"Yet the state of the high seas is deteriorating (see article). Arctic ice now melts away in summer. Dead zones are spreading. Two-thirds of the fish stocks in the high seas are over-exploited, even more than in the parts of the oceans under national control. And strange things are happening at a microbiological level. The oceans produce half the planet's supply of oxygen, mostly thanks to chlorophyll in aquatic algae. Concentrations of that chlorophyll are falling. That does not mean life will suffocate. But it could further damage the climate, since less oxygen means more carbon dioxide."
In 1968 an American ecologist, Garrett Hardin, published an article entitled "The Tragedy of the Commons". He argued that when a resource is held jointly, it is in individuals' self-interest to deplete it, so people will tend to undermine their collective long-term interest by over-exploiting rather than protecting that asset. Such a tragedy is now unfolding, causing serious damage to a resource that covers almost half the surface of the Earth.
The high seas—the bit of the oceans that lies beyond coastal states' 200-mile exclusive economic zones—are a commons. Fishing there is open to all. Countries have declared minerals on the seabed "the common heritage of mankind". The high seas are of great economic importance to everyone—fish is a more important source of protein than beef—and getting more so. The number of patents using DNA from sea-creatures is rocketing, and one study suggests that marine life is a hundred times more likely to contain material useful for anti-cancer drugs than is terrestrial life.