Customary International Law and the Environment

This chapter highlights how, despite the large number of environmental agreements at all levels, the role of customary international law remains key in practice. First, many treaties in force remain largely unimplemented. Secondly, treaties only bind those states parties to them, and that introduces sometimes important variations in the scope of environmental agreements. Thirdly, there is at present no treaty formulating binding overarching principles interweaving sectorial environmental agreements. As a result, it is often necessary to revert to customary norms when difficulties of interpretation or implementation arise. Fourthly, custom is important to mediate between a range of environmental and non-environmental interests governed by different treaties. Finally, custom plays an important role in disputes concerning a disputed area or where there is no applicable treaty. The chapter then analyses the process of custom formation with reference to environmental norms in order to show both the ‘banality’ and the peculiarities of this process. It also looks at the content of customary international environmental law as recognized in the case law.