Heatwaves in southern Europe, a massive rise in sea levels, periods of drought coupled with heavy rainfall and flooding: Climate change is threatening the livelihoods of many people. In its eagerly awaited legal opinion (Obligations of States in respect of Climate Change), the International Court of Justice (ICJ), the main judicial body of the United Nations, unanimously emphasises the existential threat posed by man-made climate change and derives from this the obligation of individual states to do something about it. Accordingly, states that violate their obligations under international climate protection agreements can be held legally responsible. At the reading of the opinion in The Hague on 23 July 2025, ICJ President Yuji Iwasawa from Japan explained that such a failure by a state could constitute an act contrary to international law.

The proceedings before the ICJ caused quite a stir: many statements and comments were received there, as well as extensive oral presentations. The legal opinion was commissioned by the United Nations General Assembly back in spring 2023, when it formulated two questions for the ICJ:

1. What are the obligations of states under international law to ensure the protection of the climate and other parts of the environment from anthropogenic greenhouse gas emissions vis-à-vis states and present and future generations?
2. What are the legal consequences for states if they cause significant damage to the climate system and other parts of the environment through their actions and omissions? The second question was also explicitly aimed at special obligations towards small island developing states, which are generally considered to be particularly affected by climate change, even though they themselves only contribute to a small extent.

The Court's answers are like an all-round blow: the judges mainly deal with the various international treaties that are relevant to climate protection. These include the United Nations Framework Convention on Climate Change, the Paris Agreement and the International Bill of Human Rights. However, the ICJ also looks at international environmental law, which is shaped by customary law, as well as other agreements characterised by environmental law, in particular the Convention on Biological Diversity. In this context, the ICJ urges states to fulfil their treaty obligations.

It should be emphasised that the ICJ stresses the connection between environmental degradation and human rights: various human rights cannot be fully realised in the different regions of the world if people are not able to live in a clean, healthy and sustainable environment. In doing so, the ICJ is following the case law of other courts that have already dealt with so-called climate claims. Unfortunately, the opinion omits aspects of climate justice and future generations. This criticism is also reflected in the dissenting opinions of some of the judges.

The expert opinion is not revolutionary in its findings. It is not legally binding. Rather, it is an appeal in that it clearly calls on the international community to adhere to existing obligations and advance climate protection. As before, it is still up to the individual states themselves to implement the obligations under international law in their national legislation. Those who do not wish to do so can, in case of doubt, terminate such a treaty once it has been entered into.

At the end of their opinion, the judges point out that climate change is a highly complex and multi-layered phenomenon that entails possible responsibilities of several states over long periods of time. With regard to demands for compensation from states that emit large quantities of greenhouse gases without doing enough to combat climate change, the ICJ merely stated that this would have to be decided on a case-by-case basis. According to the opinion, these states do not necessarily have to fear any particular consequences.   

Nevertheless, the legal opinion provides argumentative support for environmental activists. It could also give new impetus to lawsuits by individual affected parties, which NGOS is strategically bringing before national courts.