Produced by Gregory Walker









For an HTML version of this document and additional public domain
documents on nuclear history, visit Trinity Atomic Web Site:
http://www.envirolink.org/issues/nuketesting/





WORLDWIDE EFFECTS OF NUCLEAR WAR - - - SOME PERSPECTIVES

U.S. Arms Control and Disarmament Agency, 1975.



CONTENTS


  Foreword
  Introduction
  The Mechanics of Nuclear Explosions
  Radioactive Fallout
    A. Local Fallout
    B. Worldwide Effects of Fallout
  Alterations of the Global Environment
    A. High Altitude Dust
    B. Ozone
  Some Conclusions

  Note 1: Nuclear Weapons Yield
  Note 2: Nuclear Weapons Design
  Note 3: Radioactivity
  Note 4: Nuclear Half-Life
  Note 5: Oxygen, Ozone and Ultraviolet Radiation



FOREWORD

Much research has been devoted to the effects of nuclear weapons.  But
studies have been concerned for the most part with those immediate
consequences which would be suffered by a country that was the direct
target of nuclear attack.  Relatively few studies have examined the
worldwide, long term effects.

Realistic and responsible arms control policy calls for our knowing
more about these wider effects and for making this knowledge available
to the public.  To learn more about them, the Arms Control and
Disarmament Agency (ACDA) has initiated a number of projects, including
a National Academy of Sciences study, requested in April 1974.  The
Academy's study, Long-Term Worldwide Effects of Multiple Nuclear
Weapons Detonations, a highly technical document of more than 200
pages, is now available.  The present brief publication seeks to
include its essential findings, along with the results of related
studies of this Agency, and to provide as well the basic background
facts necessary for informed perspectives on the issue.

New discoveries have been made, yet much uncertainty inevitably
persists. Our knowledge of nuclear warfare rests largely on theory and
hypothesis, fortunately untested by the usual processes of trial and
error; the paramount goal of statesmanship is that we should never
learn from the experience of nuclear war.

The uncertainties that remain are of such magnitude that of themselves
they must serve as a further deterrent to the use of nuclear weapons.
At the same time, knowledge, even fragmentary knowledge, of the broader
effects of nuclear weapons underlines the extreme difficulty that
strategic planners of any nation would face in attempting to predict
the results of a nuclear war.  Uncertainty is one of the major
conclusions in our studies, as the haphazard and unpredicted derivation
of many of our discoveries emphasizes. Moreover, it now appears that a
massive attack with many large-scale nuclear detonations could cause
such widespread and long-lasting environmental damage that the
aggressor country might suffer serious physiological, economic, and
environmental effects even without a nuclear response by the country
attacked.

An effort has been made to present this paper in language that does not
require a scientific background on the part of the reader.
Nevertheless it must deal in schematized processes, abstractions, and
statistical generalizations.  Hence one supremely important perspective
must be largely supplied by the reader: the human perspective--the
meaning of these physical effects for individual human beings and for
the fabric of civilized life.

 Fred C. Ikle
 Director
 U.S. Arms Control and Disarmament Agency



INTRODUCTION

It has now been two decades since the introduction of thermonuclear
fusion weapons into the military inventories of the great powers, and
more than a decade since the United States, Great Britain, and the
Soviet Union ceased to test nuclear weapons in the atmosphere.  Today
our understanding of the technology of thermonuclear weapons seems
highly advanced, but our knowledge of the physical and biological
consequences of nuclear war is 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 changes due to nuclear war might decrease global
surface temperatures by only negligible amounts or by as much as a few
degrees.  To calibrate the significance of this, the study mentioned
that a cooling of even 1 degree centigrade would eliminate commercial
wheat growing in Canada.

Thus, the possibility of a serious increase in ultraviolet radiation
has been added to widespread radioactive fallout as a fearsome
consequence of the large-scale use of nuclear weapons.  And it is
likely that we must reckon with still other complex and subtle
processes, global in scope, which could seriously threaten the health
of distant populations in the event of an all-out nuclear war.

Up to now, many of the important discoveries about nuclear weapon
effects have been made not through deliberate scientific inquiry but by
accident. And as the following historical examples show, there has been
a series of surprises.

"Castle/Bravo" was the largest nuclear weapon ever detonated by the
United States.  Before it was set off at Bikini on February 28, 1954,
it was expected to explode with an energy equivalent of about 8 million
tons of TNT.  Actually, it produced almost twice that explosive
power--equivalent to 15 million tons of TNT.

If the power of the bomb was unexpected, so were the after-effects.
About 6 hours after the explosion, a fine, sandy ash began to sprinkle
the Japanese fishing vessel Lucky Dragon, some 90 miles downwind of the
burst point, and Rongelap Atoll, 100 miles downwind.  Though 40 to 50
miles away from the proscribed test area, the vessel's crew and the
islanders received heavy doses of radiation from the weapon's
"fallout"--the coral rock, soil, and other debris sucked up in the
fireball and made intensively radioactive by the nuclear reaction.  One
radioactive isotope in the fallout, iodine-131, rapidly built up to
serious concentration in the thyroid glands of the victims,
particularly young Rongelapese children.

More than any other event in the decade of testing large nuclear
weapons in the atmosphere, Castle/Bravo's unexpected contamination of
7,000 square miles of the Pacific Ocean dramatically illustrated how
large-scale nuclear war could produce casualties on a colossal scale,
far beyond the local effects of blast and fire alone.

A number of other surprises were encountered during 30 years of nuclear
weapons development.  For example, what was probably man's most
extensive modification of the global environment to date occurred in
September 1962, when a nuclear device was detonated 250 miles above
Johnson Island.  The 1.4-megaton burst produced an artificial belt of
charged particles trapped in the earth's magnetic field.  Though 98
percent of these particles were removed by natural processes after the
first year, traces could be detected 6 or 7 years later.  A number of
satellites in low earth orbit at the time of the burst suffered severe
electronic damage resulting in malfunctions and early failure.  It
became obvious that man now had the power to make long term changes in
his near-space environment.

Another unexpected effect of high-altitude bursts was the blackout of
high-frequency radio communications.  Disruption of the ionosphere
(which reflects radio signals back to the earth) by nuclear bursts over
the Pacific has wiped out long-distance radio communications for hours
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 soil and rock, all of which become entrained
in an expanding, fast-rising fireball.  As the fireball rises, it
expands and cools, producing the distinctive mushroom cloud, signature
of nuclear explosions.

The altitude reached by the cloud depends on the force of the
explosion. When yields are in the low-kiloton range, the cloud will
remain in the lower atmosphere and its effects will be entirely local.
But as yields exceed 30 kilotons, part of the cloud will punch into the
stratosphere, which begins about 7 miles up.  With yields of 2-5
megatons or more, virtually all of the cloud of radioactive debris and
fine dust will climb into the stratosphere.  The heavier materials
reaching the lower edge of the stratosphere will soon settle out, as
did the Castle/Bravo fallout at Rongelap.  But the lighter particles
will penetrate high into the stratosphere, to altitudes of 12 miles and
more, and remain there for months and even years.  Stratospheric
circulation and diffusion will spread this material around the world.



RADIOACTIVE FALLOUT

Both the local and worldwide fallout hazards of nuclear explosions
depend on a variety of interacting factors: weapon design, explosive
force, altitude and latitude of detonation, time of year, and local
weather conditions.

All present nuclear weapon designs require the splitting of heavy
elements like uranium and plutonium.  The energy released in this
fission process is many millions of times greater, pound for pound,
than the most energetic chemical reactions.  The smaller nuclear
weapon, in the low-kiloton range, may rely solely on the energy
released by the fission process, as did the first bombs which
devastated Hiroshima and Nagasaki in 1945.  The larger yield nuclear
weapons derive a substantial part of their explosive force from the
fusion of heavy forms of hydrogen--deuterium and tritium.  Since there
is virtually no limitation on the volume of fusion materials in a
weapon, and the materials are less costly than fissionable materials,
the fusion, "thermonuclear," or "hydrogen" bomb brought a radical
increase in the explosive power of weapons.  However, the fission
process is still necessary to achieve the high temperatures and
pressures needed to trigger the hydrogen fusion reactions.  Thus, all
nuclear detonations produce radioactive fragments of heavy elements
fission, with the larger bursts producing an additional radiation
component from the fusion process.

The nuclear fragments of heavy-element fission which are of greatest
concern are those radioactive atoms (also called radionuclides) which
decay by emitting energetic electrons or gamma particles.  (See
"Radioactivity" note.) An important characteristic here is the rate of
decay.  This is measured in terms of "half-life"--the time required for
one-half of the original substance to decay--which ranges from days to
thousands of years for the bomb-produced radionuclides of principal
interest.  (See "Nuclear Half-Life" note.) Another factor which is
critical in determining the hazard of radionuclides is the chemistry of
the atoms.  This determines whether they will be taken up by the body
through respiration or the food cycle and incorporated into tissue.  If
this occurs, the risk of biological damage from the destructive
ionizing radiation (see "Radioactivity" note) is multiplied.

Probably the most serious threat is cesium-137, a gamma emitter with a
half-life of 30 years.  It is a major source of radiation in nuclear
fallout, and since it parallels potassium chemistry, it is readily
taken into the blood of animals and men and may be incorporated into
tissue.

Other hazards are strontium-90, an electron emitter with a half-life of
28 years, and iodine-131 with a half-life of only 8 days.  Strontium-90
follows calcium chemistry, so that it is readily incorporated into the
bones and teeth, particularly of young children who have received milk
from cows consuming contaminated forage.  Iodine-131 is a similar
threat to infants and children because of its concentration in the
thyroid gland. In addition, there is plutonium-239, frequently used in
nuclear explosives. A bone-seeker like strontium-90, it may also become
lodged in the lungs, where its intense local radiation can cause cancer
or other damage. Plutonium-239 decays through emission of an alpha
particle (helium nucleus) and has a half-life of 24,000 years.

To the extent that hydrogen fusion contributes to the explosive force
of a weapon, two other radionuclides will be released: tritium
(hydrogen-3), an electron emitter with a half-life of 12 years, and
carbon-14, an electron emitter with a half-life of 5,730 years.  Both
are taken up through the food cycle and readily incorporated in organic
matter.

Three types of radiation damage may occur: bodily damage (mainly
leukemia and cancers of the thyroid, lung, breast, bone, and
gastrointestinal tract); genetic damage (birth defects and
constitutional and degenerative diseases due to gonodal damage suffered
by parents); and development and growth damage (primarily growth and
mental retardation of unborn infants and young children).  Since heavy
radiation doses of about 20 roentgen or more (see "Radioactivity" note)
are necessary to produce developmental defects, these effects would
probably be confined to areas of heavy local fallout in the nuclear
combatant nations and would not become a global problem.


A. Local Fallout

Most of the radiation hazard from nuclear bursts comes from short-lived
radionuclides external to the body; these are generally confined to the
locality downwind of the weapon burst point.  This radiation hazard
comes from radioactive fission fragments with half-lives of seconds to
a few months, and from soil and other materials in the vicinity of the
burst made radioactive by the intense neutron flux of the fission and
fusion reactions.

It has been estimated that a weapon with a fission yield of 1 million
tons TNT equivalent power (1 megaton) exploded at ground level in a 15
miles-per-hour wind would produce fallout in an ellipse extending
hundreds of miles downwind from the burst point.  At a distance of
20-25 miles downwind, a lethal radiation dose (600 rads) would be
accumulated by a person who did not find shelter within 25 minutes
after the time the fallout began.  At a distance of 40-45 miles, a
person would have at most 3 hours after the fallout began to find
shelter.  Considerably smaller radiation doses will make people
seriously ill.  Thus, the survival prospects of persons immediately
downwind of the burst point would be slim unless they could be
sheltered or evacuated.

It has been estimated that an attack on U.S. population centers by 100
weapons of one-megaton fission yield would kill up to 20 percent of the
population immediately through blast, heat, ground shock and instant
radiation effects (neutrons and gamma rays); an attack with 1,000 such
weapons would destroy immediately almost half the U.S. population.
These figures do not include additional deaths from fires, lack of
medical attention, starvation, or the lethal fallout showering to the
ground downwind of the burst points of the weapons.

Most of the bomb-produced radionuclides decay rapidly.  Even so, beyond
the blast radius of the exploding weapons there would be areas ("hot
spots") the survivors could not enter because of radioactive
contamination from long-lived radioactive isotopes like strontium-90 or
cesium-137, which can be concentrated through the food chain and
incorporated into the body.  The damage caused would be internal, with
the injurious effects appearing over many years.  For the survivors of
a nuclear war, this lingering radiation hazard could represent a grave
threat for as long as 1 to 5 years after the attack.


B. Worldwide Effects of Fallout

Much of our knowledge of the production and distribution of
radionuclides has been derived from the period of intensive nuclear
testing in the atmosphere during the 1950's and early 1960's.  It is
estimated that more than 500 megatons of nuclear yield were detonated
in the atmosphere between 1945 and 1971, about half of this yield being
produced by a fission reaction.  The peak occurred in 1961-62, when a
total of 340 megatons were detonated in the atmosphere by the United
States and Soviet Union.  The limited nuclear test ban treaty of 1963
ended atmospheric testing for the United States, Britain, and the
Soviet Union, but two major non-signatories, France and China,
continued nuclear testing at the rate of about 5 megatons annually.
(France now conducts its nuclear tests underground.)

A U.N. scientific committee has estimated that the cumulative per
capita dose to the world's population up to the year 2000 as a result
of atmospheric testing through 1970 (cutoff date of the study) will be
the equivalent of 2 years' exposure to natural background radiation on
the earth's surface.  For the bulk of the world's population, internal
and external radiation doses of natural origin amount to less than
one-tenth rad annually.  Thus nuclear testing to date does not appear
to pose a severe radiation threat in global terms.  But a nuclear war
releasing 10 or 100 times the total yield of all previous weapons tests
could pose a far greater worldwide threat.

The biological effects of all forms of ionizing radiation have been
calculated within broad ranges by the National Academy of Sciences.
Based on these calculations, fallout from the 500-plus megatons of
nuclear testing through 1970 will produce between 2 and 25 cases of
genetic disease per million live births in the next generation.  This
means that between 3 and 50 persons per billion births in the
post-testing generation will have genetic damage for each megaton of
nuclear yield exploded.  With similar uncertainty, it is possible to
estimate that the induction of cancers would range from 75 to 300 cases
per megaton for each billion people in the post-test generation.

If we apply these very rough yardsticks to a large-scale nuclear war in
which 10,000 megatons of nuclear force are detonated, the effects on a
world population of 5 billion appear enormous.  Allowing for
uncertainties about the dynamics of a possible nuclear war,
radiation-induced cancers and genetic damage together over 30 years are
estimated to range from 1.5 to 30 million for the world population as a
whole.  This would mean one additional case for every 100 to 3,000
people or about 1/2 percent to 15 percent of the estimated peacetime
cancer death rate in developed countries.  As will be seen, moreover,
there could be other, less well understood effects which would
drastically increase suffering and death.



ALTERATIONS OF THE GLOBAL ENVIRONMENT

A nuclear war would involve such prodigious and concentrated short term
release of high temperature energy that it is necessary to consider a
variety of potential environmental effects.

It is true that the energy of nuclear weapons is dwarfed by many
natural phenomena.  A large hurricane may have the power of a million
hydrogen bombs.  But the energy release of even the most severe weather
is diffuse; it occurs over wide areas, and the difference in
temperature between the storm system and the surrounding atmosphere is
relatively small.  Nuclear detonations are just the opposite--highly
concentrated with reaction temperatures up to tens of millions of
degrees Fahrenheit.  Because they are so different from natural
processes, it is necessary to examine their potential for altering the
environment in several contexts.


A.  High Altitude Dust

It has been estimated that a 10,000-megaton war with half the weapons
exploding at ground level would tear up some 25 billion cubic meters of
rock and soil, injecting a substantial amount of fine dust and
particles into the stratosphere.  This is roughly twice the volume of
material blasted loose by the Indonesian volcano, Krakatoa, whose
explosion in 1883 was the most powerful terrestrial event ever
recorded.  Sunsets around the world were noticeably reddened for
several years after the Krakatoa eruption, indicating that large
amounts of volcanic dust had entered the stratosphere.

Subsequent studies of large volcanic explosions, such as Mt. Agung on
Bali in 1963, have raised the possibility that large-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 the solar radiation reaching the
upper stratosphere.

The mechanism for the production of ozone is the absorption by oxygen
molecules (O2) of relatively short-wavelength ultraviolet light.  The
oxygen molecule separates into two atoms of free oxygen, which
immediately unite with other oxygen molecules on the surfaces of
particles in the upper atmosphere.  It is this union which forms ozone,
or O3.  The heat released by the ozone-forming process is the reason
for the curious increase with altitude of the temperature of the
stratosphere (the base of which is about 36,000 feet above the earth's
surface).

While the natural chemical reaction produces about 4,500 tons of ozone
per second in the stratosphere, this is offset by other natural
chemical reactions which break down the ozone.  By far the most
significant involves nitric oxide (NO) which breaks ozone (O3) into
molecules.  This effect was discovered only in the last few years in
studies of the environmental problems which might be encountered if
large fleets of supersonic transport aircraft operate routinely in the
lower stratosphere.  According to a report by Dr. Harold S. Johnston,
University of California at Berkeley--prepared for the Department of
Transportation's Climatic Impact Assessment Program--it now appears
that the NO reaction is normally responsible for 50 to 70 percent of
the destruction of ozone.

In the natural environment, there is a variety of means for the
production of NO and its transport into the stratosphere.  Soil
bacteria produce nitrous oxide (N2O) which enters the lower atmosphere
and slowly diffuses into the stratosphere, where it reacts with free
oxygen (O) to form two NO molecules.  Another mechanism for NO
production in the lower atmosphere may be lightning discharges, and
while NO is quickly washed out of the lower atmosphere by rain, some of
it may reach the stratosphere.  Additional amounts of NO are produced
directly in the stratosphere by cosmic rays from the sun and
interstellar sources.

It is because of this catalytic role which nitric oxide plays in the
destruction of ozone that it is important to consider the effects of
high-yield nuclear explosions on the ozone layer.  The nuclear fireball
and the air entrained within it are subjected to great heat, followed
by relatively rapid cooling.  These conditions are ideal for the
production of tremendous amounts of NO from the air.  It has been
estimated that as much as 5,000 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 problems of large-scale nuclear war from the
standpoint of the countries not under direct attack, and the
difficulties they might encounter in postwar recovery.  It is true that
most of the horror and tragedy of nuclear war would be visited on the
populations subject to direct attack, who would doubtless have to cope
with extreme and perhaps insuperable obstacles in seeking to
reestablish their own societies.  It is no less apparent, however, that
other nations, including those remote from the combat, could suffer
heavily because of damage to the global environment.

Finally, at least brief mention should be made of the global effects
resulting from disruption of economic activities and communications.
Since 1970, an increasing fraction of the human race has been losing
the battle for self-sufficiency in food, and must rely on heavy
imports.  A major disruption of agriculture and transportation in the
grain-exporting and manufacturing countries could thus prove disastrous
to countries importing food, farm machinery, and
fertilizers--especially those which are already struggling with the
threat of widespread starvation.  Moreover, virtually every economic
area, from food and medicines to fuel and growth engendering
industries, the less-developed countries would find they could not rely
on the "undamaged" remainder of the developed world for trade
essentials: in the wake of a nuclear war the industrial powers directly
involved would themselves have to compete for resources with those
countries that today are described as "less-developed."

Similarly, the disruption of international communications--satellites,
cables, and even high frequency radio links--could be a major obstacle
to international recovery efforts.

In attempting to project the after-effects of a major nuclear war, we
have considered separately the various kinds of damage that could
occur.  It is also quite possible, however, that interactions might
take place among these effects, so that one type of damage would couple
with another to produce new and unexpected hazards.  For example, we
can assess individually the consequences of heavy worldwide radiation
fallout and increased solar ultraviolet, but we do not know whether the
two acting together might significantly increase human, animal, or
plant susceptibility to disease.  We can conclude that massive dust
injection into the stratosphere, even greater in scale than Krakatoa,
is unlikely by itself to produce significant climatic and environmental
change, but we cannot rule out interactions with other phenomena, such
as ozone depletion, which might produce utterly unexpected results.

We have come to realize that nuclear weapons can be as unpredictable as
they are deadly in their effects.  Despite some 30 years of development
and study, there is still much that we do not know.  This is
particularly true when we consider the global effects of a large-scale
nuclear war.



Note 1:  Nuclear Weapons Yield

The most widely used standard for measuring the power of nuclear
weapons is "yield," expressed as the quantity of chemical explosive
(TNT) that would produce the same energy release.  The first atomic
weapon which leveled Hiroshima in 1945, had a yield of 13 kilotons;
that is, the explosive power of 13,000 tons of TNT.  (The largest
conventional bomb dropped in World War II contained about 10 tons of
TNT.)

Since Hiroshima, the yields or explosive power of nuclear weapons have
vastly increased.  The world's largest nuclear detonation, set off in
1962 by the Soviet Union, had a yield of 58 megatons--equivalent to 58
million tons of TNT.  A modern ballistic missile may carry warhead
yields up to 20 or more megatons.

Even the most violent wars of recent history have been relatively
limited in terms of the total destructive power of the non-nuclear
weapons used. A single aircraft or ballistic missile today can carry a
nuclear explosive force surpassing that of all the non-nuclear bombs
used in recent wars. The number of nuclear bombs and missiles the
superpowers now possess runs into the thousands.



Note 2:  Nuclear Weapons Design

Nuclear weapons depend on two fundamentally different types of nuclear
reactions, each of which releases energy:

Fission, which involves the splitting of heavy elements (e.g. uranium);
and fusion, which involves the combining of light elements (e.g.
hydrogen).

Fission requires that a minimum amount of material or "critical mass"
be brought together in contact for the nuclear explosion to take place.
The more efficient fission weapons tend to fall in the yield range of
tens of kilotons.  Higher explosive yields become increasingly complex
and impractical.

Nuclear fusion permits the design of weapons of virtually limitless
power. In fusion, according to nuclear theory, when the nuclei of light
atoms like hydrogen are joined, the mass of the fused nucleus is
lighter than the two original nuclei; the loss is expressed as energy.
By the 1930's, physicists had concluded that this was the process which
powered the sun and stars; but the nuclear fusion process remained only
of theoretical interest until it was discovered that an atomic fission
bomb might be used as a "trigger" to produce, within one- or
two-millionths of a second, the intense pressure and temperature
necessary to set off the fusion reaction.

Fusion permits the design of weapons of almost limitless power, using
materials that are far less costly.



Note 3: Radioactivity

Most familiar natural elements like hydrogen, oxygen, gold, and lead
are stable, and enduring unless acted upon by outside forces.  But
almost all elements can exist in unstable forms.  The nuclei of these
unstable "isotopes," as they are called, are "uncomfortable" with the
particular mixture of nuclear particles comprising them, and they
decrease this internal stress through the process of radioactive decay.

The three basic modes of radioactive decay are the emission of alpha,
beta and gamma radiation:

Alpha--Unstable nuclei frequently emit alpha particles, actually helium
nuclei consisting of two protons and two neutrons.  By far the most
massive of the decay particles, it is also the slowest, rarely
exceeding one-tenth the velocity of light.  As a result, its
penetrating power is weak, and it can usually be stopped by a piece of
paper.  But if alpha emitters like plutonium are incorporated in the
body, they pose a serious cancer threat.

Beta--Another form of radioactive decay is the emission of a beta
particle, or electron.  The beta particle has only about one
seven-thousandth the mass of the alpha particle, but its velocity is
very much greater, as much as eight-tenths the velocity of light.  As a
result, beta particles can penetrate far more deeply into bodily tissue
and external doses of beta radiation represent a significantly greater
threat than the slower, heavier alpha particles.  Beta-emitting
isotopes are as harmful as alpha emitters if taken up by the body.

Gamma--In some decay processes, the emission is a photon having no mass
at all and traveling at the speed of light.  Radio waves, visible
light, radiant heat, and X-rays are all photons, differing only in the
energy level each carries.  The gamma ray is similar to the X-ray
photon, but far more penetrating (it can traverse several inches of
concrete).  It is capable of doing great damage in the body.

Common to all three types of nuclear decay radiation is their ability
to ionize (i.e., unbalance electrically) the neutral atoms through
which they pass, that is, give them a net electrical charge.  The alpha
particle, carrying a positive electrical charge, pulls electrons from
the atoms through which it passes, while negatively charged beta
particles can push electrons out of neutral atoms.  If energetic betas
pass sufficiently close to atomic nuclei, they can produce X-rays which
themselves can ionize additional neutral atoms.  Massless but energetic
gamma rays can knock electrons out of neutral atoms in the same fashion
as X-rays, leaving them ionized.  A single particle of radiation can
ionize hundreds of neutral atoms in the tissue in multiple collisions
before all its energy is absorbed.  This disrupts the chemical bonds
for critically important cell structures like the cytoplasm, which
carries the cell's genetic blueprints, and also produces chemical
constituents which can cause as much damage as the original ionizing
radiation.

For convenience, a unit of radiation dose called the "rad" has been
adopted.  It measures the amount of ionization produced per unit volume
by the particles from radioactive decay.



Note 4: Nuclear Half-Life

The concept of "half-life" is basic to an understanding of radioactive
decay of unstable nuclei.

Unlike physical "systems"--bacteria, animals, men and stars--unstable
isotopes do not individually have a predictable life span.  There is no
way of forecasting when a single unstable nucleus will decay.

Nevertheless, it is possible to get around the random behavior of an
individual nucleus by dealing statistically with large numbers of
nuclei of a particular radioactive isotope.  In the case of
thorium-232, for example, radioactive decay proceeds so slowly that 14
billion years must elapse before one-half of an initial quantity
decayed to a more stable configuration.  Thus the half-life of this
isotope is 14 billion years. After the elapse of second half-life
(another 14 billion years), only one-fourth of the original quantity of
thorium-232 would remain, one eighth after the third half-life, and so
on.

Most manmade radioactive isotopes have much shorter half-lives, ranging
from seconds or days up to thousands of years.  Plutonium-239 (a
manmade isotope) has a half-life of 24,000 years.

For the most common uranium isotope, U-238, the half-life is 4.5
billion years, about the age of the solar system.  The much scarcer,
fissionable isotope of uranium, U-235, has a half-life of 700 million
years, indicating that its present abundance is only about 1 percent of
the amount present when the solar system was born.



Note 5: Oxygen, Ozone and Ultraviolet Radiation

Oxygen, vital to breathing creatures, constitutes about one-fifth of
the earth's atmosphere.  It occasionally occurs as a single atom in the
atmosphere at high temperature, but it usually combines with a second
oxygen atom to form molecular oxygen (O2).  The oxygen in the air we
breathe consists primarily of this stable form.

Oxygen has also a third chemical form in which three oxygen atoms are
bound together in a single molecule (03), called ozone.  Though less
stable and far more rare than O2, and principally confined to upper
levels of the stratosphere, both molecular oxygen and ozone play a
vital role in shielding the earth from harmful components of solar
radiation.

Most harmful radiation is in the "ultraviolet" region of the solar
spectrum, invisible to the eye at short wavelengths (under 3,000 A).
(An angstrom unit--A--is an exceedingly short unit of length--10
billionths of a centimeter, or about 4 billionths of an inch.) Unlike
X-rays, ultraviolet photons are not "hard" enough to ionize atoms, but
pack enough energy to break down the chemical bonds of molecules in
living cells and produce a variety of biological and genetic
abnormalities, including tumors and cancers.

Fortunately, because of the earth's atmosphere, only a trace of this
dangerous ultraviolet radiation actually reaches the earth.  By the
time sunlight reaches the top of the stratosphere, at about 30 miles
altitude, almost all the radiation shorter than 1,900 A has been
absorbed by molecules of nitrogen and oxygen.  Within the stratosphere
itself, molecular oxygen (02) absorbs the longer wavelengths of
ultraviolet, up to 2,420 A; and ozone (O3) is formed as a result of
this absorption process. It is this ozone then which absorbs almost all
of the remaining ultraviolet wavelengths up to about 3,000 A, so that
almost all of the dangerous solar radiation is cut off before it
reaches the earth's surface.