‘For years we thought the oceans were so vast and the inhabitants so infinitely numerous that nothing we could do could have an effect upon them. But now we know that was wrong.’ Sir David Attenborough’s sentiments, expressed in the final episode of Blue Planet II, a 2017 BBC series watched by hundreds of millions worldwide, are shared by both Chris Armstrong and Charles Clover. They don’t mention it, but Blue Planet II raised to a new level global consciousness of the multi-fronted assault on the health and bounty of our oceans. As land-based assets are depleted, the scramble for oceanic resources accelerates. Existing regulatory arrangements, shaped by the UN Convention on the Law of the Sea, are ill-equipped to meet pressing challenges such as the survival of small island nations jeopardised by rising waters and the acute global crisis of marine biodiversity. We are at sea.

How we get out of this mess is Armstrong’s central concern in A Blue New Deal (a phrase coined in 2019 by David Helvarg, founder of the American campaign group Blue Frontier). A political theorist, Armstrong explains how the notion of an inexhaustible oceanic frontier is buttressed by the doctrine of freedom of the high seas (mare liberum): no person, company or country enjoys exclusive access to, let alone control or ownership of, the oceans and their resources. The more restrictive notion of closed sea (mare clausum) underpins a maritime state’s sovereign control of its territorial waters, as well as the exclusive economic zones (EEZs) that stretch two hundred nautical miles from its coast.

In place of the principles of mare liberum and mare clausum, Armstrong advocates that of res communis: collective governance of a decolonised ocean in the interests of all people and marine creatures. Within his ‘blue water thinking’ he sees a new ocean order as a ‘potential birthing