Sea levels are rising as a result of global warming. Photo: File
Legal history was made on 23 July when the International Court of Justice (ICJ) released its advisory opinion on the Obligation of States in Respect to Climate Change. At the request of the Pacific Island nation of Vanuatu, supported by more than 130 countries, the United Nations General Assembly asked the ICJ for such an opinion in 2023.
The ICJ is the UN’s main judicial body and is often referred to as the World Court. It has a dual role: first, to settle disputes between member states brought before it in accordance with international law and, second, to give advisory opinions on legal questions referred to it by duly authorised organs and bodies of the UN.
In the advisory opinion the 15 judges of the ICJ unanimously called for greater responsibility in climate protection and commented on the following questions:
- What obligations do states have under international law to ensure the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions for states and for present and future generations?
- What legal consequences arise from these obligations for states that have caused significant damage through their actions or omissions?
The judges unanimously determined that UN member states are obliged to do their utmost to slow down global warming.
I do not wish to judge whether this decision comes too early or too late, but so far it has not been possible to curb global greenhouse gas emissions, which is why the UN warned in a report last year that current climate policy would lead to warming of more than 3°C above pre-industrial levels by 2100.
The ICJ has presented a non-binding decision, the details of which certainly need to be evaluated more closely.
The ICJ is of the opinion, among other things, that climate protection agreements and customary international law impose binding obligations on the contracting states to ensure the protection of the climate system and other parts of the environment from greenhouse gas emissions caused by humans.
It is important to mention that, in examining its arguments, the ICJ relies primarily on the reports of the Intergovernmental Panel on Climate Change (IPCC), which reflect the best available scientific knowledge on the causes, nature and consequences of climate change.
The ICJ called on wealthy states to better fulfil their international obligations to curb environmental pollution, as they otherwise risk having to pay compensation to nations severely affected by climate change. It rejected arguments that governments are only bound by climate agreements such as the Paris Agreement and have no other obligations under international law. Under the Paris Agreement, more than 190 states have committed to limiting global warming to 1.5°C.
Although the court’s opinion is not binding, it carries legal and political weight in that it can at least influence future climate litigation. For example, it pointed out the possibility that large emitters could be sued more successfully in the future, which will undoubtedly be viewed critically in wealthier regions of the world.
According to the ICJ, remedial measures also include restitution — such as the reconstruction of destroyed infrastructure and the restoration of ecosystems — as well as financial compensation.
The court is of the opinion that central human rights treaties, as well as the human rights recognised under customary international law, are part of the directly relevant applicable law.
Furthermore, the court considers that the principle of sustainable development, which concerns the “need to reconcile economic development with the protection of the environment”, guides the interpretation of certain treaties and the establishment of rules of customary international law. This principle gives rise to the obligation to prevent significant environmental damage and to strive for a fairer distribution of the burdens of climate change obligations, including for future generations, taking into account the historical and current contributions of states.
So, under international law, every country must do its best to stop global warming from exceeding the 1.5°C mark.
According to the ICJ, this legal obligation arises not only from the Paris Agreement, but also from human rights, maritime law and the customary international law obligation to prevent transboundary damage.
The ICJ’s clarification advocates for greater coherence in international law, placing the protection of the climate system on the basis of stricter due diligence obligations.
The ICJ’s opinion is in line with recent statements by other international courts. These include the opinion of the Inter-American Court of Human Rights of July 2025, the opinion of the International Tribunal for the Law of the Sea, and the ruling of the European Court of Human Rights on the climate lawsuit brought by the association KlimaSeniorinnen Schweiz against Switzerland in 2024.
According to international law, the ICJ states that the human right to a clean, healthy and sustainable environment is essential for the enjoyment of other human rights. Of course, this perception could be limited by the fact that the United States, historically the world’s largest emitter of greenhouse gases, wants to reverse its climate responsibility.
In any case, the ICJ opinion is likely to change a lot in terms of the upcoming climate negotiations in Brazil in November 2025 and new climate lawsuits.
UN secretary general António Guterres already sees the ICJ opinion as a victory for the planet. According to him, states must act against fossil fuels. If they fail to prevent climate damage, they could be ordered to pay reparations.
But it will probably not be quite that simple. There are still some tough legal hurdles to overcome. In addition, the fight against climate change must be taken up by society as a whole and across all disciplines, including politics and economics, not only by international law. Nevertheless, the ICJ has elevated the discussion to another level.
Oliver C Ruppel is professor at the Faculty of Law at Stellenbosch University, where he also heads the Development and the Rule of Law Programme, which is under the Stellenbosch Climate School. Ruppel is a member of the World Commission on Environmental Law of the International Union for Conservation of Nature, which was involved in the proceedings before the International Court of Justice that concluded last week.