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- Some Perspectives


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Worldwide Effects of Nuclear War - - - Some Perspectives

by the U.S. Arms Control and Disarmament Agency.

October, 1996  [Etext #684]


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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,OOO 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. 




End of the Project Gutenberg Etext of Worldwide Effects of Nuclear War