A lot of puzzles here. China, the Philippines, and Vietnam are parties to the UN Convention on the Law of the Sea, which provides for arbitration in case of disputes under that treaty. The Philippines initiated an arbitration against China in 2013 over the Spratly Islands area. Vietnam now has signaled that it will join that arbitration. The overall goal seems to be to obtain an authoritative rebuke of China’s broad claims over the South China Sea.

China has refused to participate in the arbitration. It has not exercised its right to appoint one of the arbitrators. It declares the arbitration illegitimate. Yet it is bound to arbitrate under the treaty, and the arbitration can proceed without it, as Julian Ku explains. Sean Mirski, writing in The National Interest, argues that nonetheless China fears an adverse judgment:

Yet despite the case’s practical insignificance, China has been frantically—and unsuccessfully—trying to stop it from proceeding. In January 2014, Beijing reached new levels of desperation, and allegedly offered to withdraw its ships from Scarborough Shoal if the Philippines would delay filing its memorial in the case. While that proposal should be viewed with suspicion—after all, Beijing has reneged on deals relating to the shoal before—it is nevertheless an extraordinary offer if true: China was willing to give up control of territory over which it claims sovereignty just to avoid a bit of bad publicity. So while China won the battle for Scarborough Shoal, it may have lost the war, all because Manila was able to find something that Beijing valued even more than the territory: its reputation for complying with international law. To China, its reputation is intimately connected to its long-term growth strategy, and the country cannot afford to advertise its total non-compliance with international law.

We will see. What is odd is that China was free to opt out of compulsory jurisdiction under the UNCLOS. Unlike many other countries, it didn’t opt out when it ratified the treaty. Could it now? I assume so.

Update–It was pointed out to me that UNCLOS parties can opt out of compulsory jurisdiction only with respect to some disputes, and not disputes over EEZ boundaries, sovereignty over islands, and the other matters that are at stake in the South China Sea. China did opt out of the compulsory jurisdiction for the unrelated matters in 2006. So if it loses the arbitration, it can only disregard the judgment. It could also withdraw from UNCLOS.