ABSTRACT
While being a significant source of international legal obligations between States generally, customary international law fulfils a less significant role in international environmental law. This is because customary rules generally take time to evolve and rarely fulfil the specific requirements of international environmental law. It is widely accepted that two main elements are required to be present in the establishment of any particular rule of customary international law. These are, first, the physical element as evidenced by a general and consistent pattern of State practice and secondly, the psychological element of acceptance by these States that such practice is either required or allowed by law, the so-called criterion of opinio juris. The presence of these two elements, of State practice and opinio juris, is sufficient to prove the existence of a binding rule of customary international law.
