IT MATTERS THAT one should understand the provenance of this important and disturbing book. It is not another futurological diatribe saying that the end is nigh, but a lucid, calm, profoundly well-informed work by a distinguished scientist, whose humanity - evidenced by a serious ethical commitment and a quiet sense of humour - balances the dispassionate logic with which he surveys his subject: the multitude of threats facing humanity in the twenty-first century from error and terror in the nuclear, biological and environmental spheres.

While it contains no element of scaremongering, the conclusion Martin Rees reaches is a deeply disquieting one. To put a number on it, humankind has, in his considered view, only about a 50 per cent chance of surviving the century - at least without one or more major catastrophes that