Confirmation of climate protection obligations under international law and legal consequences of violations

In its opinion of 23 July 2025, the International Court of Justice clarified the existing obligations under international law to protect the climate and outlined the conceivable legal consequences of breaching them.

Background and questions to be answered

The background to this is Resolution 77/276 of 2023, in which the UN General Assembly decided to request an advisory opinion from the International Court of Justice (ICJ) on the following questions (abridged)

"(a) What are the obligations of States under international law to ensure, for the benefit of States and present and future generations, the protection of the climate system and other parts of the environment from anthropogenic greenhouse gas emissions;

b) what legal consequences arise from these obligations for states that have caused significant damage to the climate system and other parts of the environment through their action or inaction, vis-à-vis states or peoples and individuals?"

Existing obligations under international law on climate protection (question a)

In order to answer the question of what obligations states have under international law in connection with climate change, the ICJ derives the existing obligations from what it considers to be the most directly relevant bodies of law. There is no lex specialis relationship between these rules.

Firstly, the ICJ examines the obligations of states under the climate change treaties (the United Nations Framework Convention on Climate Change - UNFCCC, the Kyoto Protocol and the Paris Agreement). The obligations under the climate change treaties are determined according to the principle of common but differentiated responsibilities and capabilities and vary depending on the level of development of the respective country. Developed countries (so-called Annex I countries such as Germany) have more extensive obligations than developing countries. The level of development also has an impact on the standard of due diligence to be applied.

Irrespective of their specific categorisation, it is clear that all obligations arising from the climate protection agreements are "genuine", binding obligations. The main obligation is probably the development of and compliance with nationally determined contributions (NDCs) in accordance with Article 4 (2) of the Paris Agreement.

States generally have a margin of discretion when organising their obligations, but this is limited by the standard of due diligence, which is decisive in individual cases but strict in view of the threat posed by climate change. For the NDCs, this means that each contracting party must do everything in its power to ensure that its contributions to climate protection correspond to the highest possible ambitions.

The ICJ then explains that obligations to prevent significant damage to the climate system and other parts of the environment and to cooperate arise from customary international law. These apply even if states are not party to the climate protection treaties. Other regulations also contain similar climate protection obligations.

Consequences of violating the above obligations (question b)

In answering the question of what consequences arise from a breach of the obligations listed, the ICJ makes it clear that its opinion only outlines the general legal consequences. The specific determination of the responsibility of individual states or groups of states would be reserved for future complaints.

It is not the emission of greenhouse gases per se that is contrary to international law, but actions or omissions that cause significant damage to the climate system in violation of a state's international obligations. The consequences of a breach of duty arise from the general rules on state responsibility.

The issues of attribution and causality are problematic in the case of state responsibility in connection with climate change. The ICJ states that even in the climate context, an act or omission contrary to international law (such as the lack of regulation of private actors) can be scientifically verifiable and attributable to the state in individual cases. The question of causality is relevant in the context of reparation. There must be a causal link between the unlawful act of the state and a specific damage.

The ICJ also clarifies that the obligations of states to protect the climate are erga omnes in nature. This means that every state can assert a breach of duty by another state, irrespective of its own damage.

As conceivable legal consequences of unlawful acts, the ICJ mentions - depending on the violation and the type of damage in the specific case - the obligation to cease and desist and not to repeat the offence, as well as full reparation, including restitution, compensation and/or satisfaction.

No impact of the opinion on Germany

The ICJ opinion is unlikely to have a significant impact on German climate protection measures or national case law.

The ICJ makes it clear that obligations under international law in relation to climate change must be complied with. However, there is no obligation for states to implement specific measures. Nothing new emerges from the report in this respect. In the future, Germany will continue to have a margin of discretion in the organisation of its concrete climate protection measures, which is limited by the respective duty of care to be observed.

Even if the ICJ emphasises the erga omnes effect of climate protection obligations under international law, it is not to be expected that there will be an increase in international legal actions brought by states against other states. In the context of such lawsuits, the questions of specific breach of duty, imputability and causality will in any case take centre stage.

An increase in climate protection-related lawsuits to enforce obligations under international law is also not to be expected in the domestic context. It is true that - as is the basis of the BVerfG's climate decision (decision of 24 March 2021 - 1 BvR 2656/18) - duties to protect could be asserted under Article 2 para. 2 GG and Article 20a GG, which go beyond Article 59 para. 2 GG and Article 25 GG in conjunction with Article 20 para. 3 GG. Art. 20 para. 3 GG are "charged" under international law (see BVerfG, loc. cit., Juris para. 201). However, this does not result in a concrete, enforceable obligation for Germany to implement certain measures. The provisions of the Paris Convention were also integrated into national legislation in 2019 in accordance with Section 1 sentence 3 KSG and must also be observed in this context. Even before the ICJ report was published, it was therefore clear that Germany had to fulfil its obligations under international law in the area of climate protection. The opinion does not result in any changes to substantive law. For this reason, neither an increase in climate protection-related lawsuits nor a change in domestic case law in this regard is to be expected.

The ICJ's opinion therefore does not represent a "turning point" for Germany, but confirms obligations under international law that have already been recognised and taken into account at national level.

Source reference
International Court of Justice, Obligations of States in Respect of Climate Change, Advisory Opinion, 23 July 2025