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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. Butstudies have been concerned for the most part with those immediateconsequences which would be suffered by a country that was the directtarget of nuclear attack. Relatively few studies have examined theworldwide, long term effects. 

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

New discoveries have been made, yet much uncertainty inevitablypersists. Our knowledge of nuclear warfare rests largely on theory andhypothesis, fortunately untested by the usual processes of trial anderror; the paramount goal of statesmanship is that we should neverlearn from the experience of nuclear war. 

The uncertainties that remain are of such magnitude that of themselvesthey must serve as a further deterrent to the use of nuclear weapons. At the same time, knowledge, even fragmentary knowledge, of the broadereffects of nuclear weapons underlines the extreme difficulty thatstrategic planners of any nation would face in attempting to predictthe results of a nuclear war. Uncertainty is one of the majorconclusions in our studies, as the haphazard and unpredicted derivationof many of our discoveries emphasizes. Moreover, it now appears that amassive attack with many large-scale nuclear detonations could causesuch widespread and long-lasting environmental damage that theaggressor country might suffer serious physiological, economic, andenvironmental effects even without a nuclear response by the countryattacked. 

An effort has been made to present this paper in language that does notrequire a scientific background on the part of the reader. Nevertheless it must deal in schematized processes, abstractions, andstatistical generalizations. Hence one supremely important perspectivemust be largely supplied by the reader: the human perspective--themeaning of these physical effects for individual human beings and forthe 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 thermonuclearfusion weapons into the military inventories of the great powers, andmore than a decade since the United States, Great Britain, and theSoviet Union ceased to test nuclear weapons in the atmosphere. Todayour understanding of the technology of thermonuclear weapons seemshighly advanced, but our knowledge of the physical and biologicalconsequences of nuclear war is continuously evolving. 

Only recently, new light was shed on the subject in a study which theArms Control and Disarmament Agency had asked the National Academy ofSciences to undertake. Previous studies had tended to focus verylargely on radioactive fallout from a nuclear war; an important aspectof this new study was its inquiry into all possible consequences, including the effects of large-scale nuclear detonations on the ozonelayer which helps protect life on earth from the sun's ultravioletradiations. Assuming a total detonation of 10, 000 megatons--alarge-scale but less than total nuclear "exchange, " as one would say inthe dehumanizing jargon of the strategists--it was concluded that asmuch as 30-70 percent of the ozone might be eliminated from thenorthern hemisphere (where a nuclear war would presumably take place)and as much as 20-40 percent from the southern hemisphere. Recoverywould probably take about 3-10 years, but the Academy's study notesthat long term global changes cannot be completely ruled out. 

The reduced ozone concentrations would have a number of consequencesoutside the areas in which the detonations occurred. The Academy studynotes, for example, that the resultant increase in ultraviolet wouldcause "prompt incapacitating cases of sunburn in the temperate zonesand snow blindness in northern countries . . . "

Strange though it might seem, the increased ultraviolet radiation couldalso be accompanied by a drop in the average temperature. The size ofthe change is open to question, but the largest changes would probablyoccur at the higher latitudes, where crop production and ecologicalbalances are sensitively dependent on the number of frost-free days andother factors related to average temperature. The Academy's studyconcluded that ozone changes due to nuclear war might decrease globalsurface temperatures by only negligible amounts or by as much as a fewdegrees. To calibrate the significance of this, the study mentionedthat a cooling of even 1 degree centigrade would eliminate commercialwheat growing in Canada. 

Thus, the possibility of a serious increase in ultraviolet radiationhas been added to widespread radioactive fallout as a fearsomeconsequence of the large-scale use of nuclear weapons. And it islikely that we must reckon with still other complex and subtleprocesses, global in scope, which could seriously threaten the healthof distant populations in the event of an all-out nuclear war. 

Up to now, many of the important discoveries about nuclear weaponeffects have been made not through deliberate scientific inquiry but byaccident. And as the following historical examples show, there has beena series of surprises. 

"Castle/Bravo" was the largest nuclear weapon ever detonated by theUnited States. Before it was set off at Bikini on February 28, 1954, it was expected to explode with an energy equivalent of about 8 milliontons of TNT. Actually, it produced almost twice that explosivepower--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 sprinklethe Japanese fishing vessel Lucky Dragon, some 90 miles downwind of theburst point, and Rongelap Atoll, 100 miles downwind. Though 40 to 50miles away from the proscribed test area, the vessel's crew and theislanders received heavy doses of radiation from the weapon's"fallout"--the coral rock, soil, and other debris sucked up in thefireball and made intensively radioactive by the nuclear reaction. Oneradioactive isotope in the fallout, iodine-131, rapidly built up toserious concentration in the thyroid glands of the victims, particularly young Rongelapese children. 

More than any other event in the decade of testing large nuclearweapons in the atmosphere, Castle/Bravo's unexpected contamination of7, 000 square miles of the Pacific Ocean dramatically illustrated howlarge-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 nuclearweapons development. For example, what was probably man's mostextensive modification of the global environment to date occurred inSeptember 1962, when a nuclear device was detonated 250 miles aboveJohnson Island. The 1. 4-megaton burst produced an artificial belt ofcharged particles trapped in the earth's magnetic field. Though 98percent of these particles were removed by natural processes after thefirst year, traces could be detected 6 or 7 years later. A number ofsatellites in low earth orbit at the time of the burst suffered severeelectronic damage resulting in malfunctions and early failure. Itbecame obvious that man now had the power to make long term changes inhis near-space environment. 

Another unexpected effect of high-altitude bursts was the blackout ofhigh-frequency radio communications. Disruption of the ionosphere(which reflects radio signals back to the earth) by nuclear bursts overthe Pacific has wiped out long-distance radio communications for hoursat distances of up to 600 miles from the burst point. 

Yet another surprise was the discovery that electromagnetic pulses canplay havoc with electrical equipment itself, including some in commandsystems that control the nuclear arms themselves. 

Much of our knowledge was thus gained by chance--a fact which shouldimbue us with humility as we contemplate the remaining uncertainties(as well as the certainties) about nuclear warfare. What we havelearned enables us, nonetheless, to see more clearly. We know, forinstance, that some of the earlier speculations about the after-effectsof a global nuclear war were as far-fetched as they werehorrifying--such as the idea that the worldwide accumulation ofradioactive fallout would eliminate all life on the planet, or that itmight produce a train of monstrous genetic mutations in all livingthings, making future life unrecognizable. And this accumulation ofknowledge which enables us to rule out the more fanciful possibilitiesalso allows us to reexamine, with some scientific rigor, otherphenomena which could seriously affect the global environment and thepopulations of participant and nonparticipant countries alike. 

This paper is an attempt to set in perspective some of the longer termeffects of nuclear war on the global environment, with emphasis onareas 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 inless than one millionth of a second. Most of this is in the form ofthe heat and shock waves which produce the damage. It is thisimmediate and direct explosive power which could devastate the urbancenters in a major nuclear war. 

Compared with the immediate colossal destruction suffered in targetareas, the more subtle, longer term effects of the remaining 10 percentof the energy released by nuclear weapons might seem a matter ofsecondary concern. But the dimensions of the initial catastropheshould not overshadow the after-effects of a nuclear war. They wouldbe global, affecting nations remote from the fighting for many yearsafter the holocaust, because of the way nuclear explosions behave inthe atmosphere and the radioactive products released by nuclear bursts. 

When a weapon is detonated at the surface of the earth or at lowaltitudes, the heat pulse vaporizes the bomb material, target, nearbystructures, and underlying soil and rock, all of which become entrainedin an expanding, fast-rising fireball. As the fireball rises, itexpands and cools, producing the distinctive mushroom cloud, signatureof nuclear explosions. 

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

RADIOACTIVE FALLOUT

Both the local and worldwide fallout hazards of nuclear explosionsdepend on a variety of interacting factors: weapon design, explosiveforce, altitude and latitude of detonation, time of year, and localweather conditions. 

All present nuclear weapon designs require the splitting of heavyelements like uranium and plutonium. The energy released in thisfission process is many millions of times greater, pound for pound, than the most energetic chemical reactions. The smaller nuclearweapon, in the low-kiloton range, may rely solely on the energyreleased by the fission process, as did the first bombs whichdevastated Hiroshima and Nagasaki in 1945. The larger yield nuclearweapons derive a substantial part of their explosive force from thefusion of heavy forms of hydrogen--deuterium and tritium. Since thereis virtually no limitation on the volume of fusion materials in aweapon, and the materials are less costly than fissionable materials, the fusion, "thermonuclear, " or "hydrogen" bomb brought a radicalincrease in the explosive power of weapons. However, the fissionprocess is still necessary to achieve the high temperatures andpressures needed to trigger the hydrogen fusion reactions. Thus, allnuclear detonations produce radioactive fragments of heavy elementsfission, with the larger bursts producing an additional radiationcomponent from the fusion process. 

The nuclear fragments of heavy-element fission which are of greatestconcern are those radioactive atoms (also called radionuclides) whichdecay by emitting energetic electrons or gamma particles. (See"Radioactivity" note. ) An important characteristic here is the rate ofdecay. This is measured in terms of "half-life"--the time required forone-half of the original substance to decay--which ranges from days tothousands of years for the bomb-produced radionuclides of principalinterest. (See "Nuclear Half-Life" note. ) Another factor which iscritical in determining the hazard of radionuclides is the chemistry ofthe atoms. This determines whether they will be taken up by the bodythrough respiration or the food cycle and incorporated into tissue. Ifthis occurs, the risk of biological damage from the destructiveionizing radiation (see "Radioactivity" note) is multiplied. 

Probably the most serious threat is cesium-137, a gamma emitter with ahalf-life of 30 years. It is a major source of radiation in nuclearfallout, and since it parallels potassium chemistry, it is readilytaken into the blood of animals and men and may be incorporated intotissue. 

Other hazards are strontium-90, an electron emitter with a half-life of28 years, and iodine-131 with a half-life of only 8 days. Strontium-90follows calcium chemistry, so that it is readily incorporated into thebones and teeth, particularly of young children who have received milkfrom cows consuming contaminated forage. Iodine-131 is a similarthreat to infants and children because of its concentration in thethyroid gland. In addition, there is plutonium-239, frequently used innuclear explosives. A bone-seeker like strontium-90, it may also becomelodged in the lungs, where its intense local radiation can cause canceror other damage. Plutonium-239 decays through emission of an alphaparticle (helium nucleus) and has a half-life of 24, 000 years. 

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

Three types of radiation damage may occur: bodily damage (mainlyleukemia and cancers of the thyroid, lung, breast, bone, andgastrointestinal tract); genetic damage (birth defects andconstitutional and degenerative diseases due to gonodal damage sufferedby parents); and development and growth damage (primarily growth andmental retardation of unborn infants and young children). Since heavyradiation doses of about 20 roentgen or more (see "Radioactivity" note)are necessary to produce developmental defects, these effects wouldprobably be confined to areas of heavy local fallout in the nuclearcombatant nations and would not become a global problem. 

A. Local Fallout

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

It has been estimated that a weapon with a fission yield of 1 milliontons TNT equivalent power (1 megaton) exploded at ground level in a 15miles-per-hour wind would produce fallout in an ellipse extendinghundreds of miles downwind from the burst point. At a distance of20-25 miles downwind, a lethal radiation dose (600 rads) would beaccumulated by a person who did not find shelter within 25 minutesafter the time the fallout began. At a distance of 40-45 miles, aperson would have at most 3 hours after the fallout began to findshelter. Considerably smaller radiation doses will make peopleseriously ill. Thus, the survival prospects of persons immediatelydownwind of the burst point would be slim unless they could besheltered or evacuated. 

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

Most of the bomb-produced radionuclides decay rapidly. Even so, beyondthe blast radius of the exploding weapons there would be areas ("hotspots") the survivors could not enter because of radioactivecontamination from long-lived radioactive isotopes like strontium-90 orcesium-137, which can be concentrated through the food chain andincorporated into the body. The damage caused would be internal, withthe injurious effects appearing over many years. For the survivors ofa nuclear war, this lingering radiation hazard could represent a gravethreat 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 ofradionuclides has been derived from the period of intensive nucleartesting in the atmosphere during the 1950's and early 1960's. It isestimated that more than 500 megatons of nuclear yield were detonatedin the atmosphere between 1945 and 1971, about half of this yield beingproduced by a fission reaction. The peak occurred in 1961-62, when atotal of 340 megatons were detonated in the atmosphere by the UnitedStates and Soviet Union. The limited nuclear test ban treaty of 1963ended atmospheric testing for the United States, Britain, and theSoviet 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 percapita dose to the world's population up to the year 2000 as a resultof atmospheric testing through 1970 (cutoff date of the study) will bethe equivalent of 2 years' exposure to natural background radiation onthe earth's surface. For the bulk of the world's population, internaland external radiation doses of natural origin amount to less thanone-tenth rad annually. Thus nuclear testing to date does not appearto pose a severe radiation threat in global terms. But a nuclear warreleasing 10 or 100 times the total yield of all previous weapons testscould pose a far greater worldwide threat. 

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

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

ALTERATIONS OF THE GLOBAL ENVIRONMENT

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

It is true that the energy of nuclear weapons is dwarfed by manynatural phenomena. A large hurricane may have the power of a millionhydrogen bombs. But the energy release of even the most severe weatheris diffuse; it occurs over wide areas, and the difference intemperature between the storm system and the surrounding atmosphere isrelatively small. Nuclear detonations are just the opposite--highlyconcentrated with reaction temperatures up to tens of millions ofdegrees Fahrenheit. Because they are so different from naturalprocesses, it is necessary to examine their potential for altering theenvironment in several contexts. 

A. High Altitude Dust

It has been estimated that a 10, 000-megaton war with half the weaponsexploding at ground level would tear up some 25 billion cubic meters ofrock and soil, injecting a substantial amount of fine dust andparticles into the stratosphere. This is roughly twice the volume ofmaterial blasted loose by the Indonesian volcano, Krakatoa, whoseexplosion in 1883 was the most powerful terrestrial event everrecorded. Sunsets around the world were noticeably reddened forseveral years after the Krakatoa eruption, indicating that largeamounts of volcanic dust had entered the stratosphere. 

Subsequent studies of large volcanic explosions, such as Mt. Agung onBali in 1963, have raised the possibility that large-scale injection ofdust into the stratosphere would reduce sunlight intensities andtemperatures at the surface, while increasing the absorption of heat inthe upper atmosphere. 

The resultant minor changes in temperature and sunlight could affectcrop production. However, no catastrophic worldwide changes haveresulted from volcanic explosions, so it is doubtful that the grossinjection of particulates into the stratosphere by a 10, 000-megatonconflict would, by itself, lead to major global climate changes. 

B. Ozone

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

The reason is that while oxygen and nitrogen in the upper reaches ofthe atmosphere can block out solar ultraviolet photons with wavelengthsshorter than 2, 420 angstroms (A), ozone is the only effective shield inthe atmosphere against solar ultraviolet radiation between 2, 500 and3, 000 A in wavelength. (See note 5. ) Although ozone is extremelyefficient at filtering out solar ultraviolet in 2, 500-3, 000 A region ofthe 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 havesince found that intense ultraviolet radiation can inhibitphotosynthesis 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 liveableenvironment at the earth's surface, the total quantity of ozone in theatmosphere is quite small, only about 3 parts per million. Furthermore, ozone is not a durable or static constituent of theatmosphere. It is constantly created, destroyed, and recreated bynatural processes, so that the amount of ozone present at any giventime is a function of the equilibrium reached between the creative anddestructive chemical reactions and the solar radiation reaching theupper stratosphere. 

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

While the natural chemical reaction produces about 4, 500 tons of ozoneper second in the stratosphere, this is offset by other naturalchemical reactions which break down the ozone. By far the mostsignificant involves nitric oxide (NO) which breaks ozone (O3) intomolecules. This effect was discovered only in the last few years instudies of the environmental problems which might be encountered iflarge fleets of supersonic transport aircraft operate routinely in thelower stratosphere. According to a report by Dr. Harold S. Johnston, University of California at Berkeley--prepared for the Department ofTransportation's Climatic Impact Assessment Program--it now appearsthat the NO reaction is normally responsible for 50 to 70 percent ofthe destruction of ozone. 

In the natural environment, there is a variety of means for theproduction of NO and its transport into the stratosphere. Soilbacteria produce nitrous oxide (N2O) which enters the lower atmosphereand slowly diffuses into the stratosphere, where it reacts with freeoxygen (O) to form two NO molecules. Another mechanism for NOproduction in the lower atmosphere may be lightning discharges, andwhile NO is quickly washed out of the lower atmosphere by rain, some ofit may reach the stratosphere. Additional amounts of NO are produceddirectly in the stratosphere by cosmic rays from the sun andinterstellar sources. 

It is because of this catalytic role which nitric oxide plays in thedestruction of ozone that it is important to consider the effects ofhigh-yield nuclear explosions on the ozone layer. The nuclear fireballand the air entrained within it are subjected to great heat, followedby relatively rapid cooling. These conditions are ideal for theproduction of tremendous amounts of NO from the air. It has beenestimated that as much as 5, 000 tons of nitric oxide is produced foreach megaton of nuclear explosive power. 

What would be the effects of nitric oxides driven into the stratosphereby an all-out nuclear war, involving the detonation of 10, 000 megatonsof explosive force in the northern hemisphere? According to the recentNational Academy of Sciences study, the nitric oxide produced by theweapons could reduce the ozone levels in the northern hemisphere by asmuch as 30 to 70 percent. 

To begin with, a depleted ozone layer would reflect back to the earth'ssurface less heat than would normally be the case, thus causing a dropin temperature--perhaps enough to produce serious effects onagriculture. Other changes, such as increased amounts of dust ordifferent vegetation, might subsequently reverse this drop intemperature--but on the other hand, it might increase it. 

Probably more important, life on earth has largely evolved within theprotective ozone shield and is presently adapted rather precisely tothe amount of solar ultraviolet which does get through. To defendthemselves against this low level of ultraviolet, evolved externalshielding (feathers, fur, cuticular waxes on fruit), internal shielding(melanin pigment in human skin, flavenoids in plant tissue), avoidancestrategies (plankton migration to greater depths in the daytime, shade-seeking by desert iguanas) and, in almost all organisms butplacental mammals, elaborate mechanisms to repair photochemical damage. 

It is possible, however, that a major increase in solar ultravioletmight overwhelm the defenses of some and perhaps many terrestrial lifeforms. Both direct and indirect damage would then occur among thebacteria, insects, plants, and other links in the ecosystems on whichhuman well-being depends. This disruption, particularly if it occurredin the aftermath of a major war involving many other dislocations, could pose a serious additional threat to the recovery of postwarsociety. The National Academy of Sciences report concludes that in 20years the ecological systems would have essentially recovered from theincrease in ultraviolet radiation--though not necessarily fromradioactivity or other damage in areas close to the war zone. However, a delayed effect of the increase in ultraviolet radiation would be anestimated 3 to 30 percent increase in skin cancer for 40 years in theNorthern Hemisphere's mid-latitudes. 

SOME CONCLUSIONS

We have considered the problems of large-scale nuclear war from thestandpoint of the countries not under direct attack, and thedifficulties they might encounter in postwar recovery. It is true thatmost of the horror and tragedy of nuclear war would be visited on thepopulations subject to direct attack, who would doubtless have to copewith extreme and perhaps insuperable obstacles in seeking toreestablish their own societies. It is no less apparent, however, thatother nations, including those remote from the combat, could sufferheavily because of damage to the global environment. 

Finally, at least brief mention should be made of the global effectsresulting from disruption of economic activities and communications. Since 1970, an increasing fraction of the human race has been losingthe battle for self-sufficiency in food, and must rely on heavyimports. A major disruption of agriculture and transportation in thegrain-exporting and manufacturing countries could thus prove disastrousto countries importing food, farm machinery, andfertilizers--especially those which are already struggling with thethreat of widespread starvation. Moreover, virtually every economicarea, from food and medicines to fuel and growth engenderingindustries, the less-developed countries would find they could not relyon the "undamaged" remainder of the developed world for tradeessentials: in the wake of a nuclear war the industrial powers directlyinvolved would themselves have to compete for resources with thosecountries 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 obstacleto international recovery efforts. 

In attempting to project the after-effects of a major nuclear war, wehave considered separately the various kinds of damage that couldoccur. It is also quite possible, however, that interactions mighttake place among these effects, so that one type of damage would couplewith another to produce new and unexpected hazards. For example, wecan assess individually the consequences of heavy worldwide radiationfallout and increased solar ultraviolet, but we do not know whether thetwo acting together might significantly increase human, animal, orplant susceptibility to disease. We can conclude that massive dustinjection into the stratosphere, even greater in scale than Krakatoa, is unlikely by itself to produce significant climatic and environmentalchange, but we cannot rule out interactions with other phenomena, suchas ozone depletion, which might produce utterly unexpected results. 

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

Note 1: Nuclear Weapons Yield

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

Since Hiroshima, the yields or explosive power of nuclear weapons havevastly increased. The world's largest nuclear detonation, set off in1962 by the Soviet Union, had a yield of 58 megatons--equivalent to 58million tons of TNT. A modern ballistic missile may carry warheadyields up to 20 or more megatons. 

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

Note 2: Nuclear Weapons Design

Nuclear weapons depend on two fundamentally different types of nuclearreactions, 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 oftens of kilotons. Higher explosive yields become increasingly complexand impractical. 

Nuclear fusion permits the design of weapons of virtually limitlesspower. In fusion, according to nuclear theory, when the nuclei of lightatoms like hydrogen are joined, the mass of the fused nucleus islighter than the two original nuclei; the loss is expressed as energy. By the 1930's, physicists had concluded that this was the process whichpowered the sun and stars; but the nuclear fusion process remained onlyof theoretical interest until it was discovered that an atomic fissionbomb might be used as a "trigger" to produce, within one- ortwo-millionths of a second, the intense pressure and temperaturenecessary to set off the fusion reaction. 

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

Note 3: Radioactivity

Most familiar natural elements like hydrogen, oxygen, gold, and leadare stable, and enduring unless acted upon by outside forces. Butalmost all elements can exist in unstable forms. The nuclei of theseunstable "isotopes, " as they are called, are "uncomfortable" with theparticular mixture of nuclear particles comprising them, and theydecrease 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 heliumnuclei consisting of two protons and two neutrons. By far the mostmassive of the decay particles, it is also the slowest, rarelyexceeding one-tenth the velocity of light. As a result, itspenetrating power is weak, and it can usually be stopped by a piece ofpaper. But if alpha emitters like plutonium are incorporated in thebody, they pose a serious cancer threat. 

Beta--Another form of radioactive decay is the emission of a betaparticle, or electron. The beta particle has only about oneseven-thousandth the mass of the alpha particle, but its velocity isvery much greater, as much as eight-tenths the velocity of light. As aresult, beta particles can penetrate far more deeply into bodily tissueand external doses of beta radiation represent a significantly greaterthreat than the slower, heavier alpha particles. Beta-emittingisotopes are as harmful as alpha emitters if taken up by the body. 

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

Common to all three types of nuclear decay radiation is their abilityto ionize (i. E. , unbalance electrically) the neutral atoms throughwhich they pass, that is, give them a net electrical charge. The alphaparticle, carrying a positive electrical charge, pulls electrons fromthe atoms through which it passes, while negatively charged betaparticles can push electrons out of neutral atoms. If energetic betaspass sufficiently close to atomic nuclei, they can produce X-rays whichthemselves can ionize additional neutral atoms. Massless but energeticgamma rays can knock electrons out of neutral atoms in the same fashionas X-rays, leaving them ionized. A single particle of radiation canionize hundreds of neutral atoms in the tissue in multiple collisionsbefore all its energy is absorbed. This disrupts the chemical bondsfor critically important cell structures like the cytoplasm, whichcarries the cell's genetic blueprints, and also produces chemicalconstituents which can cause as much damage as the original ionizingradiation. 

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

Note 4: Nuclear Half-Life

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

Unlike physical "systems"--bacteria, animals, men and stars--unstableisotopes do not individually have a predictable life span. There is noway of forecasting when a single unstable nucleus will decay. 

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

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

For the most common uranium isotope, U-238, the half-life is 4. 5billion years, about the age of the solar system. The much scarcer, fissionable isotope of uranium, U-235, has a half-life of 700 millionyears, indicating that its present abundance is only about 1 percent ofthe amount present when the solar system was born. 

Note 5: Oxygen, Ozone and Ultraviolet Radiation

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

Oxygen has also a third chemical form in which three oxygen atoms arebound together in a single molecule (03), called ozone. Though lessstable and far more rare than O2, and principally confined to upperlevels of the stratosphere, both molecular oxygen and ozone play avital role in shielding the earth from harmful components of solarradiation. 

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

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