Trustees of humanity: From juridical metaphor to legal concept

Abstract The International Court of Justice's 2025 Advisory Opinion on Obligations of States in Respect of Climate Change deploys the phrase ‘trustees of humanity’ in the context of intergenerational equity, offering a striking convergence with the theory of sovereignty advanced in my Sovereigns as Trustees of Humanity (2013). This essay examines the relationship between the two. It argues that the Opinion supports the earlier theory in several important respects—rejecting purely domestic conceptions of sovereign responsibility, affirming sovereignty's embedment in a broader normative order, and requiring other‐regarding conduct—while also developing it in ways unforeseen by the earlier account. The essay also argues that the trusteeship framework resolves a question the Opinion leaves open: When do States' obligations with respect to greenhouse gas emissions arise? Finally, the essay reflects on the Opinion's possible significance for the evolving grammar of sovereignty in light of contemporary geopolitical challenges.