Sea Level Rise, Maritime Sovereignty in the Pacific, and Implications for the South China Sea

Mirco Di Giacomo | Pacific Fellow

Sea level rise (SLR), a phenomenon associated with climate change, is often understood as an existential threat to many archipelagic nations, every day closer to being submerged into oblivion.


While SLR most certainly presents an existential threat, in the most immediate future it poses primarily a challenge to the sovereignty of many of these insular nations, most located in the Pacific.


The sovereignty challenge derives from the way maritime borders and zones are measured; in most cases, under the United Nations Convention on the Law of the Sea, the measurement extends from the baseline, a point broadly corresponding with the coastline. As such, loss of coastline translates to an effective recession of the baseline and thus loss of territorial waters, and shrinkage of current Exclusive Economic Zones (EEZ). This threat to maritime sovereignty is especially concerning in light of the scarce mitigation tools available to affected countries. While the existential threat (submersion) can be mitigated through re-claiming lost land and even expanding the reclamation beyond current coastlines, artificial land has no bearing over territorial waters or EEZ claims.


Many Pacific nations are particularly low-lying: Tuvalu’s average elevation is merely 2 meters. Australia and New Zealand (the two largest Pacific nations) have external territories with elevations just as low. Even more significantly, for countries consisting mostly of relatively small islands (archipelagic nations), their maritime EEZ is often many times larger than their total land. In other words, loss of coastline can mean loss of most of these state’ territories.


Unsurprisingly, insular nations, already facing pressures from receding coastlines, are taking action. On August 6, the Pacific Islands Forum Members declared their coastlines are not and will not be affected by SLR, and will remain unvaried. They made it clear they “do not intend to review and update the baselines and outer limits of [their] maritime zones as a consequence of climate change-related sea-level rise”, as these nations interpret the United Nations Convention on the Law of the Sea as having no obligations to “review nor to update charts or lists of geographical coordinates once deposited”, and therefore not accounting for SLR.


The strong standpoint taken by the Pacific Islands Forum is understandable, as is their anxiety on the matter. The view of the international community is not conclusive on the matter, meaning their maritime borders might indeed be shrinking. In 2007, the International Court of Justice (ICJ) ruled in favour of contemporary geographical features taking precedent over historically-agreed borders when deliberating a maritime border dispute between Nicaragua and Honduras. Honduras took a non-geographic uti possidetis juris stance (the legal principle positing new states ‘inherit’ the borders agreed by the previous sovereignty holder), but the ICJ supported contemporary geographical features having precedent over historical arrangements. As such, it is understandable countries facing coastal recession are beginning to ‘feel the squeeze’ in regards to their borders. If borders are reduced, they may find foreign fleets taking resources or fishing in what used to be their EEZ. This would not be without precedent — Chinese fishing fleets are currently operating within other countries’ EEZ in the South China Sea, as China does not recognise these other EEZs as legitimate (although admittedly for reasons other than SLR).


From this sovereignty tension, however, a strategic potential might follow, going beyond mere mutual support between Pacific Islands Forum members, or other similarly affected bodies. The most significant among the possible strategic potentials is likely to involve China, which may likely advocate for a ‘fixed’ border interpretation over one supporting the review of borders in light of SLR or other phenomena.


China’s interest here would rise from its claim over a number of extremely low-lying islands in the South China Sea that now face threat of SLR. China is also likely to support claims of sovereignty over reclaimed land, not implausible given that many of its claimed semi-submerged islands in the South China Sea have been artificially expanded and risen. Potentially, this could push many Pacific nations away from their traditional ally, the United States, and cause tension between Australia, New Zealand, and the U.S., should the U.S. advocate for a stance supportive of moving maritime borders and if this ‘shotgun marriage’ to preserve maritime sovereignty with China proves more convenient. And while Australia and New Zealand may only lose some external territories, this is not the case for archipelagic nations facing far larger loss of territorial waters and EEZs, thus making the stakes for them particularly high.


Alternatively, SLR might also provide a not-at-fault opt-out option for China from the South China Sea — should in the future the diplomatic, economic and/or military costs of assertively claiming sovereignty over South China Sea islands prove not worth it, China will have the option to cease claims disputes without handing sovereignty to another country nor contradicting previous claims, instead merely asserting there is nothing to be claimed anymore.


SLR is posing a sovereignty challenge for many nations, especially archipelagic ones. This challenge is increasingly immediate, and international courts and intergovernmental bodies will need to determine how maritime zones and borders are delineated. This process will be extremely political and involve high stakes, and require strong diplomatic work by many countries. From these stakes there will be deriving strategic opportunities likely to, at least temporarily, shift existing strategic arrangements.



Mirco Di Giacomo is the Pacific Fellow for Young Australians in International Affairs.