Following the Permanent Court of Arbitration’s (PCA) unanimous ruling undermining the legal basis for China’s “nine-dash line” claim, Beijing repeated its prior threat to establish an aircraft defense identification zone (ADIZ) above the South China Sea (SCS). An ADIZ is an area of airspace, adjacent to but beyond the national airspace and territory of the state, where aircraft are identified, monitored, and controlled in the interest of national security.

Presumably the purpose of a South China Sea ADIZ would be to reinforce China’s territorial claims – a tangible rejoinder to the PCA’s award and international criticism. In November 2014, Beijing established an ADIZ over the East China Sea (“ECS ADIZ”) encompassing disputed maritime territory. The ADIZ could also serve as a means of excluding and deterring U.S. freedom of navigation operations, which include military flights designed to challenge excessive claims to maritime jurisdiction. China has developed a series of landing strips on reclaimed land in the contested Spratly archipelago that could be used to enforce the ADIZ.

However, a Chinese ADIZ above the South China Sea, in addition to aggravating tensions, would be misguided as a matter of international law and mistaken as a matter of policy. ADIZs are creatures of customary international law, the implementation of which are conditioned by principles derived from the inherent right of self-defense and treaties such as the Convention on International Civil Aviation (Chicago Convention) and United Nations Convention on the Law of the Sea (UNCLOS). Although more than 20 states, including the United States, have established ADIZs, these limited defensive zones have not been used for the greater lawfare ends potentially envisioned by Beijing. An examination of the fundamental elements of ADIZs, reveals the folly of such an approach.

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First, the role of ADIZs is to provide a means of anticipatory self-defense from incoming and immediate threats emanating above the high seas. The ADIZ is a modern variant and extension of the “cannon-shot” rule, which provided for a buffer zone in coastal waters based on the reach of littoral defenses. During the Cold War, the United States established the first ADIZs as a means of protecting the homeland from the inbound threat posed by long-range Soviet bombers. Employing an ADIZ to aggrandize disputed maritime claims would deviate from state practice and encroach upon the rights of all states in the high seas. In this scenario, the legal rationale of ADIZs would be essentially reversed from defensive to offensive, from the protection of national sovereignty to the coercive extension of sovereignty.

http://thediplomat.com/2016/09/south-china-sea-the-case-against-an-adiz/