I. INTRODUCTION

The much anticipated  ICJ  Advisory Opinion of 23 July 2025 was historic in its affirmation of Member State obligations to act to curb climate change through adaptation and mitigation measures. This blog offers a rights-based perspective on one aspect of the Opinion, namely the obligation of due diligence.

II. DUE DILIGENCE IN INTERNATIONAL LAW

International law recognises a number of principles of responsibility, among them the due diligence principle which applies across many areas of international law and it is now considered part of custom.

The Court confirmed that under customary international law, due diligence imposes an obligation of conduct not just result. Responsibility is incurred not only where the desired result is not achieved, but also where the state fails to take all measures which were within its power to prevent significant harm.  Thus, a state that does not exercise due diligence in the performance of its primary obligation to prevent significant harm to the environment, including to the climate system, commits an internationally wrongful act entailing responsibility (para 409).

III. HUMAN RIGHTS DUE DILIGENCE

In light of the factors identified by the Court as relevant to the application of the due diligence principle – such as the nature of the obligation and the seriousness and irreversible nature of the harm – coupled with the stringency of the standard itself (para 246), it is noteworthy that the Court did not extend its analysis to human rights obligations. This is all the more significant in light of the Court’s acknowledgment that the degradation of the climate system and of other parts of the environment impairs the enjoyment of a range of rights protected by human rights law. (para 375).

A logical next step to connect these elements would have been to extend the obligation to exercise due diligence in the climate context to states’ primary obligation to prevent significant harm to human rights. This would have strengthened the ruling and promoted greater coherence in in relation to due diligence and international responsibility.

Indeed, the fact that the Court stopped short of recognising a free-standing right to a clean, healthy and sustainable environment militates in favour of a more expansive and explicit definition of due diligence that would encompass impacts on the enjoyment of human rights.

Such an extension would also have confirmed the potential relevance of human rights due diligence in the context of climate change more generally, particularly given the Court’s emphasis on the obligation of states to regulate the activities of private actors (para 457), but also in informing the definition of states’ human rights obligations in the context of climate mitigation and adaptation. Such an approach would promote evaluating state conduct against applicable obligations and in reliance on established methodologies and tools, such as human rights impact assessments (HRIA). Indeed, among the failures of customary law due diligence obligations, the Court cited the failure to undertake environmental impact assessments (para 444): a natural addition could have been the failure to undertake HRIA.

A key objective of due diligence should be to assess whether the probability that the object or result set by a primary rule or international obligation will not be attained (Ollino; 101). This appears central to the Court’s general analysis of due diligence, but reveals a gap in regard to human rights obligations.  This also appears to be a missed opportunity in terms of international policy coherence and a signaling of the equal relevance of climate impacts on people and the environment.

The Court’s own analysis would suggest that human rights law is relevant to the current context and should therefore be part of due diligence to assess whether States’ actions or omissions with respect to climate change would result in a breach of an international human rights obligation.

IV. CONCLUSION

The Court’s opinion represents unassailable progress.  Nevertheless, explicit guidance on human rights due diligence in the context of climate change would have been welcome and further strengthened the Opinion.

*DISCLAIMER* This blog expresses the personal views of the author and should not be attributed to the EU FRA.