaties’ to determine the obligations of States in the context of climate change. Similarly, Saudi Arabia argued that the ‘chapeau’ of the UNGA’s resolution does not affect the Court’s function of determining the applicable law and that ‘the specialized treaty regime on climate change provides a complete answer to the questions’ before the Court.
The United States, Kuwait, and the United Kingdom, among others, also contended that the legal obligations of States regarding climate change are mainly outlined in the Paris Agreement. Some States even argued that the climate treaties constitute lex specialis and lex posterior. For instance, Russia asserted that the ‘treaties of the UNFCCC system should be considered the legal basis for regulation and lex specialis in the area of combating climate change.’ Similarly, China argued that the UNFCCC and the Paris Agreement are lex specialis and the ‘tailor-made’ regime on climate change that should guide the Court’s deliberations. In this context, the Nordic countries added that the Paris Agreement ‘is both the latest treaty and the treaty with the most precisely delimited scope of application’ and that ‘the most recent consensus amongst the State parties to the UN climate change regime shall take precedence” under the principle of lex posterior.
In contrast, several States argued that the climate treaties are not the only relevant sources of law. These include mostly Global South countries such as Antigua and Barbuda, Belize, Bolivia, Barbados, Colombia, Kenya, Samoa, Vanuatu, and the Melanesian Spearhead Group (MSG).
In particular, Vanuatu and the Melanesian Spearhead Group (MSG) highlighted that States have obligations under international law to act with due diligence, prevent significant environmental harm, protect human rights, and protect and preserve the marine environment. They also underscored the importance of the right to self-determination as a peremptory norm of international law, considering that climate change deprives people of their traditional territories, cultures, political systems, and means of self-governance. Several domestic cases brought by Indigenous groups make similar claims.
Antigua and Barbuda, Belize, Bolivia, Barbados, Colombia, and several other States presented similar arguments, emphasizing that the legal obligations of States go beyond the UNFCCC and the Paris Agreement. Antigua and Barbuda even contended that ‘many high-emitting States attempt to rely on the climate treaties as a shield to escape accountability.’ Kenya also added that there were several attempts ‘to smuggle the lex specialis argument through the back door.’
In this context, Mexico and other States highlighted that, for lex specialis to apply, ‘there must be clear conflicts or explicit intent to exclude other norms’ and that none exist in the context of climate treaties. Several representatives also emphasized that the climate treaties do not override customary international law and ‘foundational principles’ like the no-harm rule. For instance, Samoa argued that several treaties, rules, and principles of international law ‘were in operation for much, if not the entirety of the period during which States have been causing significant harm to the climate system and other parts of the environment.’
Significantly, ITLOS addressed this issue in its advisory opinion (albeit within the context of UNCLOS), and rejected the interpretation of the Paris Agreement as lex specialis with respect to the impacts of climate change on oceans (see here, here, and here). While it is possible that the ICJ will take a different approach to the topic, it is likely that the Court will attempt to harmonize the interpretation of international climate change law with the views of the ITLOS and the IACtHR.
Numerous States emphasized the importance of integrating international treaties, human rights law, and customary international law to address the questions before the ICJ. Several States also pointed out that these sources must be interpreted considering the principle of systemic integration under Article 31 (3)(c) of the Vienna Convention on the Law of Treaties (VCLT), similar to how ITLOS interpreted it. This requires the interpreter of a treaty to consider any relevant rules of international law that are applicable.
No-harm Rule
The discussion of the application of the no-harm rule was particularly notable. Several States emphasized that they have a duty to ensure that activities conducted within their territories do not cause transboundary environmental harm to other countries. According to States such as Bolivia, Costa Rica, Dominica, Kiribati, and Mexico, the no-harm rule applies in the context of climate change and requires States to take all necessary measures to ensure that greenhouse gas emissions do not cause harm to the environment of other States.
However, Australia argued that the principle of prevention does not apply to harm caused by greenhouse gas emissions. Australia characterized these emissions as ‘materially different from the conventional case of transboundary harm’ and asserted that the ICJ has only applied the principle of prevention in those conventional cases. Australia further emphasized that those cases ‘involve a direct and temporally proximate cause of environmental harm from an identifiable source spreading from one State to a neighboring State, such as discharge of pollution into a river.’
Similarly, the Nordic countries claimed that the standard in cases dealing with transboundary environmental harm was ‘primarily developed within the framework of bilateral relations between States.’ They contended that this standard cannot be applied to multi-source harms like climate change due to the absence of state practice and opinio juris. In response, States such as Bolivia, Costa Rica, The Gambia, and Kiribati emphasized that the principle of prevention is not restricted to bilateral or localized pollution cases, but rather applies to all instances of significant harm.
Jorge Alejandro Carrillo Bañuelos
Jorge Alejandro Carrillo Bañuelos is the Sabin Center's rapporteur for the International Court of Justice.
Dr. Maria Antonia Tigre is the Director of Global Climate Litigation at the Sabin Center for Climate Change Law at Columbia Law School.
