continuously evolving.

Only recently, new light was shed on the subject in a study which the Arms
Control and Disarmament Agency had asked the National Academy of Sciences
to undertake. Previous studies had tended to focus very largely on
radioactive fallout from a nuclear war; an important aspect of this new
study was its inquiry into all possible consequences, including the effects
of large-scale nuclear detonations on the ozone layer which helps protect
life on earth from the sun's ultraviolet radiations. Assuming a total
detonation of 10,000 megatons--a large-scale but less than total nuclear
"exchange," as one would say in the dehumanizing jargon of the
strategists--it was concluded that as much as 30-70 percent of the ozone
might be eliminated from the northern hemisphere (where a nuclear war would
presumably take place) and as much as 20-40 percent from the southern
hemisphere. Recovery would probably take about 3-10 years, but the
Academy's study notes that long term global changes cannot be completely
ruled out.

The reduced ozone concentrations would have a number of consequences
outside the areas in which the detonations occurred. The Academy study
notes, for example, that the resultant increase in ultraviolet would cause
"prompt incapacitating cases of sunburn in the temperate zones and snow
blindness in northern countries . . "

Strange though it might seem, the increased ultraviolet radiation could
also be accompanied by a drop in the average temperature. The size of the
change is open to question, but the largest changes would probably occur at
the higher latitudes, where crop production and ecological balances are
sensitively dependent on the number of frost-free days and other factors
related to average temperature. The Academy's study concluded that ozone