【News】 International Court of Justice advisory opinion: climate change is an “urgent and existential threat”

On July 23, 2025, the International Court of Justice (ICJ) issued an advisory opinion stating that climate change constitutes an “urgent and existential threat” and that all countries are “required to make good faith efforts” in tackling climate change. The ICJ, often referred to as the “World Court”, is the main judicial organ of the United Nations and has the authority to issue advisory opinions on specific legal issues at the request of the UN General Assembly or other bodies. The issuance of this advisory opinion stems from a request made by the United Nations General Assembly in March 2023, following an initiative led by Vanuatu. The fact that the ICJ has stated that failing to take action on climate change could constitute a breach of international law—meaning that continuing to use fossil fuels is no longer permissible—holds significant implications.

Timeline of events

March 2023: 132 countries submit joint proposal to the ICJ
Led by Vanuatu, an island nation whose very existence is threatened by sea level rise caused by global warming, a joint proposal supported by 132 countries, including Japan, was adopted as a draft resolution at the UN General Assembly.

The two key questions for which the ICJ’s opinion was sought in the resolution were:

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 [human caused] 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?
a. To states, including, in particular, small island developing States, which due to their geographical circumstances and level of development, are injured or specifically affected by, or are particularly vulnerable to, the adverse effects of climate change?
b. To peoples and individuals of the present and future generations affected by the adverse effects of climate change?

December 2024: ICJ holds public hearings
The ICJ held public hearings to hear the views of states on their obligations to international law in relation to climate change, with a view to adopting an advisory opinion. At the hearings, 96 states and 11 international organizations delivered oral statements. While some countries cautioned against measures that could lead to new regulations, island nations whose residents’ livelihoods are threatened by rising sea levels due to global warming called for stronger action.

July 2025: Advisory opinion adopted unanimously
The advisory opinion was adopted unanimously by all 15 judges at the ICJ.

Background: International efforts to address climate change

Currently, the international community is working to limit global temperature rise to 1.5°C above pre-industrial levels under the Paris Agreement. Signatories of the Paris Agreement are required to submit Nationally Determined Contributions (NDCs), implement measures to reduce emissions, and review and submit new NDCs every five years.The Global Stocktake in 2023 pointed out that the NDCs submitted by countries were insufficient to achieve the 1.5°C target, and countries were strongly urged to set more ambitious targets with the submission of new NDCs in February 2025. However, it is up to each country to decide its own targets, and there is no obligation to achieve them. The United States, the world’s second-largest CO2 emitter, announced its withdrawal from the Paris Agreement and has not submitted a new NDC, and emissions may increase further under the Trump Administration. At the 29th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP29), discussions were held on finance for climate measures in developing countries and funding for loss and damage, but many challenges remain.

People in countries with low greenhouse gas (GHG) emissions are more vulnerable to the effects of climate change and more likely to suffer damage. As climate disasters become increasingly severe each year, the United Nations General Assembly has requested the advisory opinion to aid those who are currently impacted by climate change and those who are likely to be impacted in the future.

Advisory opinions on climate change by international courts

On July 28, 2022, the United Nations General Assembly adopted a resolution declaring that access to a clean, healthy, and sustainable environment is a universal human right, and there is growing recognition of the idea that countries have an obligation to protect human rights from the adverse effects of climate change.

On May 21, 2024, the International Tribunal for the Law of the Sea (ITLOS) responded to a request from the Commission of Small Island States on Climate Change and International Law (COSIS) and issued an advisory opinion, the first of its kind from an international court, clarifying what obligations regarding climate change signatory countries have under the United Nations Convention on the Law of the Sea.The opinion stated that “marine pollution” as defined under the United Nations Convention on the Law of the Sea includes the emission of greenhouse gases, and that signatories are obligated to reduce emissions and address sea-level rise.

On July 3, 2025, the Inter-American Court of Human Rights (IACHR) published its second advisory opinion on climate-related matters, Advisory Opinion AO-32/25, addressing the climate crisis and human rights.This opinion, based on the best available science, acknowledges that the scale of the global impacts from climate change is undeniable and recognizes a “healthy climate” as a human right. It further addresses the scope of states’ human rights obligations in the context of the climate emergency, stating that “States must refrain from any conduct that reverses, delays or curtails the results of measures required to protect human rights from the impacts of climate change.”

And now, the ICJ has designated climate change as an “urgent and existential threat” to humanity and affirmed that the right to live in a “clean, healthy, and sustainable environment” is a human right. It has also indicated that climate change is subject to international human rights law and customary international law, in addition to climate change-related treaties such as the Paris Agreement. The ICJ clarified that a state’s obligations regarding climate change are determined based on international law that transcends specific climate treaties such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, indicating that governments cannot ignore their legal responsibilities.

Significance of the ICJ’s advisory opinion

The ICJ’s advisory opinion totals 140 pages in full and 40 pages in summary. Climate change is no longer merely a matter of regulating CO2 and other greenhouse gas (GHG) emissions. It has far-reaching spatial and temporal impacts, and no one, regardless of where on the planet they live, can escape its effects, including generations yet to be born. In this context, the ICJ’s clear affirmation that states are bound not only by climate change-specific treaties such as the Paris Agreement but also by obligations under customary international law and international human rights law holds significant importance.

Furthermore, the advisory opinion points out that countries are also responsible for the actions of public and private entities under their jurisdiction and control, and that if they fail to curb fossil fuel production or subsidies, they may be subject to claims for compensation from countries that have suffered damage.

The ICJ is a court, but its advisory opinions are not “judgments,” so countries are not required to comply with them. The opinions also have no legal binding force, so there is no obligation to accept the “recommendations.” However, as the opinion of an institution that expresses views on international law, it is likely to have a significant impact on future climate litigation, and may also influence negotiations where countries are urged to strengthen their climate measures. Additionally, in recent years, lawsuits have emerged worldwide that challenge governments’ climate change policies and the responsibility of companies that emit greenhouse gases, including Japan’s “Youth Climate Case Japan”. The ICJ’s advisory opinion is expected to provide momentum for such cases.

Key points of the advisory opinion

This advisory opinion states that the obligations of states to address climate change caused by anthropogenic greenhouse gas emissions are not limited to the UNFCCC, Kyoto Protocol, and Paris Agreement, but are also consistent with human rights law, maritime law, international environmental law, and other international conventions. It lists various obligations, including the following:

Addressing climate change is also important for protecting basic human rights. Under international law, the human right to a clean, healthy, and sustainable environment is essential for the enjoyment of other human rights, and therefore, all states must take ambitious measures to protect the environment, particularly the climate system.
States must cooperate in good faith to halt climate change and achieve concrete emission reduction targets.
Based on the best available scientific knowledge, all countries must set GHG reduction targets to limit the temperature rise to 1.5°C from pre-industrial levels and make every effort to achieve the 1.5°C target.
States have an obligation to protect the environment from anthropogenic GHG emissions using all means, including legal measures.
Failure by states to comply with their obligations under treaties, and failure to take measures to address climate change may constitute a breach of international law.
If states fail to take appropriate measures and are found to be in violation of international law, they may be held liable, including compensation for damages suffered by countries affected by climate change.
States have an obligation to prevent damage caused by climate change, so failing to curb the production and use of fossil fuels, the main causes of climate change, may violate international law.
Failure to adopt appropriate measures to protect the climate, including, but not limited to, halting the production, consumption, exploration licensing, or subsidisation of fossil fuels, may constitute an internationally wrongful act and is subject to further legal consequences, and could result in full reparations to injured states in the form of restitution, compensation and satisfaction.
Based on their obligations, states must continue to fulfill their obligations even if they fail to do so, for example, by adopting revised mitigation measures or enhancing carbon sinks.

It is no longer permissible to continue using fossil fuels

This advisory opinion will serve as a guideline for correcting and preventing further injustices against future generations and people who are vulnerable to climate change. At COP30, to be held in Brazil this November, there may be growing calls for developed countries with historically high emissions to take responsibility. It should also serve as a powerful tool in the ongoing fight for climate justice around the world.

If countries have a legal obligation to protect the climate and reduce anthropogenic GHG emissions from fossil fuel use, then the Japanese government’s policy of continuing to promote the use of fossil fuels, especially coal-fired power, which emits significant amounts of greenhouse gases, constitutes a violation of that obligation. It can now be said that the continued use of fossil fuels has been rejected not only by scientific knowledge but also by international law.