On July 23, 2025, the International Court of Justice (ICJ) in The Hague issued the long-awaited advisory opinion concerning the obligations of states in the field of climate change. This is a groundbreaking decision because the court confirmed for the first time, that all States have binding legal obligations to protect the climate system and combat climate change, and that the breach of these obligations constitutes an internationally wrongful act which gives rise to State responsibility.

The request for an advisory opinion was made by the UN General Assembly on 29 March 2023, with significant support from vulnerable States such as Vanuatu. The ICJ’s opinion follows on from previous advisory opinions by the International Tribunal for the Law of the Sea (ITLOS) and the Inter-American Court of Human Rights, adding to the growing body of international law in this area. In preparing its opinion, the ICJ took into account extensive written and oral submissions from States and international organisations, including the WHO and the EU, and also met with scientists from the Intergovernmental Panel on Climate Change (IPCC).

Obligations of States under international law

The Court has clearly identified the scope of States’ obligations to protect the climate system from anthropogenic greenhouse gas (GHG) emissions across various areas of international law. The most important sources of these obligations include:

• The United Nations Framework Convention on Climate Change (UNFCCC), the Kyoto Protocol and the Paris Agreement: These treaties complement each other and set binding obligations for states to mitigate GHG emissions, adapt to climate change and cooperate [195, 268, 526(a), 526(c)]. A key aspect of the Paris Agreement is goal of limiting the increase in global average temperature to 1.5°C above pre-industrial levels [27, 299, 527(f)]. The Nationally Determined Contributions (NDCs) that countries submit are binding obligations to act; they must represent progress and reflect the highest possible ambition of the country [28, 241-245, 309, 313, 527(f)]. Their preparation and implementation require due diligence, which is strict in the context of the severity of the climate threat.
• Customary international law: Even states that are not parties to climate agreements are bound by customary international law. These include: obligation to prevent significant environmental damage a obligation to cooperate The duty to prevent harm also requires due diligence, including regulation of the activities of private entities, including the cumulative effects of GHG emissions.
• International human rights law: The Court confirmed that environmental protection is a prerequisite for the full enjoyment of human rights. Climate change adversely affects the right to life, health, an adequate standard of living, privacy and the rights of vulnerable groupsThe ICJ recognized the right to a clean, healthy and sustainable environment as a human right, which is an integral part of the exercise of other human rights.
• Law of the Sea (UNCLOS): Anthropogenic GHG emissions are considered pollution of the marine environment and are therefore subject to the provisions of UNCLOS on the protection of the marine environment. The obligations also include strict due diligence. With regard to rising sea levels, the court stated that states are not obliged to update their original maritime baselines.
• Guiding principles: In the interpretation and application of these commitments, key principles are sustainable development, common but differentiated responsibilities and respective capabilities (CBDR-RC), equity, intergenerational justice and the precautionary approach. The polluter pays principle does not apply directly to relations between states in this context.

Legal consequences of breach of obligations

A breach of any of the above obligations constitutes an internationally wrongful act that gives rise to State responsibility. The Court clarified that the rules on State responsibility under customary international law also apply in the context of climate change, and climate agreements do not exclude their application as special law.

Given the nature of climate change, which results from cumulative emissions from many states, the court confirmed that the rules on state liability are nevertheless applicable. Liability can be attributed to a state for its own actions or inactions, including its failure to properly regulate the activities of private entities, such as fossil fuel production, licensing or subsidies.

For compensation of damages it is necessary sufficiently direct and certain causal relationship between the wrongful act of a State and the damage suffered. The ICJ opinion allows any State, including small island States, to hold another State responsible for a breach of these obligations, because obligations to protect the climate system are duties erga omnes (i.e. towards the entire international community) or all parties (to all parties to the contract).

The legal consequences of unlawful acts include: obligation to stop unlawful conduct, non-repetition guarantees a full compensation for damages, which may take the form of restitution, compensation or satisfaction.

Observation and potential consequences

Although the ICJ advisory opinion is not legally binding, it is expected to serve as authoritative guidance for states and the international community. The opinion is likely to influence domestic policies of states, force them to regulate GHG emissions more strictly, including for private actors, and strengthen arguments in legal disputes based on human rights and the environment.

The ICJ stressed that while law plays an important role, addressing the existential threat of climate change also requires human will and wisdom to change our habits and lifestyles to ensure a sustainable future for current and future generations. It is as if international law has laid out a map to a safer future, but navigating it depends on the collective courage and determination of the entire crew of the planet. Spring