The International Court of Justice (ICJ or Court) delivered its landmark advisory opinion on 23 July 2025 in Obligations of States in respect of Climate Change.
The UN General Assembly had asked the ICJ to identify the legal 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”.
The ICJ unanimously declared that States have legally binding obligations under international law to protect the climate system and other elements of the environment from greenhouse gas emissions. These obligations arise from climate treaties and also from customary international law and human rights law. States owe climate protection duties to the international community as a whole, even when they are not party to specific climate treaties. They must act to prevent foreseeable climate harm or face international legal responsibility.
While the ICJ’s opinion itself is not binding – on States, itself or on domestic courts – it carries considerable legal weight and political legitimacy. It is persuasive authority in interpreting international instruments and States’ obligations under international law and is expected to influence climate litigation and domestic policy.
Key findings include:
- 1.5°C is the primary agreed-upon legally binding target for limiting the global average temperature increase under the Paris Agreement.
- Customary international law imposes binding obligations on States to take preventive and precautionary measures to avoid climate harm. These measures must take account of science and international standards. The standard of due diligence is stringent.
- The conduct of States relevant to the Opinion includes actions which directly result in GHG emissions but also consumption and production activities, such as on-going production, the approval of new exploration licences and the subsidising of fossil fuels.
- It also includes the actions of non State actors, such as fossil fuel companies within the effective control of the State. States must regulate emissions of non State actors as part of their due diligence obligations.
- Both customary international law and climate treaties, such as the UN Framework Convention on Climate Change and the Paris Agreement, impose binding obligations on States to undertake adaptation measures in line with the best available science.
- Scientific evidence allows emissions to be attributed to individual States, including cumulative historical and current emissions. This enables States harmed by climate change to invoke legal responsibility. All States have a legal interest in compliance and, as such, any State – not only those harmed directly – can invoke responsibility for breaches of climate obligations under customary international law and climate treaties.
The Advisory Opinion has consequences for Australia, which is the second largest exporter of coal and gas in the world and is continuing to approve new fossil fuel projects. Australia has not restricted its fossil fuel production in line with the temperature goal of 1.5°C. In light of the Advisory Opinion, these policy settings could expose Australia to claims that it has failed to fulfil its international law obligations to protect the climate system from anthropogenic GHG emissions.
The Advisory Opinion and the Court’s summary can be read here. In the words of the Court: “…the questions posed by the General Assembly 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.”