Differentiation through due diligence: Common but differentiated responsibilities and respective capabilities in the ICJ’s 2025 climate advisory opinion

This article argues that the ICJ Advisory Opinion on Climate Change is the first articulate judicial application of the principle of common but differentiated responsibilities and respective capabilities (‘CBDR-RC’). Earlier judicial engagements with CBDR-RC, including by the European Court of Human Rights, the International Tribunal for the Law of the Sea (‘ITLOS’), the Inter-American Court of Human Rights and the UN Committee on the Rights of the Child, recognised the principle’s relevance without articulating its operational content. The ICJ does so in two ways. It characterises CBDR-RC as a manifestation of equity carrying a distributive function, and it ties the principle to the customary duty of due diligence to prevent significant environmental harm. By linking it to due diligence, however, the Court raises the question of the relationship between differentiation and due diligence, against a backdrop of the dilution risks flagged by the 2011 Advisory Opinion of the ITLOS Seabed Chamber and reinforced by the minimum core doctrine of international human rights law: differentiation may calibrate the standard of due diligence according to a State’s capabilities and circumstances, but it cannot reduce that standard to a point at which the underlying obligation is deprived of its protective content. The General Assembly’s follow-up resolution of 20 May 2026, which calls upon States to act with due diligence in accordance with CBDR-RC, confirms the practical significance of this reading. The result is a framework through which climate-related disputes can be argued and adjudicated without either flattening inequalities among States or allowing differentiation to become a licence for inaction.