The Long Summer: how climate changed civilisation Brian Fagan Granta Books, 284pp, £20 ISBN 1862076448

When confronted with the perils of global warming, sceptical people tend to ask: "Hasn't the climate always changed?" History certainly appears to support this contention. In medieval times, grapes were grown in the north of Britain, and the Vikings settled in Greenland before they were driven out by a sudden shift towards colder conditions. Buried within Brian Fagan's fascinating new book, however, lies a conclusive answer to the sceptics.

The fate of human civilisations has always been inextricably bound up with climate. The early Mediterranean kingdoms were devastated by a 300-year drought that began in 2200BC, destroying the fearsome Akkadian empire, centred in modern-day Syria, and tearing apart the social order of Old Kingdom Egypt. Around 900AD, a series of crippling droughts caused the collapse of the great Mayan city states of Copan, Palenque and Tikal. The suffering must have been immense. Remains from a house midden at Tikal show signs of burning and chewing - which, Fagan points out, "could only have come from survival cannibalism, when desperate people had nothing to eat except one another".

Nor is it just ancient kingdoms that were affected. The "great rains" of 1315-21 caused a million and a half people across western Europe to die from hunger and famine-related epidemics. This miserable episode marked the beginning of the Little Ice Age, a six-century cold period that resulted in frost fairs on the Thames and Alpine villages being overwhelmed by glaciers, and also produced the Dickensian ideal of the white Christmas. By 1850, the world was warming up again, a change that coincided with the industrial revolution, which in little more than a century was to affect the planet's atmosphere in ways that had never been seen.

So, to answer the sceptics' question - yes, the climate has always changed naturally. The Little Ice Age, for example, came about as the result of small alterations in the amount of solar radiation received by the earth. The main ice ages were also largely sun-driven: orbital shifts called Milankovitch cycles altered the pattern of solar radiation in the northern hemisphere and allowed huge ice sheets to form in 100,000-year cycles.

But what is different about current global warming is that it has nothing to do with natural cycles or the sun. Greenhouse-gas concentrations in the atmosphere are now at their highest levels since 20 million years ago, well before the Ice Age cycles began, when the earth was a very different and much hotter place.

Rather than providing succour to fatalists, Fagan's study presents us with a clear warning. From the earliest hunter-gatherer tribes to the mightiest empires, human civilisation has been vulnerable to long-term changes in the weather. With six billion souls now depending on a complex globalised food web for sustenance, our continued existence is far more precarious than we imagine. Fagan shows that when civilisations collapse, it tends to happen very suddenly, and there is invariably appalling hardship and suffering. Armed with this knowledge, there is no reason why we should follow the Mayans and the Akkadians and descend into famine and war. But as yet, there is little sign that we are prepared to learn from their fate.

Mark Lynas is the author of High Tide: news from a warming world (Flamingo)

Post your comment

Please note: you will need to login or register before you can comment on the website