On 23rd July 2025 the International Court of Justice (ICJ) entered an Advisory Opinion at the request of the United Nations General Assembly on various questions regarding climate change and the challenges this phenomenon had to present and future generations. This was pre-empted by numerous resolutions of the General Assembly regarding measures for protection of the environment including the UN Charter, the Universal Declaration of Human Rights and numerous covenants, protocols, declarations and the relevant principles and obligations imposed on States under international customary law. At the same time the General Assembly applying the UN framework convention on climate change and the Paris agreement provided that the advice required should reflect
“Equity and the principle of common but differentiated responsibilities and capabilities in the light of different mutual circumstances.”
The General Assembly noted with alarm the extent of greenhouse gases, the particular vulnerability of developing countries, especially the least developing countries and small island developing states. Such states experience persistent drought and extreme weather events, land loss and degradation, sea level rises, coastal erosion, ocean acidification and retreat of mountain glaciers. All these factors threaten food security, water availability, livelihoods and frustrate efforts to eradicate poverty and promote sustainable development.
The ICJ decided it had jurisdiction to give an opinion on these matters because it was stating existing law. The court also considered the relevant United Nations’ resolutions, conferences, and scientific evidence affecting deterioration of the human environment, e.g., water pollution, erosion and soil deterioration, waste, noise, and the effects of biocides. On reading the scientific studies the ICJ noted that the report of the Intergovernmental Panel on Climate Change (IPCC) stated that there was “a rapidly closing window of opportunity to secure a liveable and sustainable future for all.” More importantly the IPCC added that
“the choices and actions implemented between 2020 and 2030 quote will have impact now and for thousands of years.”
Given the urgent and alarming conclusions of the IPCC the questions for the ICJ were: (a) What were the obligations of States under international law to ensure protection of the climate system and other parts of the environment from anthropogenic emissions of greenhouse gases for States and for present and future generations? And (b) what are the legal consequences under these obligations for states where they, by their emissions, have caused significant harm to the climate system and other parts of the environment with respect to: (i) States, including in particular, small island developing states, which due to their geographical circumstances and level of development are injured or specially affected by, or are particularly vulnerable to, the adverse effects of climate change? (ii) Peoples and individuals of present and future generations affected by the adverse effects of climate change? The second question (b) concerned treaty obligations not as in the first question which concerned the general rules of States’ responsibilities.
Obligations of States Under International Law
As to Question (a) the ICJ considered the applicable law, the obligations of States which were subject to the climate change treaty framework, obligations under customary international law, and other relevant international treaties. They considered obligations under relevant environmental treaties, and international human rights law. The ICJ concluded from its considerations of these matters that the three climate change treaties: United Nations Framework Convention on Climate Change and Climate, Peace and Security (UNFCCC) the Kyoto Protocol and the Paris Agreement most relevant applicable law. The United Nations Convention on the Law of the Sea (UNCLOS) was also directly relevant. Under international customary law the ICJ concluded that States have a duty to prevent significant environmental harm which applies to climate change. It also concluded that the duty to co-operate for the protection of the environment formed part of customary international law. It recognised the applicability of core human rights treaties and human rights recognised under customary international law. The ICJ considered sustainable development, common but differentiated responsibilities and respective capabilities, equity, intergenerational equity, the precautionary approach and the principle that the polluter pays all.
In terms of a non-treaty party to a climate change treaty the ICJ decided that despite being a non-party a State which does not co-operate and fulfil its customary law obligations has the burden of demonstrating that its policies and practises are in conformity with its customary international law obligations. States must also not only comply with their obligations under the climate change treaties, but also comply with their obligations under the other environmental treaties such as the Ozone Layer Convention, the Montreal Convention and the Biodiversity Convention and Desertification Convention. Again, the ICJ opined that States must take their obligations under UNCLOS into account when implementing other climate change treaties. Regarding sea level rises the ICJ concluded that States have an obligation to co-operate with other states to achieve Equitable solutions regarding the rights of affected States and their populations. Under Article 18 Vienna Convention on the Law of Treaties, states have an obligation not to act in a manner inconsistent with its object and purpose as defined in the Convention. On the human rights point, the ICJ opined that states must take their obligations under international human rights law into account when implementing the obligations under the climate change treaties as well as other environmental treaties and customary international law.
On Question (b) as to the legal consequences of States the consequences for states the ICJ concluded that responsibility for breaches of obligations under the climate change treaties and resulting loss and damage associated with the adverse effects of climate change was to be determined by the rules on State Responsibility under customary international law. In terms of responsibility the rules on State Responsibility enable a means for determining responsibility of states for climate change consequences. Questions of liability and apportionment of responsibility are to be resolved as a matter on a case-by-case basis.
In such cases causation may be a complex issue requiring scientific evidence as to whether the climate event or trend can be attributed to the anthropogenic climate change and to what extent damage caused by climate change can be attributed to a particular state or group of state actors. If there are several causes of the damage then the court must examine each cause, difficult, but not necessarily impossible. They suggest merely establishing the causal link between the event and the damage. Here the court can make an opinion with an in concerto approach in considering the weight of the evidence. Just how this works out in practise is difficult to imagine. Identification of the proportion of risk to the eventual outcome attributable to each particular event of climate change may be difficult to definitively extablish.
Diverse faces in breach then the state is obliged to cease the action and not to repeat it. Other legal consequences follow in terms of requiring payment of reparations, restitution, financial compensation by way of damages and or some declaration in satisfaction name D an expression by the court of a formal declaration as to the wrongfulness of the states conduct. In each case the court will have to determine the extent of the damage to life and property in the context of the circumstances of the case.
Unprecedented opinion
This case is unique insofar as it is unlike any other case referred to the ICJ in its history. It was given a challenging task to give an opinion within its jurisdiction in the context of the international legal order. The problem of climate change and its consequences is a much greater problem than can be encompassed within this Advisory Opinion although the Advisory Opinion is a useful tool in giving guidance for cases on the environment and climate change, for example, cases in the European Court of Human Rights. The question is much deeper and wider as it is vital to the existence of humanity. The question as the ICJ inferred is of concern politically, scientifically, economically and medically. It challenges climatologists. This is not simply a question for a group of nations who happen to be concerned with climate change it must be considered an urgent problem for all humanity. It is a question as the United Nations Framework Convention on Climate Change and Climate, Peace and Security has declared and as stated above “a matter of a rapidly closing window of opportunity to secure a liveable and sustainable future for all.”
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