arge-scale injection of
dust into the stratosphere would reduce sunlight intensities and
temperatures at the surface, while increasing the absorption of heat in
the upper atmosphere.

The resultant minor changes in temperature and sunlight could affect
crop production. However, no catastrophic worldwide changes have
resulted from volcanic explosions, so it is doubtful that the gross
injection of particulates into the stratosphere by a 10,000-megaton
conflict would, by itself, lead to major global climate changes.

B. Ozone

More worrisome is the possible effect of nuclear explosions on ozone in
the stratosphere. Not until the 20th century was the unique and
paradoxical role of ozone fully recognized. On the other hand, in
concentrations greater than I part per million in the air we breathe,
ozone is toxic; one major American city, Los Angeles, has established a
procedure for ozone alerts and warnings. On the other hand, ozone is a
critically important feature of the stratosphere from the standpoint of
maintaining life on the earth.

The reason is that while oxygen and nitrogen in the upper reaches of
the atmosphere can block out solar ultraviolet photons with wavelengths
shorter than 2,420 angstroms (A), ozone is the only effective shield in
the atmosphere against solar ultraviolet radiation between 2,500 and
3,000 A in wavelength. (See note 5.) Although ozone is extremely
efficient at filtering out solar ultraviolet in 2,500-3,000 A region of
the spectrum, some does get through at the higher end of the spectrum.
Ultraviolet rays in the range of 2,800 to 3,200 A which cause sunburn,
prematurely age human skin and produce skin cancers. As early as 1840,
arctic snow blindness was attributed to solar ultraviolet; and we have
since found that intense ultraviolet radiation can inhibit
photosynthesis in plants, stunt plant growth, damage bacteria, fungi,
higher plants, insects and annuals, and produce genetic alterations.

Despite the important role ozone plays in assuring a liveable
environment at the earth's surface, the total quantity of ozone in the
atmosphere is quite small, only about 3 parts per million.
Furthermore, ozone is not a durable or static constituent of the
atmosphere. It is constantly created, destroyed, and recreated by
natural processes, so that the amount of ozone present at any given
time is a function of the equilibrium reached between the creative and
destructive chemical reactions and