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In The Dance of Air and Sea: How oceans, weather and life link together, Arnold Taylor explores these complex but vital links

OCEAN currents move water about the Earth on a scale that defeats human imagination 鈥� who can picture a flow equivalent to 800 Amazons? 鈥� yet you can read their shifting paths in the life of a daisy growing by a road. It鈥檚 like astrology, only scientific.

The central puzzle of oceanographer Arnold Taylor鈥檚 book is how variation in the Gulf Stream, the current that flows from the Caribbean to north-west Europe, affects things living far from it. In particular, Taylor looks at microscopic crustaceans called copepods that live in the North Sea. In years when the current鈥檚 path shifts to the north, you get more copepods; when it moves south, fewer.

Solving this riddle involves getting to grips with three complex subjects: oceanography, meteorology and ecology. Taylor does an excellent job of preparing the ground while also leavening the mix with quirky facts, such as what global warming will do for kidney stones, potted biographies of key players, and tales of nautical derring-do. Once he has explained how each part works in isolation, he moves on to the even trickier subject of how they interact.

The dominant member of the trio seems to be the atmosphere. The Gulf Stream is often credited with north-west Europe鈥檚 balmy climate, relative to places on the same latitude in Canada. In fact, it has little to do with this: the Rockies, which divert winds south before they blow eastwards across the Atlantic, are much more important. In general, the air has more influence on the oceans than vice versa.

We still don鈥檛 know why the Gulf Stream and copepods vary together. Taylor doesn鈥檛 quite deliver on that 鈥淗ow鈥� in his subtitle, meaning that his book, like the science on which it is based, is a bridge with sturdy foundations but as yet no middle. But from what we do know, it seems that both are responding to the climate, in particular to the rocking of an 鈥渁tmospheric see-saw鈥� called the North Atlantic Oscillation, which, by steering both the Gulf Stream and Europe鈥檚 weather, decides whether it is a good year for copepods or not.

Copepod population biology is an esoteric topic. But how these animals track the weather is part of the much more worrying question of how climate change will affect the various species on which we depend. In some parts of the North Sea, the copepods stopped mirroring the Gulf Stream in the mid-1990s, one of many biological responses to warming already seen around the world. Some of these responses may hold portents for our future, but, unlike the link between the Gulf Stream and the plankton, these are runes we have yet to learn to read. Taylor鈥檚 book shows how difficult, and how important, it is to decode them.