Nuclear Winter

SCOPE, the non-governsental scientific group which reports to the UN through the International Council of Scientific Unions, has for the pa& 15 months been assembling a detailed report on the possibility of nuclear winter as a consequence of a major nuclear war. Recent workshops have brought together a number of experts from temperate and tropical regions with agriculturalists, preparatory to publication of a final two-volume report by October, 1985, by Wiley (U.K.). Professor Tom Hutchinson of the U. of Toronto,organized a temperate system workshop March 20-23 at the University.

There now seams to be general agreement that a nuclear winter is likely to follow a major nuclear war and that its onset would occur within days of detonations. Assuming a northern war, winter would spread rapidly through the northern hemisphere followed by major climatic shifts in tropical regions as smoke and dust intruded into their stratospheres and upper tropospheres. Temperatures would fall below zero even in summer for weeks or months. Below-normal temperatures of up to 5°C could persist for several years.

While the climatic data seem robust, predictions for changes in precipitation are only that it may be reduced by 25-100%, depending upon local conditions.

Biologists and ecologists focused upon effects on the dominant vegetation in various ecosystem.. If temperatures fell below freezing in the tropics for more than a few days forests would die, as would the animals in them. In temperate ecosystems, prospects for survival would be much better. The tundra was believed able to recover even from a nuclear winter starting in the summer. Grasslands, deciduous forests and deserts were considered much more vulnerable. For recovery, much would depend upon banks of viable soil-stored seed which can often survive and germinate after long periods. In the first year of a nuclear winter almost no crops could ripen, so food production for survivors would be close to zero. Even temperature drops of 3-5% from present levels would be sufficient to eliminate almost all wheat, corn and soybean harvests.

The nuclear winter studies for SCOPE are comprehensive and global. While many uncertainties and details are missing, what is known presents a grim picture of conditions over the world following a nuclear war. The problems of radioactive fallout and dust have not been considered here.

– Tom Hutchinson