The Pacific islands contribute the least to climate change. But they’re the most vulnerable to its impacts. The issue of maritime boundaries and sea level rise is current and critical for our Pacific Island neighbours, whose combined maritime areas are 44 times greater than their combined land areas.

The UN Convention on the Law of the Sea gives each island a 200-mile exclusive economic zone, normally measured from the low water line of its coast. Straight baselines connecting points on the coast or offshore features may also be used in certain circumstances.

The rights associated with their maritime zones, including rights over fisheries, are key to their continued economic development. But rising sea levels threaten to reduce the extent of coastal states’ maritime zones as coastlines retreat, or offshore features, such as islands, rocks and reefs, used as part of the baseline, are eroded or submerged.

The problem gets trickier because UNCLOS states that islands that can’t sustain human habitation or economic life of their own are “rocks” and don’t qualify for an EEZ. The surrounding ocean area becomes high seas and is available for distant water fishing nations to exploit marine resources at will. The central western Pacific accounts for over half of the world’s total global tuna catch.

Five years ago, the Marshall Islands introduced legislation on maritime limits that included essentially a geographic information system file turned into text, with hundreds of pages of co-ordinates. Other Pacific nations are mapping their remote island territories and submitting the data to the UN, hoping to secure permanent rights to their EEZs, irrespective of sea level rise. Like the Marshalls, rather than basing their EEZs on maritime charts, (which may change), they’re attempting to legislate that their EEZs be set by geographical co-ordinates.

Australia assists by supporting a Pacific maritime boundaries project, enabling Pacific island states to not only delimit their maritime boundaries with each other but update legislation, define baselines and delineate the outer limits of their maritime zones where there’s no overlapping claim with a neighbouring state. The updates are shared with the UN secretary-general, consistent with obligations under UNCLOS.

But while it’s all well and good for the island states to have a co-operative and co-ordinated approach among themselves, where they recognise these limits, the critical part is missing. There’s been no hint yet that these declared maritime claims and rights over resources within them are acceptable to everybody else. To date, there have been no test cases. The legal issues are now being examined by the International Law Commission.

But aside from legal questions, the strategic dimension of this issue is the China challenge. A recent Chatham House research report on perceptions of strategic shifts in the Indo-Pacific examined the views of the strategic policy communities in seven regional countries. As part of the research it asked “do you think UNCLOS will still be in effect in 2024?”

All states thought yes, except China. None of the Chinese respondents thought UNCLOS would be in place in the same form by then. Some thought it would be rewritten and some thought it would be obsolete and ignored.

China is now strengthening its ties with the island nations through infrastructure building and predatory lending. Now China may find another door opening. Its “magic island-making” boats that have been operating in the South China Sea are now looking for new places to dredge.

States like Kiribati and the Marshall Islands have indicated that they have, understandably enough, no interest in becoming a source of climate refugees so they propose to raise the level of their islands. The Maldives have already done this, with more artificial islands being constructed. It certainly looks like there’s an opening for China to extend a helping hand to the Pacific with their demonstrated island-making capabilities.

Given the coral reefs destroyed by Chinese island building in the South China Sea and the risks of greater economic dependence on China by Pacific nations, it’s the last thing we’d want to see happen in our neighbourhood.

Existing maritime rights should be maintained and preserved for our Pacific family, regardless of sea level rise, in the interests of stability and regional security. The extent of Australia’s own maritime jurisdiction might also be affected with sea level rise affecting the Great Barrier Reef.

Australia has been supportive of defining and declaring baselines, limits and boundaries consistent with UNCLOS. But we should now be more explicit that these limits should stay in place regardless of sea level rise.

Consistent with our Pacific Step-up there’s a real diplomatic role for Australia to play in promoting and reinforcing Pacific practice in the islands’ efforts to stabilise baselines for maritime limits and boundaries. Such an approach would be preferable to pushing for an amendment to UNCLOS or a new agreement that would carry its own political and legal risks.