The master key to international law: systemic integration in climate change cases

This article is the first scholarly examination of the function of systemic integration in the climate change context. The article assesses the role that the notion of ‘systemic integration’ is playing in making climate change justiciable internationally, and traces the path along which it brought the principle to become a key notion in climate litigation. It explores the fundamental question of how pre-existing legal norms (to the Paris Agreement) have been used to address questions about climate change. Systemic integration is a principle of treaty interpretation enshrined in Article 31(3)(c) of the Vienna Convention on the Law of Treaties, which requires consideration of other rules of international law in the course of interpreting a treaty. Often operating ‘as an unarticulated major premise in the construction of treaties’, its function is nevertheless ‘analogous to that of a master-key in a large building’ (McLachlan 2005). The underlying premise is that international law is, in essence, a system. This article looks into how the principle is currently operating in practice in climate litigation and, in doing so, it draws some reflections on the wider significance of the principle for international law more generally. The article explores the systemic integration arguments considered in the Torres Strait Islanders case, the first international case on climate change to be adjudicated on its merits, which set in motion a wave of international climate cases, and considers the function of systemic integration in the pending advisory opinions before international courts.