s
at distances of up to 600 miles from the burst point.

Yet another surprise was the discovery that electromagnetic pulses can
play havoc with electrical equipment itself, including some in command
systems that control the nuclear arms themselves.

Much of our knowledge was thus gained by chance--a fact which should
imbue us with humility as we contemplate the remaining uncertainties
(as well as the certainties) about nuclear warfare. What we have
learned enables us, nonetheless, to see more clearly. We know, for
instance, that some of the earlier speculations about the after-effects
of a global nuclear war were as far-fetched as they were
horrifying--such as the idea that the worldwide accumulation of
radioactive fallout would eliminate all life on the planet, or that it
might produce a train of monstrous genetic mutations in all living
things, making future life unrecognizable. And this accumulation of
knowledge which enables us to rule out the more fanciful possibilities
also allows us to reexamine, with some scientific rigor, other
phenomena which could seriously affect the global environment and the
populations of participant and nonparticipant countries alike.

This paper is an attempt to set in perspective some of the longer term
effects of nuclear war on the global environment, with emphasis on
areas and peoples distant from the actual targets of the weapons.

THE MECHANICS OF NUCLEAR EXPLOSIONS

In nuclear explosions, about 90 percent of the energy is released in
less than one millionth of a second. Most of this is in the form of
the heat and shock waves which produce the damage. It is this
immediate and direct explosive power which could devastate the urban
centers in a major nuclear war.

Compared with the immediate colossal destruction suffered in target
areas, the more subtle, longer term effects of the remaining 10 percent
of the energy released by nuclear weapons might seem a matter of
secondary concern. But the dimensions of the initial catastrophe
should not overshadow the after-effects of a nuclear war. They would
be global, affecting nations remote from the fighting for many years
after the holocaust, because of the way nuclear explosions behave in
the atmosphere and the radioactive products released by nuclear bursts.

When a weapon is detonated at the surface of the earth or at low
altitudes, the heat pulse vaporizes the bomb material, target, nearby
structures, and underlying so