Chilly tale of ale fad

Almost legendary, but still amazing, is the story of the Viking adventurers sailing westwards a thousand years ago and discovering all kinds of islands, Iceland, Greenland and finally, half a millennium before Columbus, North America, or Wineland, as Leif Erikson called it. Viking settlements flourished for centuries and transatlantic trade was common until the sea links were interrupted by a southerly moving edge of pack ice. The American villages were cut off, the settlements in Greenland declined and eventually even the population of Iceland shrank to such a degree that the government in Copenhagen discussed evacuation.

The Norse expansion is nowadays correlated with favourable climatic conditions, the medieval warm period, which allowed viticulture in England and Norway. The California-based archaeologist Brian Fagan, author of a pioneering study on climatic history, portrays the period in poetic language: "Summer after summer passed by with long dreamy days, golden sunlight, and bountiful harvests." This medieval dreamtime, however, was ruined by an unexpected long-term climatic deterioration, which has been labelled only recently as the little ice age, a global cooling less dramatic than the "great" ice ages, but strong enough to influence the course of history. It began in the 14th century and disappeared by the early 19th century. Well-known but hitherto unlinked historical phenomena, such as the collapse of the deserted villages in northern Europe, the rise of beer consumption and the advent of the bubonic plague, are being reinterpreted and subsumed under the auspices of a new historical agency: climatic change.

Until recently, the climate of historical times, in contrast to past geological periods, has been perceived as stable and reliable. Only since the 1960s have new scientific methods left no doubt as to continuous and more recent changes. Ice-core and sedimentation analyses have been performed worldwide, and their results have been convincingly synchronised with more traditional methods of climate assessment: tree-ring analysis, or the analysis of written sources. The reconstructed data about conditions of agriculture, price movements and demography are fitting together surprisingly well.

Fagan tries to summarise these recent developments in research for a wider audience. The British reader will be pleased by the nostalgia of an author who starts with impressions from his holidays in northern England and focuses his examples on the British Isles, with occasional references to other parts of the world. This deliberate parochialism contrasts sharply with the necessity to include accounts of far-off events. The English food riots of 1816 were supposedly triggered by the eruption of Mount Tambora in Indonesia, whose dust clouds - still to be found in glaciers and sediments between Alaska and New Zealand - are thought to have caused a noticeable drop in global temperature in 1816, the so-called "year without a summer". The tremendous rainfalls caused crop failures, price rises, malnutrition, epi-demic diseases and sharp rises in mortality, crime and suicide. Here was a global catastrophe before globalisation, with plenty of local consequences: a poverty crisis in Switzerland, a typhus epidemic in Glasgow, emigration from Yorkshire, a new constitution in Bavaria, canal building in New York and an outbreak of bubonic plague in India.

But it is one thing to suggest a link between particular climatic and human events, quite another to prove it. Fagan is too generous in suggesting causal relationships, for example his claim that the building of cathedrals was "an enduring legacy of the medieval warm period" or that modern welfare policies should be considered to be a result of the Tambora eruption. His central theme, "how climate made history", is never seriously discussed. Instead, he summarises discussions about possible reasons for climatic change, toying with such concepts as the El Ni$o effect, the North Atlantic oscillation, the greenhouse mechanism, ozone depletion and solar radiation.

This is regrettable. The little ice age is a good subject through which to gain insights into the impact of climatic change on human societies. The early modern period is the first to offer not only material remains but abundant written evidence: chronicles, diaries, correspondences and expert opinions. Climatic deterioration undoubtedly produced direct and obvious reactions, for example in changing patterns of nutrition and the abandonment of settlements. But there is also an element of contingency, since complex societies or civilisations are culturally determined to a considerable degree. Without scrutinising religious or theological issues, and in Europe particularly the idea of sin, it will be impossible to understand the changing attitudes towards sexuality, and therefore towards marriage patterns, fashion and social behaviour. Social conflicts and conflict management, rebellions, diplomacy and warfare depend at least in part on cultural patterns. They are, however, potentially fuelled by climatic influences. Medievalists must explore the interdependence of climatic deterioration and the crises of the later middle ages; early modernists the coincidence of cooling and Calvinism. The French wars of religion and large-scale witchcraft persecutions coincided with some of the worst years of the little ice age, when rivers and lakes were frozen all over Europe, and Brueghel invented the winter landscape as a new genre of painting.

Synchronicity and causation, however, are two different things and future discussions about the impact of the little ice age will probably be more demanding. We shall need densely argued pieces, taking into consideration the complexity of late medieval societies, in Europe and elsewhere, since climatic shifts were a worldwide experience. European historians will need to review the debates of the discipline in the light of new evidence: the transition from feudalism to capitalism for instance, or the "general crisis of the 17th century". The formation of nation states in western Europe, the agrarian revolution, the scientific revolution and the industrial revolution have to be reconsidered. Fagan's book is stimulating, an appetiser that hopefully does not spoil the main course.

Wolfgang Behringer is professor of history, University of York.