CYIL vol. 11 (2020)

CYIL 11 (2020)


4. Evolution of custom as a source of international environmental law The sources of international law are set in the form of provisions under Article 38 of the Statute of the International Court of Justice and comprehend: (i) international conventions; (ii) custom; and (iii) the general principles of law. Although they do not maintain any hierarchic aspect among themselves, Ian Brownlie argues that one of the drafts of the Statute had a successively to the wording, what could betoken a primary intention to hierarchize the sources. International environmental law, albeit a self-contained, fragmented system, but eternally adhered to international law, also finds its sources under that same provision. Although apparently simplistic at first glance, it is not uncommon for one to be faced with many academic writings on the incessant search of the existentialism of certain international environmental norms. Can these norms be better defined as treaty-law, custom or as general principles of law? Right from the start, it is noted that treaty norms are easier to identify, after all, the eyes of legal scholars tend to readily trust that whichever constitutes positive law. General principles of law, on the other hand, related (or not) to the environmental field could be more thoroughly assessed, but these do not fall within the scope of the present review. Yet, one must be wary that there are strong theories sustaining the nature of the principle of sustainable development to be that of a general principle of law . 39 This section addresses the existence of custom in international environmental law, beginning with the notion of customary international law. 4.1 Customary International Law While listing the sources known to international law, Article 38 of the Statute of the International Court of Justice refers to ‘international custom, as evidence of a general practice accepted as law.’ 40 As Ian Brownlie argues, there are numerous sources of custom, depending on their relevance and the circumstances in which they are invoked. For him, national and international judicial decisions, diplomatic correspondence, the praxis of international bodies, ILC documents, among many more (or less) complex documents, may be understood as evidence of certain customs. 41 Theoretically, however, the formation of custom in international law is based on the emerging reciprocity of two fundamental elements: general practice of certain norms among sovereign states and o pinio juris sive necessitatis , or simply opinio juris . 42 As for the Conventional Theory, 43 revisited by Koskenniemi, custom originates from the symbiosis of both elements, opinio juris being represented by the psychological element (an internal aspect, which distinguishes it from pure coercion), while general state practice

39 Ibid 145. Voigt considers the sustainable development principle to be an altogether settled general principle of law. 40 Statute of the International Court of Justice (24 October 1945).

41 BROWNLIE, Ian, Principles of Public International Law (Oxford University Press 2003) 6. 42 Ibid 7. Brownlie also lists elements such as duration and consistency of the practice.

43 ‘Conventional theory attempts to construct a theory of custom between the fully descending (natural law) and the fully ascending (treaty).’ KOSKENNIEMI, Martti, From Apology to Utopia: The Structure of International Legal Argument (Cambridge University Press 2009) 410.


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