The Relevance of Habitability (and its Loss) for the Status of ‘Islands’

The Relevance of Habitability (and its Loss) for the Status of ‘Islands’

[Ms Frances Anggadi (Twitter: @francesanggadi) is a PhD candidate at the University of Sydney Law School, co-chair of the Oceans and International Environmental Law Interest Group of the Australian and New Zealand Society of International Law, and researcher at the University of Sydney Marine Studies Institute.  Frances’ research interests include maritime zones and sea-level rise and the importance of State practice in international law methods.]

Having the status of an ‘island’ is essential for a feature to support the full set of maritime zones under the international law of the sea. Will sea-level rise destabilise the legal status of ‘islands’, causing a loss or reduction of their maritime zones? A number of scholars have argued that the loss of an island’s capacity to sustain human habitation might have this legal effect.  For example, if sea-level rise were to taint the freshwater reservoir of an island – rendering the island uninhabitable – Caron argues that the island could no longer be relied upon to support an exclusive economic zone.  

However, a significant number of States are putting forward a different view, emphasising the potential legal stability of the status of an ‘island’ notwithstanding sea-level rise effects. Antigua and Barbuda have stated that ‘sea-level rise cannot lead to the requalification of islands as rocks’, implying that the status of an ‘island’ would be undisturbed by the effects of sea-level rise. This position also underpins the view held by members of the Pacific Islands Forum and the Alliance of Small Island States that the United Nations Convention on the Law of the Sea (UNCLOS) supports ‘maintaining maritime zones established in accordance with the Convention, and rights and entitlements that flow from them, notwithstanding climate change-related sea-level rise’ (PIF Declaration and AOSIS Leaders’ Declaration). This collective view of 39 UN Member States has received support from other States, including Germany, Japan and the United States.  

Clarifying the legal implications of habitability loss for the status of ‘islands’ is clearly important for those States already grappling with the present and projected effects of climate change.  It is also timely to focus on this issue because – unlike extensive debates about ‘ambulatory’ baselines (including on this blog) – it remains an understudied aspect of the implications of sea-level rise and international law, including within the ongoing work of the International Law Commission (ILC) on this topic generally.  

With the aim of contributing to these debates, this post argues that if an island has lost its capacity to sustain human habitation, destabilisation of ‘island’ status should not be taken as a fait accompli. This is because such a conclusion rests upon a contested interpretation of Article 121 of UNCLOS.  By connecting debates on the interpretation of Article 121 in the context of the Philippines v China arbitration with scholarship on the legal effects of sea-level rise, it can be seen that an alternative conclusion about the legal implications of habitability loss is not only possible, but preferable.  And by fully accounting for State practice relating to Article 121, it becomes clear that the factual risks of habitability loss need not lead either logically or legally to the full loss of maritime zones.

Habitability and Maritime Entitlement

Article 121 – the sole provision in the ‘Regime of Islands’ in UNCLOS – is central to the differential allocation of maritime entitlements in relation to different geographic features. An ‘island’, defined as ‘a naturally formed area of land, surrounded by water, which is above water at high tide’ (Article 121(1)) has the same entitlement to a territorial sea, contiguous zone, exclusive economic zone (EEZ) and continental shelf as other land territory (Article 121(2)). An exception to this is that ‘[r]ocks which cannot sustain human habitation or economic life of their own shall have no exclusive economic zone or continental shelf’ (Article 121(3)).   Conclusions about the legal effect of habitability loss on ‘island’ status must rest upon an interpretation of the requirement in Article 121(3).

Sea-level rise can cause saltwater intrusion and interact with other climate change effects, such as more frequent and intense storms and storm surges, and other extreme weather events (IPCC’s Sixth Assessment Report and Special Report on the Ocean and the Cryosphere).  Storlazzi predicts that islands with no other source of freshwater ‘will be ‘uninhabitable by the middle of the 21st century— not by the end of the 21st century or the middle of the 22nd century as previously suggested’.  Sea-level rise and other climate change effects raise a wide range of practical issues for the life of a community (Nations of Water), such as how to maintain adequate food security in the face of changing ocean conditions affecting the health and availability of fish, as well as raising important social and cultural considerations, such as whether sacred burial grounds may need to be relocated from traditional coastal locations (Views adopted by the Human Rights Committee). Some or all of these factors may contribute to a loss of insular habitability as a matter of fact, a phenomenon that has immediate humanitarian dimensions and in the most extreme cases, raises the prospect of community dislocation (already experienced by some communities, such as in Papua New Guinea and Fiji).

But how do these factual risks of habitability loss relate to the legal requirements of Article 121(3)? Some scholars suggest a straightforward approach to this legal question: that once habitability is lost, the requirement in Article 121(3) is no longer satisfied, resulting in a loss of entitlement to an EEZ and continental shelf (Caron, Rayfuse).  Murphy ascribes a causal connection between loss of habitability, change of legal status, and loss of maritime zones, arguing that if an island becomes uninhabitable, ‘an island that is not a “rock” within the meaning of the LOS Convention Article 121, paragraph 3, might become such a rock.  If so, then the rock would no longer support either an exclusive economic zone or a continental shelf’ (Murphy, see also Rothwell).

A Two-part Model of Features Under Article 121: The Tribunal’s Approach in Philippines v China

Figure 1.

Underpinning these scholars’ conclusions is the same interpretation of Article 121 as that adopted by the Tribunal in Philippines v China: ‘[d]oes the feature in its natural form have the capability of sustaining human habitation or an economic life? If not, it is a rock’ ([483]).  For the Tribunal, capacity to sustain human habitation or economic life (HHEL) is a necessary precondition for a feature to qualify as a ‘fully entitled island’ ([494]).  

This interpretation may be usefully viewed as a two-part model of the regime of islands under Article 121 (Figure 1), under which capacity to sustain HHEL is what differentiates a high tide feature that is entitled to all maritime zones (an island) from a high tide feature that is only entitled to a territorial sea and contiguous zone (a rock).  Under this two-part model, capacity to sustain HHEL functions as the sole fulcrum for the maritime entitlement of all naturally-formed high tide features; its presence or absence determines which of the two categories of legal status applies. 

A Three-part Model of Features Under Article 121: A Critique on the Basis of State Practice

The Tribunal’s approach to the interpretation of Article 121 has attracted strong criticism on the basis that it insufficiently accounts for State practice.  While the Tribunal recognised the potential relevance of State practice, it did not consider evidence of such practice and concluded that ‘as far as the case before it is concerned, there is no evidence for an agreement based upon State practice on the interpretation of Article 121(3) which differs from the interpretation of the Tribunal’ ([553]).  However, since the Award, numerous scholars have identified many examples of State practice in which coastal States have claimed an EEZ and/or continental shelf on the basis of features that do not conform with the Tribunal’s requirements for full maritime zone entitlement (Judge Guillaume, Song, Tanaka, Oude Elferink, Talmon (‘Article 121’ in Proelß), Mossop, Klein, Norquist and Phalen, Churchill (‘Rocks’ in MPEIL)).  

For example, Tanaka writes that it would be difficult to see how Jan Mayen (around which Norway has proclaimed a 200-nm fishery zone and continental shelf) would satisfy the Tribunal’s test since the feature has no stable population and the people working on Jan Mayen are entirely dependent on external resources.  Similarly, while New Zealand has proclaimed an EEZ and continental shelf around the tiny Bounty Islands (around 1.35km2), Mossop queries whether they too would meet the Tribunal’s test for full maritime zone entitlement, being without vegetation, fresh water or extractive activity of any kind.

Figure 2.

This evidence suggests that ‘there is an abyss between the tribunal’s approach and the practice of many States’ (Oude Elferink). Talmon explains that what emerges from State practice is an interpretation of Article 121 in which ‘there are three categories of islands: (1) rocks that cannot sustain human habitation or economic life of their own; (2) rocks that can sustain human habitation or economic life of their own; and (3) all other islands.  Only the first category of islands does not have an EEZ or continental shelf’ (‘Article 121’ in Proelß). Consistent with State practice, this three-part model of the regime of islands (Figure 2) gives a restrictive application to the exception in Article 121(3) by applying the requirement for HHEL only to those islands which are rocks, not to all islands. So while the two-part model solely relies on capacity to sustain HHEL as the precondition for entitlement to full maritime zones, the three-part model suggested by State practice gives capacity to sustain HHEL a second-order role, applying only to rocks.  Islands which are not rocks are covered by the general rule (Article 121(1) and (2)), and do not attract the exceptional requirement in Article 121(3).  

Whether a two- or three- part model is adopted in relation to the interpretation of Article 121 has significant implications for debates about the legal effects of habitability loss on ‘island’ status.  If the capacity to sustain HHEL is not required to qualify for status as an ‘island’ in the first place, then the loss of such capacity to sustain HHEL should have no relevance to such status.  Rather, loss of capacity to sustain HHEL might only logically affect the maritime entitlement of a rock. A potential difficulty might be that a State will seldom expressly articulate whether it is proclaiming full maritime zones because it considers the feature to be an ‘island’ within the meaning of Article 121(1), or because it considers the feature to be a rock capable of sustaining HHEL.  But the many instances of coastal States establishing full maritime zones in circumstances that are unlikely to satisfy the HHEL test strongly suggest the former approach, favouring a generous interpretation of ‘island’ and a narrow interpretation of ‘rock’.  If this is the case, then loss of capacity to sustain HHEL is only likely to affect a very small number of features, if any at all. 

Avoiding Path Dependency: The Potential Irrelevance of Habitability for the Status of an Island (Which is not a Rock)

Interpreting Article 121 as a two-part model of features creates a logical path dependency: because HHEL is needed as a precondition for status as an ‘island’, absence of HHEL calls that status into question.   However, there is a major gap between this model as articulated in the Philippines v China and extensive State practice.  So far, following the Award, States have not revisited established maritime zones that deviate from the Tribunal’s approach; nor has the Tribunal’s reasoning been marshalled in protests or challenges between States.  Neither have international courts and tribunals had occasion to affirm the Tribunal’s findings on the interpretation of Article 121.  Against this backdrop, the Tribunal’s interpretation of Article 121 – including the two-part model of features underpinning it – remains fragile (Tanaka).

These difficulties with the two-part model must be taken into account when considering the potential implications of sea-level rise for legal status and maritime entitlement.  Not only is the interpretation of Article 121 contested, but State practice illuminates a different interpretative path, along which the factual risks of habitability loss need not logically lead to the loss of full maritime zones.  Under the three-part model suggested by State practice, capacity to sustain HHEL is an exceptional requirement that pertains only to the maritime zone entitlements of rocks, not all islands.  This understanding – coupled with the likelihood that few States will proclaim an EEZ and/or continental shelf for rocks capable of sustaining HHEL – means that the status of many features as ‘islands’ might be unaffected by habitability loss.  


In its upcoming seventy-fourth session, the ILC’s Study Group on sea-level rise will once again be focussing on the law of the sea aspects of its mandate (2022 ILC Report).  The ILC has previously noted ‘the potential significant consequences of being reclassified as a rock due to sea-level rise, possibly becoming a rock that “cannot sustain human habitation or economic life of their own” ’ (2021 ILC Report). However, it is not apparent whether it has yet had the opportunity to focus closely on the underlying interpretative debates on the legal significance of habitability for ‘island’ status under Article 121. On this issue, the ILC may find it useful to have regard to the many examples of State practice supporting a three-part model of features under Article 121, under which habitability is a precondition for the extended maritime entitlement of islands which are rocks, but not all islands.  

Notwithstanding the decision of the Arbitral Tribunal in Philippines v China, it is open to the ILC to consider that this approach is more consistent with promoting the legal stability of maritime zones, an objective which is being given increasing prominence by States (Anggadi, Vidas and Freestone). In this light, the stability of ‘island’ status should be seen as a dimension of such legal stability (Anggadi).  Furthermore, both State practice and States’ pronouncements on the importance of legal stability should be evaluated as a matter of interpretation, relevant to the requirements of Article 31(3)(b) of the Vienna Convention on the Law of Treaties.  If this interpretative path is taken, States facing the factual prospect of the loss or degradation of island habitability need not fear that it will also result in the loss of their maritime jurisdiction.  

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Environmental Law, Featured, General, Law of the Sea
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