To no one’s surprise, the Permanent Court of Arbitration (PCA) in The Hague has upheld all the key arguments of the Philippines in its case against China on the application of the United Nations Convention on the Law of the Sea ^[1] (UNCLOS) in the South China Sea. In its ruling, which employed even tougher language than most expected, the tribunal cut the legal heart out of China’s claim that the sea is, in effect, a Chinese lake.

The PCA ruled that China’s ‘nine-dash line,’ a 1940s-era delineation that implies ownership by China of 80% of the South China Sea, is legally meaningless. It also made clear that China’s recent land-reclamation activity, turning submerged or otherwise uninhabitable reefs into artificial islands with airstrips or other facilities, confers no new rights to the surrounding waters or any authority to exclude others from sailing or flying nearby.

Official Chinese statements on the nine-dash line have never stated precisely what it is intended to encompass. Some refer to ‘historic rights,’ others to ‘traditional Chinese fishing grounds,’ while still others suggest that it is merely shorthand for describing all the land features in the South China Sea over which China claims sovereignty. But every variation has provoked others in the region, by signaling China’s willingness to encroach on perceived fishing rights (as with Indonesia), rights to exploit resources (as with Vietnam), or their own rights to the land-features in question

The PCA’s decision punctures any notion that international law now recognizes ‘traditional’ or ‘historic’ maritime claims not directly associated with recognized sovereign ownership of relevant types of land. Recognized ownership of a habitable island, as with mainland territory, includes a 12-nautical-mile territorial sea, a 200-nautical-mile exclusive economic zone or EEZ and rights over any associated continental shelf (subject to any overlapping rights of others).

Recognized ownership of an uninhabitable rock or permanently protruding reef includes the surrounding 12-nautical-mile territorial sea. Nothing more. Without land, a state cannot claim rights to the sea.

China can and will continue to claim that, despite competing claims by Vietnam, the Philippines, and others to the land features in question, it is the sovereign owner of habitable islands and permanently protruding rocks or reefs in the Spratly and Paracel Island groups and elsewhere. In making its case, it can invoke accepted legal criteria like effective occupation or acquiescence. When added to its own coastal entitlements, China might well end up with a sizeable and entirely defensible set of rights in the South China Sea.

But the PCA addressed none of these underlying sovereignty issues in the Philippines case. And, crucially, even if all of China’s sovereignty claims in the South China Sea were one day accepted—whether through negotiation, arbitration, or adjudication—the total area, including territorial sea, EEZs, and continental-shelf rights, would still not approach the size of the vast zone encompassed by the nine-dash line.

The PCA’s decision also rules out China’s claim to an unlimited right to pursue and stare down any close surveillance of its massive reclamation activity and construction of military-grade airstrips, supply platforms, communications facilities, and in some cases gun emplacements. Such construction has occurred on seven previously unoccupied locations in the Spratlys: Mischief Reef, Subi Reef, Gaven Reef, and Hughes Reef (all previously submerged at high tide), and Johnson South Reef, Cuarteron Reef, and Fiery Cross Reef (all previously part-exposed at high tide, but uninhabitable).

Under UNCLOS, states may construct artificial islands and installations within their own EEZs, and also on the high seas (but only for peaceful purposes). In neither case can this have the legal effect of turning a previously submerged reef into a ‘rock’ (which might allow a 12-mile territorial sea to be claimed), or an uninhabitable rock into an ‘island’ (which might allow for a 200-mile EEZ as well). The Philippines case confirmed these basic principles.

In doing so, the PCA also made clear that China had no right whatsoever—at least in the case of the previously submerged Mischief Reef—to engage in any construction activity, as the territory it claims is within the Philippines’ EEZ.

China seems unlikely to abandon occupancy of any island, reef, or rock where it currently has a toehold, or to stop insisting on its sovereign ownership of most of the South China Sea’s land features. But everyone with an interest in ensuring regional stability should encourage China to take several steps that would not cause it to lose face.

These steps include a halt to overtly military construction on its seven new artificial islands in the Spratlys; not starting any new reclamation activity on contested features like the Scarborough Shoal; ceasing to refer to the ‘nine-dash line’ as anything other than a rough guide to the land features over which it continues to claim sovereignty; submitting these claims at least to genuine give-and-take negotiation, and preferably to arbitration or adjudication; advancing negotiations with ASEAN on a code of conduct for all parties in the South China Sea; and an end to dividing and destabilizing ASEAN by putting pressure on its weakest links, Cambodia and Laos, on this issue.

The alternative course, already being promoted by hotheads in the People’s Liberation Army, is to take a dramatically harder line by, say, renouncing UNCLOS altogether and declaring an Air Defense Identification Zone (ADIZ) over most of the South China Sea. Declaring an ADIZ, which the United States would certainly ignore, would sharply increase the likelihood of military incidents, with wholly unforeseeable consequences.

Walking away from UNCLOS would also be wrongheaded. China would still be effectively bound by its terms, now almost universally recognized as customary international law, irrespective of who adheres to it. The gesture of defiance would damage both its reputation and other territorial interests, not least its claims against Japan in the East China Sea, which rely on UNCLOS’s continental-shelf provisions.

If China takes a hardline path, or fails to moderate its behavior significantly in the months ahead, the case for further international pushback by countries like mine ^[2]—including freedom-of-navigation voyages within 12 nautical miles of Mischief Reef and other artificial islands in that category—will become compelling. But right now it is in everyone’s interest to give China some space to adjust course and to reduce, rather than escalate, regional tensions.