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Nuclear Winter: A Status Report
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10238 |
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Section : |
MODERN THOUGHT
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| Issue
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8 / 1986 |
5,594 Words |
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Thomas P. Ackerman
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It is now about two and a half years since the issue of the climate consequences of nuclear war (sometimes called nuclear winter) was first brought to the attention of the American public. Since that time, a number of technical articles have been published on the subject, which examine various aspects of the original study in more detail or extend the calculations with more detailed computer models. Comprehensive scientific reviews of the problem have also been commissioned by the National Academy of Sciences, the Royal Society of Canada, and the International Council of Scientific Unions (ICSU). As a result of this intense scrutiny, a great deal has been learned about the possible climatic consequences of nuclear war, and, while many uncertainties remain to be resolved, there is a growing consensus among the scientific community that the problem is both real and urgent.
The basic steps in the casual chain connecting nuclear war and potential climatic catastrophe can be stated fairly simply. Nuclear bombs, particularly those detonated slightly above the surface of the earth, are remarkably efficient incendiary exchange between the superpowers, many fires would be ignited and burn out of control, injecting millions of tons of black smoke into the atmosphere, which would prevent the sunlight incident on the planet from reaching the ground. The ground and the atmosphere below the pall of smoke would consequently become so cold that frosts and freezing conditions might occur even in mild-summer. The smoke would eventually be dispersed around the globe by the atmosphere, bringing the cold and the dark to countries not directly involved in the nuclear holocaust.
In the discussion that follows, each of the steps in the chain will be briefly elaborated and an attempt made to assess the strengths and weaknesses of the assumptions involved. For more detailed treatment of the issues, the interested reader is referred to the recent report prepared for the Scientific Committee on Problems of the Environment (SCOPE) as requested by ICSU, which serves as the basic reference work for the material presented here.
Weapons Effects And Scenarios
Nuclear-weapon detonations are usually divided into surface bursts and airbursts. The former would be used against such hardened military targets as missile silos and command bunkers. They typically loft large amounts of dust into the atmosphere through a variety of physical mechanisms that include (1) vaporizing the soil by the high temperature and pressure of the explosion followed by condensation in the atmosphere (2) blowoff of soil as a result of steam formation in the soil by the intense thermal radiation, and (3) suction of dust and debris by the ascending fireball. Surface bursts result further in high levels of prompt radioactive fallout. Airbursts would be used against soft military targets such as air fields and submarine-port facilities and against such industrial targets as factories for building missiles or airplanes. They typically produce less dust and local fallout, but are far more effective at igniting fires.
When a nuclear weapon is detonated, the released energy forms a giant fireball that is roughly the temperature of the sun. The tremendous heat radiated by the fireball can spontaneously ignite combustible materials such as wood or plastics much as sunlight focused through a lens ignites paper or wood. Typical airbursts can cause ignition at distances as great as
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