(The Hague, Netherlands, Wednesday 23 July 2025) Today the world’s highest court, the International Court of Justice (ICJ), has handed down a highly-anticipated advisory opinion, defining a crucial moment in international climate law. The opinion clarifies that states must take decisive action under international law to prevent climate change, limiting global warming to 1.5°C, or risk future legal action.

The ruling follows an initiative spearheaded by the small island state of Vanuatu, supported by powerful campaigning from Pacific Island states and youth activists, which resulted in the ICJ being asked to clarify what major polluting countries’ obligations are under international law. These groups are among the most vulnerable to the escalating impacts of climate change, from rising sea levels threatening small island nations to the long-term consequences for future generations. 

The ICJ has established clear legal duties that will have far-reaching consequences for global climate action at national, regional and global law and policy levels. The court made clear that states must take all measures available to reduce greenhouse gas (GHG) emissions in line with the 1.5°C warming goal. Crucially, the court clarified that states party to the Paris Agreement must submit progressively more ambitious Nationally Determined Contributions (NDCs) at the highest possible level of ambition for any given state, and that the NDCs, taken together, must be capable of achieving the necessary GHG emissions reductions. Countries must then “make best efforts” to achieve their NDCs.

However, the court also confirmed that the international climate agreements, including the United Nations Framework Convention on Climate Change (UNFCCC) and the Paris Agreement, are not the only sources of international law which determine the legal duties of states to limit GHG emissions. Customary international law and human rights law, among others, were just as relevant. In practice, states which are not party to the climate agreements will likely still need to demonstrate a level of climate ambition that is equivalent to that required by those agreements in order to comply with their obligations under international law.

Finally, the court confirmed that states which fall short of their international legal obligations and fail to prevent significant harm to the climate can be held responsible for internationally wrongful acts under international law. This may expose states to significant liabilities, including ceasing any wrongful acts, making assurances of non-repetition, and making full reparation for the harm caused to other states.

This advisory opinion forms a vital body of landmark international rulings on climate change: the ITLOS advisory opinion on ocean pollution, the Inter-American Court of Human Rights opinion on human rights, and now the ICJ’s opinion. Together, these rulings bring clarity to international legal obligations at the highest level. The ICJ, having the widest mandate of the three tribunals, has addressed state obligations under the broad spectrum of international law, completing the legal jigsaw and sending an unequivocal message: states, particularly historic and major emitters, have clearly defined duties to mitigate climate change, and there are serious consequences for harm caused to the climate, the environment, and other states.

With this transformative ruling, the Court provides an essential roadmap for governments, courts, and civil society worldwide to ensure accountability and climate justice.

Opportunity Green’s Legal Officer, Olivia Moyle says:

"This landmark opinion is a triumph for international climate justice. The Pacific Island nations – among the most vulnerable to climate change – have emerged as powerful leaders at the forefront of international legal development.  The ICJ has now affirmed what these climate vulnerable countries have long demanded: that all countries, and in particular major emitters, must act decisively to prevent further harm. Crucially, this includes regulating fossil-fuel based activities and the conduct of private companies, as primary drivers of the climate crisis. Today’s opinion makes clear that even the most powerful polluters must comply with international law. This moment belongs to the Pacific, and to all frontline communities fighting for their future."

Opportunity Green’s Legal Officer, Dominika Leitane says:

“For too long, major emitters could hide behind the lack of clarity on climate change-related obligations in international law. States carrying the lion’s share of responsibility for greenhouse gas emissions could defer to the allegedly discretionary nature of Nationally Determined Contributions (NDCs) under the Paris Agreement to justify a lack of climate action. Others yet could avoid responsibility by refusing to engage with the international climate regime at all. Corporations continue their polluting operations, assuming that international law only concerns states, not private entities. The ICJ’s landmark advisory opinion puts an end to this era of unaccountability: it makes clear that NDCs must be ambitious, that states outside of the Paris Agreement are still bound to reduce GHG emissions in line with customary international law, and that states must regulate the conduct of private actors to prevent harm to our climate. This is truly the start of a new era of climate accountability.”

Ends

Notes to editors

Opportunity Green is an NGO working to unlock the opportunities from tackling climate change using law, economics, and policy. We do this by amplifying diverse voices, forging ambitious collaborations and using legal innovation to motivate decision makers and achieve climate justice, with particular emphasis on the aviation and shipping industries.

Last year, Opportunity Green joined over 110 countries and organisations in putting forward a submission to the Court. The NGO’s submission urged the Court to consider international shipping and aviation emissions in its opinion. It also called on the Court to clarify the legal obligations of states under international law with respect to the mitigation of emissions from these two sectors. This is of utmost importance because these two highly-polluting sectors together account for almost 5% of global emissions, and are both projected to grow significantly. And yet, these sectors remain weakly regulated: the emissions reduction targets set by their global regulators, the International Maritime Organization (IMO) and the International Civil Aviation Authority (ICAO), are insufficient to meet the Paris Agreement’s 1.5°C temperature goal.

Opportunity Green will be assessing the results of the advisory opinion in detail and will be issuing more in-depth analysis once our legal team has had the opportunity to review and digest the advisory opinion in full.