On 23 July 2025, all 15 Judges of the International Court of Justice (ICJ) published a landmark advisory opinion on the Obligations of States in Respect of Climate Change.

The ICJ is the highest court in the United Nations. It recognised that the consequences of climate change are severe and far-reaching, impacting both natural ecosystems and human populations. The ICJ referred to the already existing consequences (extreme weather, extinction of species, human life and health being at risk) as underscoring the “urgent and existential threat posed by climate change”.

In its 140-page advisory opinion, the ICJ responded to two questions:

1. What are the obligations on States under international law to ensure the protection of the climate system; and

2. What are the legal consequences arising from States’ acts and omissions that cause significant harm to the climate system.

In response to the first question, the ICJ concluded that all countries have a legal obligation, as matters of international environmental law, international human rights law and as part of general principles of state responsibility, to protect and prevent harm to the climate. The ICJ did address two important issues in its response on (a) attribution; and (b) causation.

a) Attribution – i.e. whether the actions of a private company (for example an oil company) could be attributed to a State. In this regard the ICJ noted that the question to be asked is whether the State is appropriately regulating private companies in line with its international obligations of due diligence and duty to protect the climate system. When asking that question, the issues of attribution do not arise. The ICJ also stated that “due diligence requires States to actively pursue the scientific information necessary for them to assess the probability and seriousness of harm” (paragraph 283).

b) Causation – i.e. whether the States actions actually caused the harm suffered. The ICJ Opinion begins by observing that causation of damage is not a requirement for the determination of responsibility (paragraph 433) but rather that an international wrongful act can be attributed to that State. However, if the question of any reparation (i.e. compensation) arises, then it must be shown that the damage for which reparation is claimed has been factually and legally caused by a State.

In response to the second question, the ICJ found that in the event of a breach of any such obligation, the State in breach must:

(i) Stop its polluting activity;
(ii) Ensure that such activities do not occur in the future; and
(iii) Make reparations to affected States.

Regarding reparations, the ICJ concluded that the appropriate nature and quantum of reparations cannot be assessed in the abstract and depends on the circumstances of a particular case (paragraph 450).

The ICJ Opinion cites heavily from international law where climate ‘harms’ can be clearly linked to major emitters and/or fossil-fuel producers and draws upon the three UN climate change treaties – the United Nations Framework Convention on Climate Change, the Kyoto Protocol and the Paris Agreement.

While the ICJ Opinion itself is not binding for governments, its opinions have significant influence both politically and legally. Further, as the ICJ Opinion itself arose from a campaign led by 27 students from the University of South Pacific, Vanuatu, it may result in more vulnerable nations that are increasingly susceptible to the effects of climate change, pushing for compensation in the international courts.