Wrong choices and lethal lessons

The Vikings, who took ample stocks of myth with them on their travels, might have made a fine legend out of their own various fates. Their ships were like maritime seed-pods tossed by the gods on to this shore and that.

One handful of Norse seeds landed in Greenland, where their descendants lasted for several centuries. Another pitched up on Iceland, where the stock has survived by the skin of its teeth to the present day. Those blown as far as America lasted only a few years; nearer home, others found their way to France, becoming Normans and subsequently part of us.

Jared Diamond makes a parable, told in a scientific idiom, out of these mixed fortunes. His message is that a society's fate can rarely be ascribed to a single force, such as global warming, soil erosion, barbarians or stupidity. Environmental pressures are present in all his case studies, from the Arctic to the Pacific, but their effects vary according to the choices societies make.

He identifies five key factors: climate change, hostile neighbours, friendly trading partners, the damage people inf lict on their environments, and how they respond to their environmental problems. All can be seen at work in Viking history.

The Norsemen might have lasted longer in Greenland and America if their first impulse on seeing natives had not been to kill them, or if they had been prepared to admit that Inuit parkas would have suited them better than the latest fashions from medieval Europe.

But as Diamond's Icelandic friends told him, harsh surroundings foster a rigid mindset, for experience teaches that changes are likely to make things worse. And by the time experience has taught its lessons, the damage may be irreparable.

To the Vikings the Icelandic highlands looked like those of Scotland, so they stocked them with sheep as they had in Britain. Only when it was too late did they learn that Iceland's vegetation was no match for the livestock, and the soil, formed from volcanic ash, would blow away once exposed. The resulting landscape was latterly used to prepare astronauts for exploring the Moon.

Diamond notes with wry satisfaction that archaeologists push at open doors in Iceland, where it is taken for g ranted that studying medieval events might help in tackling modern problems.

The success of his book derives from his ability to make that case to a wider audience. He is singularly qualified: an expert on the birds of New Guinea, an ecologist, an environmental historian and a Californian professor resident in the smoggy sprawl of Los Angeles.

COLLAPSE combines a panoramic understanding of ecological and historical processes with a feeling for places and people that comes from a lifetime spent under different roofs and different skies. This wisdom gives it an air of serenity despite its turbulent and tragic stories.