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Obligations of States in Respect of Climate Change, Advisory Opinion, 2025 I.C.J. (23 July 2025)
In a 2025 Advisory Opinion, the International Court of Justice (ICJ) made it clear that States must do more to address climate change. The Opinion provides authoritative interpretations of existing international law, underscoring the legal duties of States in addressing the climate crisis and its devastating environmental and human rights impacts, and offering guidance for future legal action and accountability. The ICJ expressed deep concern about the climate emergency and affirmed that all States have legal obligations to address the crisis.
Highlights of the International Court of Justice Advisory Opinion
The ICJ gave its advice on two questions referred to it by the UN General Assembly:
(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:
Obligations of States in Respect of Climate Change, Advisory Opinion, 2025 I.C.J. (23 July 2025), para. 1 (citing United Nations General Assembly resolution 77/276 (29 March 2023)).
The Court considered the written and oral submissions of many States, international organizations, and civil society organizations before issuing its Advisory Opinion. The Advisory Opinion unanimously affirmed that States have various legal obligations in respect of climate change, including the obligation to prevent significant harm to the environment.
The Court opined that the applicable law to determine the obligations of States in respect of climate change included not only climate change treaties, but also other conventions and treaties, customary international law, and international human rights law, and principles such as common but differentiated responsibility and the precautionary principle as guiding principles for interpretation. Id. at paras. 113-173.
Among other conclusions with respect to obligations under climate change treaties, the Court took the view that although the Paris Agreement provides for limiting the global average temperature increase to well below 2°C above pre-industrial levels as a goal and 1.5°C as an additional effort, scientifically based consensus and subsequent agreements by State parties support the interpretation that 1.5°C is the agreed primary temperature goal for limiting the global average temperature increase under the Paris Agreement. Id. at para. 224.
The Court also opined that States have a legal obligation to submit regular Nationally Determined Contributions required under the Paris Agreement, which should be progressive – meaning increased efforts and measures to reach the 1.5°C standard. Id. at paras. 234 et seq. and 240 et seq. The Court also found that States have a legal obligation to cooperate in areas including adaptation and loss and damage, as established in the Paris Agreement. Id. at paras. 260 et seq. The Court notes that UNFCCC Article 4 requires all parties to “[d]evelop, periodically update, publish and make available. . . national inventories of anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled by the Montreal Protocol. . .” and that this is a legally binding obligation. Id. at paras. 201-02.
Additionally, the Court, having examined customary international law, opined that States are legally obligated to prevent significant harm to the environment and to the climate system, as well as to ensure that their actions and omissions do not cause harm to other States through their greenhouse gas emissions. Id. at paras. 272 et seq.
Reviewing international human rights law, the ICJ affirmed that the environment “is the foundation for human life, upon which the health and well-being of both present and future generations depend” and, therefore, “the protection of the environment is a precondition for the enjoyment of human rights.” Id. at para. 373 (internal citations omitted). More specifically, the ICJ acknowledged that “[t]he degradation of the climate system and of other parts of the environment impairs the enjoyment of a range of rights protected by human rights law” and that “the adverse effects of climate change, including, inter alia, the impact on the health and livelihoods of individuals through events such as sea level rise, drought, desertification and natural disasters, may significantly impair the enjoyment of certain human rights.” Id. at paras. 375-76. The human rights harmed by climate change as considered by the Court include the rights to life, health, an adequate standard of living, privacy, family and home, and the rights of women, children, and indigenous peoples. Id. at paras. 377-82. Furthermore, States have obligations to ensure the effective enjoyment of these rights. Id. at para. 371 (see also id. at paras. 377-79, 381). Finally, the ICJ concluded that “States have obligations under international human rights law to respect and ensure the effective enjoyment of human rights by taking necessary measures to protect the climate system and other parts of the environment.” Id. at para. 457(3)(E).
Addressing the second question of legal consequences for non-compliance, the Court said that a State in breach of any of its climate obligations is internationally responsible for a wrongful act, which implies the duty to cease the wrongful actions or omissions, to guarantee they don’t repeat the actions, and to provide full reparation to injured States. Id. at paras. 407 et seq.
The ICJ affirmed that both State action and inaction that contribute to climate harm may constitute breaches of obligations under international law, triggering legal responsibility, noting:
Failure 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. . . . [A] State may be responsible where, for example, it has failed to exercise due diligence by not taking the necessary regulatory and legislative measures to limit the quantity of emissions caused by private actors under its jurisdiction.
Id. at paras. 427-28. The ICJ outlines the legal consequences that may arise from wrongful acts, implicitly recognizing the justiciability of a State’s climate action or inaction. See id. at paras. 444-455 (see also id. at paras. 425-38, on the nature of attribution and causation in climate cases; para. 431, on the invocation of responsibility for wrongful acts; and paras. 439 et seq, on the erga omnes character of some obligations implicated by climate change).