Playing Fast and Loose with Article 31(3)(c) VCLT: Lessons on Systemic Integration from the ITLOS Climate Change Opinion

Abstract Systemic integration as a means of treaty interpretation in international law is receiving increasing attention in both scholarship and jurisprudence. Most recently, it featured prominently in the much-anticipated Advisory Opinion of the International Tribunal for the Law of the Sea (ITLOS) on climate change. This article analyses the Tribunal’s approach to systemic integration under Article 31(3)(c) of the Vienna Convention on the Law of Treaties, its potential consequences, and the lessons that may be drawn therefrom. It characterises the Tribunal’s approach as both expansive, in the sense that it stretches to breaking point certain elements of the Vienna Convention rules, and selective, in the sense that it does so exclusively in relation to international environmental law despite calls from participants in the proceedings to engage with international human rights standards. Each of these facets of the Tribunal’s application of Article 31(3)(c) are explored and critiqued in detail. The article concludes with a call for greater clarity and transparency in the application of systemic integration by international courts and tribunals.