Low-lying Pacific island nations such as Tuvalu and Kiribati face an urgent challenge as rising sea levels threaten not only their physical landmass but also the legal foundations of their statehood. Central to this issue is the question of whether maritime boundaries, which define countries’ territorial seas and exclusive economic zones (EEZs), should adjust with shifting coastlines or remain fixed despite environmental changes.
Current international law, under the 1982 United Nations Convention on the Law of the Sea (Unclos), bases maritime boundaries on coastal baselines determined by the low-water line of land features. These boundaries confer sovereign rights over resources such as fisheries and offshore minerals within a designated range—12 nautical miles for territorial seas and up to 200 nautical miles for EEZs. However, sea level rise threatens to erode these baselines, potentially reducing or eliminating the maritime entitlements of vulnerable island states.
Experts highlight that the land features generating these maritime zones must be capable of sustaining human habitation or economic life to qualify for full maritime rights. Rising seas that undermine freshwater supplies or cause submergence may change the classification of these features, thereby affecting the extent of the maritime entitlements. Chen Yitong, an international law scholar at the Ocean University of China, pointed out that such changes should not retroactively invalidate maritime boundaries that are already established through treaties or recognized legal mechanisms.
Donald Rothwell, professor of international law at the Australian National University, noted that under customary state practice, baselines are generally “ambulatory”—they can shift with changing coastlines. However, this principle complicates the situation for island states confronting climate change, as it could lead to a loss of territory and maritime rights due to natural environmental shifts, a scenario many view as inequitable.
Pacific island nations have argued that their baselines and maritime boundaries should be preserved permanently, regardless of physical changes caused by climate change. The International Law Commission has recently recommended that states should not be obligated to revise their baseline submissions to the United Nations even if coastlines recede. This emerging legal consensus aims to protect vulnerable states from losing critical maritime zones as sea levels rise.
In response, some analysts advocate for China to take an active role as both a legal advocate and technical partner for Pacific island countries. By providing maritime surveying expertise, coastal protection technology, and support for baseline documentation, Beijing could assist these nations in maintaining their maritime rights while also advancing its strategic interests in the region. China’s claims in the South China Sea—which overlap with those of Brunei, Malaysia, the Philippines, and Vietnam—are partly grounded in extensive assertions of sovereignty over islands and surrounding waters, making China’s position on maritime boundary stability especially significant.
Chinese officials have emphasized the importance of incorporating “historic rights” in discussions of maritime entitlements affected by sea-level rise. However, this approach has raised concerns among other countries due to its association with China’s expansive claims in the South China Sea. At the same time, Beijing has pledged infrastructure upgrades and disaster early-warning systems to mitigate climate impacts and support coastal restoration efforts.
Legal experts agree that addressing the implications of rising seas on maritime boundaries involves not only interpreting existing international law but also potentially developing new frameworks tailored to climate-related challenges. Some Pacific island states have already begun seeking immediate guarantees of their continued sovereignty, as in the case of the 2024 Falepili Union Treaty between Tuvalu and Australia, which recognizes Tuvalu’s statehood and maritime rights even in scenarios of submersion and facilitates migration options.
Ultimately, experts emphasize the importance of transparent, demand-driven cooperation led by the Pacific island countries themselves. Ensuring these nations’ participation in shaping legal responses and securing technical support is considered essential to upholding their sovereign rights amid environmental changes. The issue remains a complex intersection of climate science, international law, and geopolitical interests, with global implications beyond the Pacific region.