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

Abstract

This article argues that the ICJ Advisory Opinion on Climate Change is the first substantial judicial articulation 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 advances the analysis in two related respects: 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. The Court also states that CBDR‐RC does not itself establish new obligations. That formulation leaves unresolved the tension ‐ identified by Judge Xue ‐ between equity's interpretive operation and its capacity to generate substantive norms. The due diligence analysis gives CBDR‐RC immediate operative effect within the Court's framework, without foreclosing the possibility that the principle may have freestanding substantive consequences. Differentiation may calibrate the standard of due diligence according to a State's contributions, capabilities and national circumstances, but it cannot reduce that standard to a point at which the underlying obligation is deprived of its protective content. The reasoning of the ITLOS Seabed Disputes Chamber and the minimum‐core doctrine of international human rights law support a minimum protective floor. 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.