tons of nitric oxide is produced for
each megaton of nuclear explosive power.

What would be the effects of nitric oxides driven into the stratosphere
by an all-out nuclear war, involving the detonation of 10,000 megatons
of explosive force in the northern hemisphere? According to the recent
National Academy of Sciences study, the nitric oxide produced by the
weapons could reduce the ozone levels in the northern hemisphere by as
much as 30 to 70 percent.

To begin with, a depleted ozone layer would reflect back to the earth's
surface less heat than would normally be the case, thus causing a drop
in temperature--perhaps enough to produce serious effects on
agriculture. Other changes, such as increased amounts of dust or
different vegetation, might subsequently reverse this drop in
temperature--but on the other hand, it might increase it.

Probably more important, life on earth has largely evolved within the
protective ozone shield and is presently adapted rather precisely to
the amount of solar ultraviolet which does get through. To defend
themselves against this low level of ultraviolet, evolved external
shielding (feathers, fur, cuticular waxes on fruit), internal shielding
(melanin pigment in human skin, flavenoids in plant tissue), avoidance
strategies (plankton migration to greater depths in the daytime,
shade-seeking by desert iguanas) and, in almost all organisms but
placental mammals, elaborate mechanisms to repair photochemical damage.

It is possible, however, that a major increase in solar ultraviolet
might overwhelm the defenses of some and perhaps many terrestrial life
forms. Both direct and indirect damage would then occur among the
bacteria, insects, plants, and other links in the ecosystems on which
human well-being depends. This disruption, particularly if it occurred
in the aftermath of a major war involving many other dislocations,
could pose a serious additional threat to the recovery of postwar
society. The National Academy of Sciences report concludes that in 20
years the ecological systems would have essentially recovered from the
increase in ultraviolet radiation--though not necessarily from
radioactivity or other damage in areas close to the war zone. However,
a delayed effect of the increase in ultraviolet radiation would be an
estimated 3 to 30 percent increase in skin cancer for 40 years in the
Northern Hemisphere's mid-latitudes.

SOME CONCLUSIONS

We have considered the probl