nuclear winter scenarios

nuclear winter scenarios In 1983 the journal Science published a paper (known from the initials of its authors surnames as TTAPS) which suggested that a nuclear war could lead to a widespread cooling of the climate because the amount of radiation penetrating to the Earth's surface would be reduced as a result of smoke and dust (generated by fires) blanketing the atmosphere. Darkness could result over large areas with land temperatures being reduced to between −15 and −25 °C, which would have catastrophic biological consequences. In what is called the ‘baseline scenario’ of a nuclear war (10 000 explosions with a total yield of 5000 megatons) it is supposed that 1000 million tons of dust would be created, 80 per cent of which would find its way into the stratosphere. The atmosphere would be loaded with vastly more fine dust than even the largest volcanic eruptions in historical time have produced, and the dust clouds could therefore be expected to last longer and have a more protracted and drastic effect on the climate.

Some scientists believe that large horizontal and vertical temperature gradients caused by absorption of sunlight in smoke and dust clouds might induce strong monsoonal-type circulations leading to heavy snowfalls in some continental areas. Other authorities suggest that owing to reduced heating over the continental land masses in the northern hemisphere, the monsoon rains would be greatly reduced. It has also been suggested that a consequence of the extensive freeze would be the generation of large quantities of water vapour which would condense and fall as heavy rain. This would tend to wash out the suspended soot and dust from the atmosphere. Wash-out was not allowed for in the TTAPS model. The ozone layer might be damaged by the release of nitrogen oxides from nuclear explosions.

The original predictions came from a simple computer model and, as more realistic three-dimensional models were run, the more apocalyptic claims fell away. While the climate models that have been developed assume that nuclear explosions would result in a uniform smoke distribution covering much of the northern hemisphere, critics have pointed out that patchiness in the smoke cover could be very important. It was suggested by the late 1980s that if a war happened in July (the worst month) temperatures would fall by only a few degrees for up to a month instead of months of freezing darkness.

‘Nuclear winter’ is a hypothesis, and the detailed reasoning behind it is still under discussion. While the magnitude of the effects is not agreed, it can be argued that the policy implications that have resulted from the wide dissemination of such ideas might have helped to deter the initiation of a nuclear strike. Nuclear winter makes the climate consequences of a nuclear first strike unacceptable, even if there are doubts as to whether the effect would not be as severe as was originally suggested.

Allen Perry

Bibliography

TTAPS (1983) Nuclear winter: global consequences of multiple nuclear explosions. Science, 222, 1283–92.
Harwell, M. A. (1984) Nuclear winter. Springer-Verlag, New York.