Apprehensions about uncontrolled thermonuclear fusion arose early in the Manhattan Project: Could explosion of a hydrogen bomb trigger a global physical catastrophe in starting chain reactions that seize the light elements and thus wipe out all life on Earth? It was not without grave anxiety that Emil Konopinski, Cloyd Marvin, Jr., and Gregory Breit ruled out this possibility. Since the end of World War II, public knowledge about 'the unthinkable', the consequences of nuclear war, was largely shaped by the horrible direct health effects of the 1945 atomic bombing of Hiroshima and Nagasaki, by the devastations and disruptions of life and infrastructure due to heat, blast and electromagnetic waves, prompt ionizing radiation, and radioactive fallout.
Public awareness of worldwide fallout risks was triggered by the fatal outcome of the atmospheric test Bravo, the largest weapon exploded by the United States (Bikini atoll, 28 February 1954; 15 Mt TNT equivalent).
y We are mournful about the loss of our friend and colleague Yuri Mikhailovich Svirezhev who passed away during the time of working on this paper. We dedicate our own contribution to his memory. (GS & PC)
Temporary geophysical effects of atmospheric tests, such as planetary pressure waves, magnetic field distortions, or ionospheric disruptions causing blackout in radio communication, were frequently recorded. A signature in worldwide weather was not found, however. The largest weapon ever tested, the 'Tsar of Bombs', a more than 50 Mt 'clean' bomb (with a nonfissionable mantle), was exploded on 30 October 1961, above the northern Soviet test site at Novaja Zemlya. Its pressure wave circled the Earth several times. The most obvious long-term, large-scale direct geophysical effect of nuclear explosions appears to have been caused by the Starfish Prime test on 9 July 1962 - a 1.4 Mt detonation some 400 km above the Johnston Island area in the tropical central North Pacific. An artificial (mini-van Allen radiation) belt of charged particles was trapped by the Earth's magnetic field and traced for a couple of years. High-altitude nuclear explosions may 'blind' reconnaissance satellites, impair electronics over vast areas, and even inflict on a missile attack, by their electromagnetic pulse (EMP).
Radioactive tracers from the 539 atmospheric test explosions until 1980, with an aggregate yield of about 440 Mt, will remain identifiable worldwide for millennia. Hot spots at test sites and the unresolved issue of low-dose radiation effects notwithstanding, though, their health effects are far from endangering the species of man. In a nuclear war, the number of warheads and their total explosive yield might exceed these figures by an order of magnitude, and the period of 35 years would reduce to a couple of days, if not hours. Such a 10 -fold 'compaction' of interacting effects rules out extrapolation from the test series, as do consequences of a decisive distinction in targeting: The deadly logic of 'mutual assured destruction' (MAD) bears attacks on large population centers. Cities would also not escape 'countervalue' and 'counter-force' strikes against the economic and military potential, notably the command, control, communication, and intelligence (C I) structures. Not only does this turn 'warfare' into 'exchange', it also gives birth to a new quality of risks - the long-term, worldwide indirect aftereffects that add to and interfere with the disastrous direct effects of nuclear explosions.
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