EDO legal analysis: International Court of Justice advisory opinion on obligations of states in respect of climate change
On 24 July 2025, the International Court of Justice (ICJ) issued a landmark advisory opinion regarding the obligations of states to address climate change under international law.
As the highest court in the world, the role of the ICJ is to hear disputes between states, usually around international law, and to clarify questions of law asked by the United Nations via production of an advisory opinion.
The ICJ’s recent opinion follows two other significant advisory opinions from the International Tribunal for the Law of the Sea (ITLOS) and the Inter-American Court of Human Rights (IACtHR).
Together, the three opinions comprehensively analyse a broad body of international law and determine that States must work urgently to mitigate climate change.
What is an advisory opinion?
Advisory opinions are not binding on states and do not automatically result in punishments or relief to those harmed in the same way that a typical court judgment would.
Instead, advisory opinions clarify how the law is to be understood and followed, interrogating what is considered lawful under international law, different treaties and principles.
The three opinions each clarify if and how different treaties should be interpreted on the matter of climate change, each determining that states have an obligation to reduce greenhouse gas (GHG) emissions.
What does the ICJ opinion say?
At the request of the United Nations General Assembly, initiated by the Pacific Island nation of Vanuatu and supported by over 130 countries, the ICJ provided an advisory opinion that determines the obligations of states in relation to climate change under international law generally.
The ICJ found unanimously that states must reduce their GHG emissions under international law and minimise any actions that would result in their release.
What action is required by states, including Australia, according to the ICJ?
The ICJ clarified what actions are necessary for a state to take to counteract climate change.
It found that it is inconsistent with the obligations above to continue supporting, licensing, and approving fossil fuel production.
GHG emissions arising from fossil fuels must be reduced, both in terms of fossil fuel production and consumption, irrespective of where the fuel is burned. Importantly, production of fossil fuel was found to be an “internationally wrongful act”.
Fossil fuel exporting states, including Australia, remain accountable for the totality of GHG emissions from these produced fossil fuels, even if they are shipped to and burned in another State.
Notably, the ICJ rejected the arguments of many major emitting states (including made by Australia) that the only source for legal obligations were international treaties explicitly related to climate change, such as the Paris Agreement or the United Nations Framework Convention on Climate Change.
Rather, the ICJ found that obligations to reduce GHG emissions can arise from any international agreement, including treaties related to human rights and general environmental protection.
Considering this broad body of international law, the ICJ found that states are obliged to address their GHG emissions under requirements of due diligence and prevention principles to guard against human rights breaches and significant harm to the environment, both on land and at sea.
It was found that these instruments all imparted a duty for states to act, even if they are no longer a party to the Paris Agreement.
What if states fail to reduce emissions?
States, including Australia, that fail to reduce GHG emissions in accordance with the obligations set out above, could be taken to the ICJ.
The likely targets of these actions will be the world’s major polluters and fossil fuel exporters, such as the United States, China, India, and Australia.
This liability could include being ordered by the ICJ to reduce their GHG emissions, in line with minimum global targets, and enact measures to restore the environment, insofar as this is feasible.
The ICJ may also order these states to compensate, financially or otherwise, other states, such as Pacific Island states or individuals that have been disproportionately harmed by the impacts of climate change.
What does the ITLOS opinion say?
In advisory opinion C31, released on 21 May 2024, ITLOS responds to a request to identify the obligations under the United Nations Convention on the Law of the Sea (which Australia is a party to) for States to address climate change.
ITLOS determined there is an obligation to prevent and mitigate GHG emissions to ensure the protection of marine environments.
ITLOS found that GHG emissions constitute marine pollution and thus there is a legal obligation for states to act with due diligence to prevent or mitigate harm to the marine environment.
The extent of the obligation is determined by the best available science and a State’s resources but ultimately requires states to take all necessary measures to eliminate or reduce GHG emissions which could damage the marine environment.
What does the IACtHR opinion say?
On 3 July 2025, the IACtHR advisory opinion AO-32/25 responded to requests to clarify states’ obligations to address climate change under the American Convention on Human Rights. It was found that states must act to reduce GHG emissions to prevent human rights breaches.
The most significant aspect of this decision was the clarification of the right to a healthy environment.
This was found to extend to individuals, those impacted immediately by environmental harm, and the collective, which considers current and future generations’ continuing right to enjoy a healthy environment.
The IACtHR also found that this right applies to nature itself, meaning there is a duty to protect the environment even where people appear unaffected, given that all life necessarily depends on a healthy environment.
Finally, they found that this right is a Jus Cogens or peremptory norm, meaning it cannot be ignored or disregarded by a State for any reason.
While Australia is not a party to the American Convention on Human Rights and the decision relates to rights and duties under American Convention on Human Rights, the IACtHR is key regional international court.
Its decisions and opinions significantly inform international law and are regularly referred to by the ICJ, ITLOS and Australia’s own domestic courts.
Why do these three advisory opinions matter?
Though these advisory opinions are not binding on countries, they will still have global, far-reaching influence.
Together these three opinions each represent a meaningful step toward strengthening legal accountability, safeguarding the environment, and protecting fundamental human rights threatened by climate change.
The opinions will support work around the globe seeking to hold governments to account, whether through court actions or advocacy to strengthen laws, to ensure stronger action to reduce GHG emissions to mitigate climate change.
Together these three opinions underscore the urgency needed for State action to implement measures to prevent further emissions and apply pressure on governments to respond to the global climate emergency.
