Three days ago China’s Ministry of National Defense established an Air Defense Identification Zone (“ADIZ”) for the East China Sea. According to the announcement, foreign aircraft operating within the ADIZ will be subject to a couple of requirements: First, they must provide Chinese authorities with various means of identification, including by reporting flight plans, maintaining two-way radio communications and responding in a timely manner to inquiries, displaying clear marks of nationality, and maintaining the operation of any secondary radar transponders. Second, the aircraft must “follow the instructions” of Chinese authorities. If any aircraft fails to provide identification or follow instructions, “China’s armed forces will adopt defensive emergency measures.” The ADIZ is outlined in red in the map on the left and, most notably, includes the air territory above the contested Senkaku / Diaoyu Islands. Japan has warned that the ADIZ creates a risk of “unpredictable events,” while Secretary of State John Kerry and Secretary of Defense Chuck Hagel said that they are “deeply concerned” about China’s announcement and committed to defending Japan. The obvious purpose of the ADIZ is to further whittle away at Japan’s de facto control over the Islands. In this post, I want to raise two brief points on the legality of this measure.
First, the lawfulness of the ADIZ hinges in part on one’s preexisting view about sovereignty over the Senkaku / Diaoyu Islands. If sovereignty belongs to China, then it is unproblematic for the ADIZ to encompass the Islands. But if title belongs to Japan, the ADIZ is plainly unlawful. These conclusions follow from the powers that accompany sovereignty as a matter of longstanding custom. Simply put, states lack authority to regulate foreign aircraft flying over another state’s territory. While I recognize room for disagreement, I personally think that Japan has a stronger claim to sovereignty for reasons I’ve explained elsewhere. From this view it follows naturally that the ADIZ is unlawful because it effectively denies Japan’s right to fly aircraft freely over part of its own territory.
Second, even if China has sovereignty over the Islands, it does not automatically follow that the ADIZ is lawful. To understand why, it’s important first to realize that the UN Convention on the Law of the Sea establishes a system under which the sovereign powers of coastal states diminish as the distance from land increases. Sovereignty is most robust within the territorial sea, which extends 12 miles from the coastline; somewhat less extensive within a so-called “contiguous zone,” which extends an additional 12 miles out from the edge of the territorial sea; and even more limited within an “exclusive economic zone” (“EEZ”) that reaches from the outer edge of the contiguous zone up to 200 miles from the shoreline. As Peter Dutton has explained, a “substantial majority” of the international community views the airspace above waters located within a coastal state’s EEZ as an international navigational commons, such that even military aircraft are generally free to operate without interference. By Dutton’s calculation, no more than sixteen states have adopted a contrary view—Bangladesh, Brazil, Burma, Cape Verde, China, Guyana, India, Kenya, Iran, Malaysia, the Maldives, Mauritius, North Korea, Pakistan, Portugal, and Uruguay. A number of other countries—including the United States—have established expansive ADIZs, but have also reportedly declined to enforce them in a way that interferes with the navigation of foreign military aircraft not bound for territorial airspace. In the 1980s, the United States even engaged in hostilities with Libya to push back against Libya’s attempts to impose a large ADIZ over the Mediterranean. China’s new ADIZ appears to be largely co-extensive with its EEZ. As a result, the legality of the ADIZ is tenuous insofar as the majority practice reflects customary international law, and insofar as China plans to use the ADIZ to assert regulatory powers that are more robust than the custom permits. Of course, uncertainties remain. It’s unclear, for example, whether China will in fact enforce the ADIZ in an aggressive manner. And it’s conceivable that China has achieved the status of a persistent objector so as to exempt itself from the customary rule. Yet in the past China has affirmed that “all countries enjoy the freedom of overflight in the exclusive economic waters of a nation,” and has routinely declined to protest American reconnaissance flights in the airspace over the Chinese EEZ. In comparison to that practice, the ADIZ looks like a shift in strategy and further evidence of a growing Chinese readiness to assert itself in the region.