"Ice, Mud and Blood" by Chris Turney

A chirpy, detailed book that delivers on past climate but not on present climate

Anyone new to the climate change debate is bound to wonder whether a 5-6 degree increase in temperatures is really all that bad - especially if the person is cold, English, and nostalgic for summer. A good reply to this wonderment is to say that the last time the globe was 5 or 6 degrees colder, there were glaciers in the South of England, and the melting ice caused Britain to split off from France.

Chris Turney, a geologist at the University of Exeter, knows as well as anyone that climates past have lessons for climates present. In Ice, Mud and Blood, Turney's humour and expertise make for a jaunty, fascinating account of how past climates worked and how scientists find out about them. But Turney spends little time linking past climate to present climate; so, as a contribution to the climate change debate, the book doesn't live up to its promise.

As Turney points out, it's a wonder that we know anything about past climate at all. Natural climate change occurs over vast periods, and events in the intervening millennia have played havoc with the evidence. Turney does a great job of showing how scientific detective work can, against the odds, give a clear and convincing picture of some key events in the last three-quarters of a billion years of earth weather.

To give one example: how could we possibly know that the tropics were covered in ice between 580 and 710 million years ago? As Turney explains, certain kinds of rocks tell us that glaciers once appeared in, among other places, Namibia; and the magnetism of the rocks assures us that those glaciers did indeed form at tropical latitudes. You might object - as some scientists did - that the earth had a bigger tilt back then, so that Namibia once swung around the freezing poles. A study of 'evaporites' - salt deposits from drying lakes that only occur in hot dry areas - puts paid to that objection, as do ocean deposits of iridium. As this example hints, paleo-climatologists can get technical at times. But their work is as impressive as cosmologists probing into deep space or particle physicists getting into the guts of an atom.

The instruments used to detect past climates have their own fascination. The ice cores of Greenland and Antarctica - pipes of ancient ice, kilometres in length, drawn from some of the world's most inhospitable climates - make for a good story, and Turney tells it well. Because these 'archives' of past climate are so hard to read, paleo-climatology is also tale of wrong turns, misinterpretations and dead-ends. Where there is just not enough data for scientists to draw solid conclusions - about the effect of climate change on cyclones in the Western Atlantic, for example - Turney is not afraid to say so. Where multiple sets of data converge on the same conclusion, he drives the point home.

Turney's chirpy prose is helped along by sketches of the charismatic pioneers and hard-bitten explorers in the science of weather. Extra spice comes from Turney's taste for history, love of hands-on research, and nose for a big idea. The big ideas include some intriguing conjectures about the interaction of climate and early humans. For example, Turney argues that the concentration of diabetes in Northern Europe could be explained as an evolutionary response to the Younger Dyas, a cold period in the North Atlantic that ended around 10,000 BC.

Turney is rock-solid on the science of past climates, but cracks start to appear when he draws conclusions about current climate change. The problem starts with the book's structure. It is arranged as a chronology of past climate, not as an argument for the state of current climate. Turney tries to link past to present in a final conclusion, where he asks 'What does this all mean for the future?' But it's all a bit vague and last-minute. He simply draws some general lessons from the preceding 192 pages of history: greenhouse gases can power massive changes in climate; feedback effects can amplify small changes; and human action can rearrange our land, sea and atmosphere on a large scale. Compared to the quantitative detail of the other chapters, this conclusion is just hand-waving.

There is no doubt that, in the past, human activity, high temperatures, and high levels of methane and carbon dioxide, all caused big - sometimes cataclysmic - changes to weather and geography. But is our current situation quantitatively similar to those past changes? Turney does not give a clear case. When he asks the numbers question, his answer is a short account of the famous 'hockey-stick' study, a comparison of temperature changes in the last century with those over the previous millennium. One wonders what happened to the previous seven chapters and the previous 700 million years they cover. Do the most recent climates give the best lessons, after all?

A determined reader might dig through the chapters to see if Turney makes the link between past climate to present climate on the run. Such a reader will find a number of hearty calls to action, but little hard-and-fast argument. For example, Turney emphasises the role of CO2 in the warming that occurred during the Eemian period around 120,000 years ago. But he also emphasises that increases in carbon dioxide lagged behind the warming. And the evidence he cites for CO2-driven warming considers just one ice core and takes up one paragraph. On some topics - such as the dynamics of melting ice - Turney makes a stronger case, but only with the help of models and evidence drawn from studies of present-day climate.

Ice, mud and Blood could have been more streamlined and persuasive. As a call to action on climate change, it is a missed opportunity. But as a story of scientific ingenuity and the wonders of nature, it takes every chance - and succeeds.