Multilateral treaties and the environment: a case study in the formation of customary international law.

• Jurisdiction: United States
• Date: 22 March 1999
• Author: Carr, Craig L.

1. INTRODUCTION

   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.

2. MULTILATERAL TREATIES AND CUSTOMARY INTERNATIONAL LAW

   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. This problem, however, can be overcome by appeal to the obligatory nature of international law. We take it as a principle of law that its obligatory character must be clear. That is, if Treaty X creates a legal obligation, those subject to Treaty X must be able to understand that they have an obligation to obey it. If there is some question about Treaty X's status as law, there is also some question about whether it is obligatory. Where we cannot say with surety that an obligation exists, there is no such obligation. So, hard or troublesome cases, we will conclude, do not make customary international law under our conditions.

   The three conditions introduced above are relatively straightforward. For a multilateral treaty to generate customary international law upon coming into force, a sufficient number of states must accept it, a significant number of pertinent states must accept it, and it must not allow reservations.6 Perhaps the best way to make these conditions clear is to apply them to a specific area of international concern, like the environment, with a reasonable number of multilateral treaties that establish a foundation for international law. Before we turn to the more applied discussion, however, a few general remarks about our three conditions are in order.

   1. The Number of Parties to the Treaty

      The notion of customary international law derives from the general belief that the shared customary practices of numerous states provide reason to suppose that such widely accepted practices deserve to be respected as lawful.(7) They meet the criterion of general propriety since they already regulate the relations of a great many states. Presumably, the officials of those states adhering to these customary practices have found them to be appropriate regulations. The condition of general propriety can also be met, however, by numerous states accepting a particular treaty regulation. Here, too, it is possible to conclude that a large number of states--in this case the parties to the treaty--consider the regulations associated with the treaty appropriate for the governance of inter-state relations. The numerical condition, then, seems a necessary requirement for any inter-state practice to qualify as customary international law.(8)

      Nevertheless, the condition is obviously imprecise; how many states must ratify a multilateral treaty before it can be said to establish customary international law?(9) It hardly seems reasonable to think that a modest number of states should be able to bring into force a treaty that would then obligate the remaining states of the world. On the other hand, if the number of required states is too large, there is little point to thinking that multilateral treaties can generate customary international law. Few such treaties could hope to receive the general support required to establish instant custom, and the point would quickly become moot.

      Perhaps it is worth noting that the numerical condition raises problems even in more traditional areas of customary international law formation. Here, too, we need to consider how many states must adhere to a custom before it receives the general allegiance required to create international law. For its part, the International Court of Justice (ICJ) has demonstrated an inclination to measure state involvement as pertient to the formation of customary international law without any further need to identify a magic number that brings such law into being.(10) If, however, we are to use our conditions as a guide to thinking about when multilateral treaties form customary international law, we must do better than this.

      Nevertheless, the abstract assertion of a specific number is sure to seem arbitrary. Moreover, the number of states that are parties to a particular treaty may not indicate either efficacy or pertinent support. For example, at this writing only eighty-three states have ratified the Vienna Convention on the Law of Treaties (Treaty Convention).(11) Although this is a sizeable number, it remains less than half of the states of the world.(12) However, this may be less important than the fact that the world's major treaty making states (including the United States which accounts for 7% of the world's treaties) are not included in this number.(13) When it comes to the identification of a magic number demonstrating significant support for certain treaty provisions, then, the question of how many parties there are to the treaty may be less important than the question of who these parties are. If all the major treaty making states ratified the Treaty Convention, the case for thinking it establishes customary international law would presumably be greater than it now is.

   2. Pertinent States

      This point suggests that treaty ratification by certain pertinent states is a more significant determiner of instant custom than the sheer number of ratifications. We understand pertinent states to be those states whose participation in a treaty is required if the treaty is to have real meaning and a real chance of achieving its intended objective.(14) In the case of the Treaty Convention, for example, pertinent states would be the major treaty making states. Absent their involvement, it seems pointless to insist that the Treaty Convention establishes customary international law governing the treaty process.

      Another apt illustration of the pertinent state requirement is the International Convention for the Prevention of Pollution from Ships (MARPOL).(15) By 1990, parties to MARPOL accounted for 85% of gross merchant tonnage.(16) At present, however, fewer than half of the world's states have ratified MARPOL, and yet 85% of the world's significant shipping states are included among those parties.(17) The number of pertinent state parties thus looks more than sufficient to conclude that MARPOL establishes customary international law.

      The number of identifiable pertinent states will vary according to the treaty and the issue in question. Depending upon the issue, some multilateral treaties may have few pertinent state...