Our future life on Earth depends on the state of the ocean

When we observe the ocean we rarely peek beneath its surface. As Helen Czerski shows in her lively and engrossing account of the physics of ocean spaces, we would not see much anyway. Sounds travel well in water, and blue whales talk to one another across thousands of miles; but light soon disappears, apart from the glow emitted by luminous fish. Historians of the oceans (myself included) have looked at how, when and why people have crossed the surface of these spaces, uninhabitable except in the security of a boat or on islands, such as those in Polynesia with which Czerski begins her book. But we need to dive deeper.

Out in Hawaii, she points out, ‘the ocean is as much part of home as the land’, and it was only from space that we have been able to appreciate the vast extent of Earth’s blue oceanic covering – 70 per cent of the globe, with the Pacific encompassing almost an entire hemisphere. And although we divide the ocean into several different ones, it is ultimately (as the ancient Greeks insisted) one big connected Okeanos. For Czerski, getting to the moon was a lesser achievement than seeing the Earth from there, and that sight should make us think more deeply about our responsibilities towards the planet, which is likely to be humanity’s only home, even if bubbles of settlement are created on the moon or Mars.

The argument about human responsibility is an undercurrent running through Blue Machine, and it is handled very deftly. Unlike some recent literature on the oceans, such as Callum Roberts’s powerful Ocean of Life, Czerski’s account is not impregnated with constant alerts about the damage we are certainly doing to a vast space upon which we depend much more than we realise.