Multiple upper-atmosphere nuclear bursts might be scheduled for a ballistic missile defense (BMD) system's 'terminal phase defense' under the threat of a 'decapitation' strike. This would endanger the Earth's 'ozone screen' in generating high amounts of nitrogen oxides (NO*). Rising fireballs of tropospheric bursts would have the same effect. The biologically active part of the solar ultraviolet radiation (UV-B), which causes structural change in amino acids and is normally absorbed by stratospheric ozone molecules, would then reach the surface. According to the US National Academy of Sciences (NAS; 1975), a 10 000Mt exchange could cause a hemispheric ozone loss by 30-70% that would extend globally, with potentially grave impacts on terrestrial and aquatic ecosystems, and recovery over years. The amount of stratospheric dust, injected by megaton-yield near-surface explosions, may resemble the aerosol load due to the Krakatau eruption in 1883. NAS thus took a surface cooling of only a few tenths of a degree centigrade for plausible, but expressed another concern: ''It is not known whether climatic variables have stable equilibrium values and a tendency to relax after an impulse disturbance such as that generated by a nuclear exchange.'' This led the authors to conclude that irreversible climatic shifts cannot be ruled out.
Criticism by the Federation of American Scientists (FAS) for too 'optimistic' NAS conclusions about potential impacts on remote, noncombatant countries became justified 7 years later. Invited to contribute on ozone impacts to a first international, comprehensive nuclear war risk study commissioned by the Royal Swedish Academy of Sciences and first published in its environmental journal AMBIO (1982), Paul Crutzen and John Birks were surprised to find unknown, severe effects due to the smoke from 'postnuclear' fires. A key mechanism like this was missing since the early speculations on changes of weather and climate due to nuclear war.
To grip consequences of the changing military policy away from 'assured destruction', the US Office of Technology Assessment (OTA; 1979) had just analyzed a range of scenarios in an influential war risk study, from attacks on cities and oil refineries to one-sided counter-force and countervalue strikes. High-altitude bursts were mentioned as critical but not addressed, though doubts were cast on massive stratospheric ozone depletion. The chemical system was better known then, and high-yield weapons had given way to missiles with multiple warheads of lower yield each. Focusing on direct effects of nuclear attacks, civil defense, economic breakdown, recovery and societal impacts, OTA suggests that extreme uncertainties, and certainty about disastrous 'minimum' consequences, both ''play a role in the deterrent effect of nuclear weapons''.
Other than OTA, the AMBIO study used a global reference exchange that comprises ground and tropo-spheric bursts with a total yield of about 5750 Mt. Crutzen and Birks confirmed both the NAS estimates of ozone depletion and the OTA doubts, that is, their advanced ozone model did not qualitatively alter the results, but the evolving strategic arsenals apparently did. In addition, they identified large-scale forest fires and intense urban and industrial conflagrations as sources of a long-lasting photochemical smog over large areas of the Northern Hemisphere. The sunlight needed for its formation, however, could be blocked by high amounts of smoke, notably when oil and gas fields or refineries were targeted. Smoke absorbs the short-wave solar flux and heats up, but interferes much less with the outgoing long-wave thermal radiation. The surface cools therefore, which would also suppress convection and reduce precipitation. Cold and darkness after a nuclear war would be severe for terrestrial ecosystems, but especially grave for oceanic food chains given the quick consumption of phytoplankton at the very base of the trophic web.
The anticipated climatic disruption triggered inquiry by Richard Turco, Owen Toon, Thomas Ackerman, James Pollack, and Carl Sagan (TTAPS), who were able to marshal the data for urban mass fires and fire storms not available in time to Crutzen and Birks, and to quantify the effect they coined 'nuclear winter' for a broad range of scenarios (100 Mt 'countercity', 5000 Mt 'baseline', 10 000Mt full-scale exchange, for example): a massive thermal inversion of the planetary atmosphere and its climatic consequences. A line of research which turned out to be essential addresses mass extinctions in Earth history, including hypotheses of extraterrestrial impacts and those that blame geological periods of enhanced volcanism or worldwide forest fires, maybe even all in combination. An authoritative circle of biologists and ecologists, led by a group including Paul Ehrlich, John Harte, Mark Harwell, Peter Raven, and George Woodwell, concluded that the extinction of man after a large nuclear war could no longer be ruled out. A public conference ''The World after Nuclear War'' (Washington, 31 October-1 November 1983) attracted unprecedented attention by communicating these findings, by the participation of scientists of both superpowers, and by a technique used on this occasion: a satellite TV bridge (Moscow-Washington) between both academies of sciences. Two research groups from either side of the globe exchanged their first 'nuclear winter' results, based on global climate models, via this public 'Moscow link:' Vladimir Aleksandrov and Georgiy Stenchikov, and Curt Covey, Steven Schneider and Starley Thompson.
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Disasters: Why No ones Really 100 Safe. This is common knowledgethat disaster is everywhere. Its in the streets, its inside your campuses, and it can even be found inside your home. The question is not whether we are safe because no one is really THAT secure anymore but whether we can do something to lessen the odds of ever becoming a victim.