Is the NPT Customary International Law?: A Question Central to the Marshall Islands ICJ Case

I was just reading Avner Cohen’s recent piece on the Marshall Islands case over at the BAS website. In it Cohen writes:

The lawsuit reflects a growing belief among international legal and policy experts (as well as some diplomats) that the time has come for the NPT to be treated—due to its near universal adherence—as part of customary international law by which all states must abide, regardless of whether or not they actually signed the treaty.

Based on this reasoning, the Marshall Islands asks the International Court of Justice to rule that all nine nuclear states are in material breach of their legal obligation to disarm under international law, regardless of their status under the NPT. Currently the international community does not consider the NPT to be part of international customary law; if it were, the treaty would have a legal status similar to that of the international bans on slavery or torture. Should the International Court of Justice make such a ruling, it could elevate the discourse on nuclear disarmament from vague declarations of intentions to stark statements of legally binding commitment.

Cohen is certainly right to identify the question of whether the NPT, or at least Article VI of the NPT, is part of customary international law, as a central question in the Marshall Islands (RMI) case. It is the argument on which the entirety of the RMI’s case against those of the nine potential respondents who are not parties to the NPT, rests. But I thought I would try to provide some clarity to Cohen’s discussion of this question.

The question of whether the NPT, in whole or in part, has entered into customary law is one that has been knocking around in international legal discourse for a long time. I’ve talked with colleagues at conferences about the subject for many years, though as far as I know there has not yet been a focused treatment published on this question. I know some people over the years have told me they were working on one, but I have yet to see it in print. If there is such a treatment out there, I would be happy to have attention drawn to it in the comments.

Generally speaking, broadly-subscribed-to treaties, such as the NPT, are fertile ground for potentially finding that a process sometimes referred to as parallel customary law creation has occurred. This simply means that, even if the principles codified in the treaty were not, prior to codification, a part of customary international law, the very fact of their codification, and even more importantly the subsequent implementation of these principles by states parties, under the (quite correct) impression that these principles are legally obligatory upon them, satisfies the two elements of state practice and opinio juris that together turn a principle into a rule of customary international law.

This phenomenon is quite common in the international legal system. Examples include principles of the 1977 Additional Protocols to the Geneva Conventions on the Law of Armed Conflict, principles of the 1969 Vienna Convention on the Law of Treaties, and principles of the 1982 UN Law of the Sea Convention. In each of these contexts, states who are not parties to the treaties themselves, have recognized that, while the treaty per se is not binding on them, some of the principles codified in the treaty have, through parallel state practice and opinio juris, become rules of customary international law which are binding on them through that separate source of international law.

These examples are also illustrative of another characteristic of parallel customary law, which is that customary law development parallel to a treaty is not an all-or-nothing proposition. In each of the examples cited above, it is only some of the principles codified in the treaty that are considered to have entered into the corpus of customary international law. Not necessarily all of them. This is why, for example, the ICRC’s study on customary law in the law of armed conflict is so important – it is a rigorous analysis of which of the principles codified in the Geneva Conventions and their Additional Protocols have entered into CIL. And that study found that the substance and definitions of the obligations as between the treaty and CIL differs significantly.

So let’s now come back to the NPT. In my 2009 book I wrote that the NPT had not, at least in toto, entered into customary international law, unlike the CWC and the BWC:

On a normative development level as well, the contract treaty nature of the NPT has not given the elements of customary law creation clear universal principles to attach to, in order to enable the creation of parallel custom, unlike in the cases of the Chemical Weapons Convention (CWC) and the Biological Weapons Convention (BWC), to be discussed in detail below. Such parallel customary law in the cases of these other multilateral nonproliferation treaties constitutes an important supplemental source of legal obligation through which even non-parties, and particularly secondary proliferators of WMD technologies, may be bound to the terms of the cornerstone international legal instruments.

I still think that this analysis is correct. However, there are some articles of the NPT that are worded in such a way as to comprise universal obligations upon all states parties to the treaty, notwithstanding they are a part of the treaty’s quid pro quo structure of obligations. The most important of these are Articles IV & VI of the treaty.

As I’ve already explained, there is no problem legally with having individual articles or provisions of a treaty pass into customary international law, even if the entirety of the treaty in which they are found does not. So the question I think becomes, is there sufficient evidence of state practice and opinio juris to support the conclusion that either or both Article IV or Article VI have become principles of customary international law?

Focusing on Article VI, as that is the operative provision in the Marshall Islands case, this basically becomes an empirical question. The tests for state practice and opinio juris are well expressed and defined in international legal sources, and what is needed is a focused study evaluating state practice, and inferences about the sense of legal obligation under which states have taken that action, in order to answer the question of whether the principles in Article VI have indeed been established as customary law. If they have been, then this hugely strengthens the RMI’s case against the four non-NPT parties in the cases.

As I said above, I have not personally conducted such an empirical study. I don’t know if anyone has. If they have, I would invite them to come forward and enlighten us!

But I will give my own sense, which is admittedly anecdotal and qualitative at this point, just from viewing the landscape of state practice and opinio juris on this question through statements made at NPT PrepComs and RevCons, etc. for some time now.

I would conclude that there are indeed a sufficient number of states who consider the obligation in Article VI of the NPT to be a binding legal obligation, and who have acted in conformity with that opinio juris, over a sufficient amount of time, with sufficient consistency, in order to establish the Article VI obligation as an obligation of customary international law, in addition to its codification in the NPT.

It must be remembered that perfect universal conformity with a rule, or recognition of the rule as binding, is not necessary for customary law to form. As the ICJ itself said in the 1986 Nicaragua case:

It is not to be expected that in the practice of States the application of the rules in question should have been perfect, in the sense that States should have refrained, with complete consistency, from the use of force or from intervention in each other’s internal affairs….the Court deems it sufficient that the conduct of States should, in general, be consistent with such rules, and that instances of State conduct inconsistent with a given rule should generally have been treated as breaches of that rule, not as indications of the recognition of a new rule.

So the fact that there are among the NWS especially, states that do not view the Article VI obligation to in fact be a binding legal obligation, does not per se mean that it is not a binding obligation, nor that it has not entered into customary law. Looking to statements of the Non-Aligned Movement, which represents a supermajority of states, as well as to the 2010 NPT Review Conference Final Document, as I did in some detail in my 2011 book, I think there is ample evidence of opinio juris to support the conclusion that the Article VI obligation is a part of customary international law, even if the NPT in its entirety is not.

This is obviously going to be a highly contentious part of the RMI’s case, particularly against India and Pakistan, who as I wrote previously are two of the only three states (along with the UK) over whom the ICJ likely does have jurisdiction to proceed with this case.