International Court of Justice Sets Out States’ Climate Obligations - Major Implications for Ecocide Law
Summary
In a landmark advisory opinion, the International Court of Justice (ICJ) has clarified that states have binding legal obligations under international law not only to protect the climate system and the environment, but also to prevent harm, cooperate across borders, and provide reparations where damage occurs.
Requested by the UN General Assembly in 2023, the advisory opinion is the result of a campaign initiated by a Pacific youth movement and carried forward diplomatically by the Pacific Island nation of Vanuatu and co-sponsored and supported by over 130 countries.
Key legal obligations confirmed by the Court include:
Due diligence: "A State is . . . obliged to use all the means at its disposal in order to avoid activities which take place in its territory, or in any area under its jurisdiction, causing significant damage to the environment of another State" (para. 132, p. 48) and "the standard of due diligence for preventing significant harm to the climate system is stringent" (para. 138, p. 50)
Common but differentiated responsibilities: "The principle of common but differentiated responsibilities and respective capabilities reflects the need to distribute equitably the burdens of the obligations in respect of climate change, taking into account, inter alia, States' historical and current contributions to cumulative GHG emissions, and their different current capabilities and national circumstances" (para. 148, p. 52)
Human Rights: "The Court thus concludes that, under international law, the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights" (para. 393, p. 114)
Cooperation: "The duty of States to co-operate for the protection of the environment forms part of customary international law" (para. 142, p. 51)
Accountability: "A responsible State is under an obligation to make full reparation for the damage caused by the internationally wrongful act" (para. 450, p. 128) and legal consequences include "a) cessation of the wrongful actions or omissions, if they are continuing; b) providing assurances and guarantees of non-repetition of wrongful actions or omissions, if circumstances so require; and c) full reparation to injured States" (para. 457(4), p. 132)
By affirming that failure to prevent serious climate harm may breach international law, the Advisory Opinion reinforces the case for recognising ecocide as an international crime and makes a significant contribution to the body of jurisprudence establishing environmental protection not merely as just policy, but a legal obligation grounded in existing international frameworks.
The strongest calls to uphold and strengthen international law are increasingly coming from those most vulnerable to its erosion. In September 2024, Vanuatu, one of the world’s most climate-threatened nations, also led a coalition of states including Samoa and Fiji in submitting a formal proposal to amend the Rome Statute of the International Criminal Court to include ecocide as a fifth core international crime.
Jojo Mehta, CEO and Co-Founder, Stop Ecocide International, said:
"This Advisory Opinion is a legal watershed. It confirms that wilful environmental destruction is not just reckless. It is unlawful.
“By affirming that states have clear legal duties to prevent such harms, the ICJ has strengthened the foundations for accountability, not only reinforcing state responsibility in international law but also providing a critical legal basis that supports holding individuals personally liable for serious environmental destruction under evolving international criminal law frameworks.
“While the ICJ itself adjudicates disputes between states rather than individuals, its advisory opinion shapes the normative and jurisprudential landscape that underpins efforts to criminalise ecocide and pursue individual accountability, at national and international levels.”
“In this context, ecocide law, which seeks to criminalise large-scale environmental harm, emerges not simply as the next legal frontier but as a necessary evolution in the landscape of international justice.”
Read the full ICJ Advisory Opinion here.