Since 16 July 1945, when the first atomic bomb was detonated at the Trinity test site near Alamogordo, New Mexico, mankind has lived with nuclear weapons. Each year, the number of bombs has grown, until now there are some fifty thousand warheads in the world, possessing the explosive yield of roughly twenty billion tons of TNT, or one million six hundred thousand times the yield of the bomb that was dropped by the United States on the city of Hiroshima after the Trinity explosion. These bombs were built as ‘weapons’ for ‘war’, but their significance greatly transcends war and all its causes and outcomes. They grew out of history, yet they threaten to end history. They were made by men, yet they threaten to annihilate man. They are a pit into which the whole world can fall – a nemesis of all human intentions, actions, and hopes. Only life itself, which they threaten to swallow up, can give the measure of their significance. Yet in spite of the immeasurable importance of nuclear weapons, the world has declined, on the whole, to think about them very much. We have thus far failed to fashion, or to discover within ourselves, an emotional or intellectual or political response to them. This peculiar failure of response, in which hundreds of millions of people acknowledge the presence of an immediate, unremitting threat to their existence and to the existence of the world they live in but do nothing about it – a failure in which both self-interest and fellow-feeling seem to have died – has itself been such a striking phenomenon that it has to be regarded as an extremely important part of the nuclear predicament itself. It is only very recently in Europe and the United States that public opinion has been stirred, and that ordinary people may be beginning to ask themselves how they should respond to the nuclear peril.

In what follows, I shall offer some thoughts on the origins and the significance of this predicament, on why we have so long resisted attempts to think about it (we even call a nuclear holocaust ‘unthinkable’) or deal with it, and on the shape and magnitude of the choice that it forces upon us. But first I wish to describe the consequences for the world, insofar as these can be known, of a full-scale nuclear holocaust at the current level of global armament. We have lived in the shadow of nuclear arms for more than thirty-six years, so it does not seem too soon for us to familiarize ourselves with them – to acquaint ourselves with such matters as the ‘thermal pulse’, the ‘blast wave’, and the ‘three stages of radiation sickness’. A description of a full-scale holocaust seems to be made necessary by the simple but basic rule that in order to discuss something one should first know what it is. A considerable number of excellent studies concentrating on various aspects of the damage that can be done by nuclear arms do exist, many of them written only in the last few years. Drawing on them and other printed sources, and also on interviews that I conducted recently with a number of scientists, I have attempted to piece together an account of the principal consequences of a full-scale holocaust. Such an account, which in its nature must be both technical and gruesome, cannot be other than hateful to dwell on, but it may be only by now descending into this hell in imagination that we can hope to escape descending into it in reality at some later time.

Whereas most conventional bombs produce only one destructive effect – the shock wave – nuclear weapons produce many destructive effects. At the moment of the explosion, when the temperature of the weapon material, instantly gasified, is at the superstellar level, the pressure is millions of times the normal atmospheric pressure. Immediately, radiation, consisting mainly of gamma rays, which are a very high-energy form of electromagnetic radiation, begins to stream outward into the environment. This is called the ‘initial nuclear radiation’, and is the first of the destructive effects of a nuclear explosion. In an air burst of a one-megaton bomb – a bomb with the explosive yield of a million tons of TNT, which is a medium-sized weapon in present-day nuclear arsenals – the initial nuclear radiation can kill unprotected human beings in an area of some six square miles.