Worldwide Effects of Nuclear War Some Perspectives
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the U.S. Arms Control and Disarmament Agency. >> Worldwide Effects of Nuclear War Some Perspectives
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.