Academic journal article Denver Journal of International Law and Policy

Multilateral Treaties and the Environment: A Case Study in the Formation of Customary International Law

Academic journal article Denver Journal of International Law and Policy

Multilateral Treaties and the Environment: A Case Study in the Formation of Customary International Law

Article excerpt


Although the question of whether multilateral treaties create customary international law upon coming into force remains controversial, there is good reason to suppose that they do.(1) Pressing global problems demand cooperative solutions, and cooperative solutions are best achieved by means of the treaty process. Yet treaties bind only those states that are parties to the treaty, and often the critical number of parties is not great enough to assure an effective international response to global problems like environmental degradation. So it is tempting to assert that multilateral treaties generate an "instant custom"(2) that obligates even non-parties to adhere to their terms.

In an earlier article in the Denver Journal of International Law and Policy we argued that multilateral treaties can in fact generate customary international law upon coming into force when three basic conditions are met:

1) A sufficient number of states in the international system accept the treaty.

2) A significant number of those states whose interests are substantially affected by the treaty (hereinafter "pertinent states") are parties to the treaty.

3) The treaty does not allow reservations on the part of the parties.(3)

We do not intend to repeat our argument here. Instead, we shall examine the universe of environmental treaties to see which treaties, if any, qualify as customary international law under our standards. We do so for two reasons. First, our prospective case study will enable us to sharpen and refine the standards themselves, thus demonstrating with some degree of precision how they structure the reach of customary international law in one particularly important policy area. Second, the study should aid a state in understanding its legal obligations to other states regarding the environment.

We will begin in Part II with a brief review of our three conditions and a discussion of why we think them necessary for the formation of customary international law. In Part III we briefly discuss some preliminary matters regarding the formation of instant custom. Then in Part IV we will arrange the existent multilateral treaties on the environment into three categories, viz., those treaties that establish customary international law according to our standards, those treaties that do not, and those troubling cases that remain too close to call from the standpoint provided by our three conditions.


The reasons for thinking that multilateral treaties establish customary international law upon coming into force derive from the principle of customary international law itself. Customary practices reach the status of international law when a large number of the states within the international system suppose these practices establish appropriate guidelines for the relations of states.(4) Presumably, a treaty relation between a large number of states could be based upon the same conviction. When this is the case, there is no need to suppose that treaty requirements must "harden" or "ripen into" customary international law.(5) The significance which a large segment of the international community attaches to the provisions of the treaty is evidenced by the treaty itself. There is, so to speak, nothing that needs to harden; things are hard enough already.

Nevertheless, one cannot decide abstractly which multilateral treaties qualify as sufficiently "hard"; this requires the establishment of some criteria capable of guiding judgment on the matter. The three conditions introduced at the outset are designed to meet this objective with some degree of specificity. As we shall see, however, these conditions contain an inescapable generality and this means that we cannot hope to achieve perfect clarity on the question of which multilateral environmental treaties actually create customary international law. …

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