Treaties and Determination of Customary International Law by Courts and Tribunals: Are There Limits to the Use of Methodological Shortcuts?
by Xuexia Liao (Peking University Law School)
Published on 16 November 2022
The significance of treaties for the identification of customary international law is well recognised and the modes of interaction between treaty and customary international law clearly formulated, notably in the 1986 Nicaragua case and in Conclusion 11 of the International Law Commission’s (ILC) Conclusions on Identification of Customary International Law. Nevertheless, a recurring theme that fully reveals the difficulties of ‘understand[ing] customary international law in all its complexity’ (Jörg Kammerhofer & Panos Merkouris in the introductory blog post) is that, in practice, international courts and tribunals exclusively or primarily rely on the texts of the treaties not just as a starting point of assessing the customary process, but as a methodological shortcut in the identification procedure. This theme is discussed in the book The Theory, Practice, and Interpretation of Customary International Law and by earlier scholarly works (see here and here). The use of shortcuts is common, which, in the words of Vladyslav Lanovoy, ‘circumvent[s] the practical difficulties that may arise in demonstrating the two elements of custom.’
It may be understandable that any court or tribunal tasked to identify the existence or content of a customary international rule cannot possibly scrutinise practice or opinio juris of all the States in the world. Yet, the problem is the unconstrained use of such methodological shortcuts. Frequent or excessive reliance on written texts (including treaties not in force and UNGA resolutions) can lead to far-reaching consequences beyond the dispute under consideration. For example, what has been said by the International Court of Justice (ICJ) may be cross-referenced by other courts or tribunals as an authoritative statement on the customary status of certain rules, which ‘often are just short of a self-fulfilling prophecy of [customary international law]’, as observed by Lanovoy, as well as by Mariana Clara de Andrade in relation to the World Trade Organization’s Appellate Body.
In addition, the ICJ’s declaration that certain treaty provisions have customary status so as to apply them to non-States parties particularly illuminates why over-reliance on treaty texts is methodologically weak and, in the long run, normatively problematic. A most curious instance in the recent jurisprudence of the ICJ is the declaration that Article 121(3) of the United Nations Convention on the Law of the Sea (UNCLOS) is part of customary international law. That provision provides that ‘rocks which cannot sustain human habitation or economic life of their own shall have no exclusive economic zone or continental shelf.’ In the 2012 Nicaragua v. Colombia judgment, the ICJ, without offering any evidence of State practice or opinio juris, observed that ‘the legal régime of islands set out in UNCLOS Article 121 forms an indivisible régime, all of which (as Colombia and Nicaragua recognize) has the status of customary international law’ (para. 139).
This observation suggests that, to the ICJ, mere textual and logical links between treaty provisions are sufficient to conclude that all provisions under the same article form part of customary international law. The reference that the parties to a dispute recognise a rule to have customary status is also methodologically objectionable. It also contradicts the Court’s own jurisprudence. As the ICJ itself emphasised in the 1986 Nicaragua case, ‘[t]he mere fact that States declare their recognition of certain rules is not sufficient for the Court to consider these as being part of customary international law.’
More importantly, without distinguishing whether the treaty codifies, crystallises, or generates customary international law, the ICJ may have embarked on a separate path to normativity which does not have a corresponding reality embedded in State practice, and it is in this aspect that the declaration of customary status of Article 121(3) is most problematic. A cursory look at State practice is sufficient to realise that coastal States tend to claim the continental shelf and the exclusive economic zone (EEZ) even on the basis of miniscule maritime features (see Gilbert Guillaume). In fact, maritime claims in respect of uninhabited islands that are unlikely to be capable of sustaining human habitation may well be recognised in bilateral maritime boundary agreements, such as in the delimitation agreement between Australia and France with respect to Heard and McDonald Islands, and Kerguelen Island respectively. It is difficult to ascertain whether and how State practice distinguishes rocks from fully-fledged islands. It is extremely rare that coastal States give up their claims to the continental shelf or the EEZ. In this respect, the United Kingdom’s practice in relation to Rockall was exceptional.
The practice of some non-States parties to UNCLOS also points to the recognition of claims to the continental shelf and the EEZ from very minor maritime features. For instance, Venezuela’s claim to the EEZ around the tiny sandy cay known as Aves Island was recognised in its bilateral delimitation agreements with the Netherlands, United States and France. The Venezuela-France agreement was concluded with awareness of Article 121(3) being incorporated into the final draft of UNCLOS and entered into force after the conclusion of UNCLOS. The finding that Article 121(3) constitutes customary international law may therefore have unwarranted normative effect for non-States parties to UNCLOS. Although UNCLOS has acquired the status of a quasi-universal treaty, some States, including the United States, Turkey and Syria, deliberately choose to stay outside the treaty regime. The presumption of UNCLOS being a point of departure to ascertain customary international law is a rebuttable one, and should remain nonetheless anchored in general practice involving both States parties and non-States parties alike.
These implications indicate the limits of using treaties as methodological shortcuts in decision concerning the identification of customary international law. The ILC’s Conclusions on Identification of Customary International Law provide practical guides and helpful reference in this respect. As cautioned by the ILC, and by the ICJ itself in North Sea Continental Shelf, a treaty-inspired customary process is not lightly to be regarded as having occurred. In addition to those well-established conditions that underlie the customary process, a critical point stressed by the ILC Commentaries is that ‘in and of themselves, treaties cannot create a rule of customary international law or conclusively attest to its existence or content’ (Conclusion 11).
That said, perhaps more relevant for a court or tribunal is a weighing exercise between the practical need of settling disputes and the thoroughness of judicial reasoning. Looking back at Nicaragua v. Colombia, one wonders whether the findings on the customary status of Article 121(3) served any practical use, since the ICJ anyway refrained from judging the status of the disputed maritime features between the two parties against that provision. The wisdom of avoiding saying anything unless necessary may well be virtue rather than vice, especially because a court or tribunal’s decision on the existence or content of customary international law may, in the words of Lanovoy, have ‘an immeasurable impact on developing, or conversely, arresting “processes of growth without which the law will be atrophied”.’
Xuexia Liao is Assistant Professor at Peking University Law School