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Home , Doomsday Clock, Emil Konopinski, Global catastrophic risk, Nuclear holocaust, Nuclear torpedo, Nuclear winter

NUCLEAR WAR AS A GLOBAL CATASTROPHIC

National Security Report

James Scouras

NUCLEAR WAR AS A

James Scouras Copyright © 2020 The Johns Hopkins University Applied Laboratory LLC.

This paper was first published in the Journal of Benefit-Cost Analysis 10, no. 2 (2019): 274–295, doi:10.1017/ bca.2019.16, © Society for Benefit-Cost Analysis, 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. In addition to stylistic changes and minor text updates, the following changes have been made in this version: • ’s estimate noted in the text was corrected from 2 in 1000 and 1 in 1000 to 2 in 1000 and 1 in 100 (see p. 7). Table 1, which includes this estimate, is correct in the original version. • Reference 35 was added (see pp. 10 and 17). • The data sources in Figure 4 were corrected (and now appear in a note below the figure; see p. 11).

NSAD-R-20-015 Nuclear War as a Global Catastrophic Risk iii

Contents

Figures...... v

Tables...... v

Summary...... vii

Why Is Nuclear War a Global Catastrophic Risk?...... 2

Risk Assessment...... 4 Likelihood...... 4 Consequences...... 8

Risk Management...... 10 Nonproliferation...... 10 Counterterrorism...... 10 Deterrence...... 11 Residual Risk and Risk Acceptance...... 15

Final Thoughts and Recommendations...... 16

Bibliography...... 17

About the Author...... 21

Figures Tables

Nuclear War as a Global Catastrophic Risk v

Figures

Figure 1. images of Devastation Caused by Nuclear War...... 2

Figure 2. the Lugar Survey, Question 5...... 5

Figure 3. the , 1947–2004...... 6

Figure 4. uS and Soviet/Russian Nuclear Arsenals over Time...... 11

Figure 5. uncertainty in the Probability of Winning a Nuclear Crisis...... 12

Figure 6. Measures of Effectiveness for Nuclear ...... 13

Figure 7. Wartime Fatalities as a Percentage of World , as Appears in the 2018 Nuclear Posture Review Report...... 14

Figure 8. recalculated Annual Wartime Fatalities as a Percentage of ...... 15

Tables

Table 1. individual Estimates of the Probability of Nuclear War...... 7

Figure credits: Figure 1. Public domain images via Wikimedia Commons, https://commons.wikimedia.org/wiki/File: Hiroshima_aftermath.jpg and https://commons.wikimedia.org/wiki/File:Nagasaki_-_person_burned.jpg. Figure 3. Public domain image via Wikimedia Commons, https://commons.wikimedia.org/wiki/File: Doomsday_Clock_graph.svg.

Nuclear War as a Global Catastrophic Risk vii

Summary

Nuclear war is clearly a global catastrophic risk, but it is not an existential risk as is sometimes carelessly claimed. Unfortunately, the consequence and likelihood components of the risk of nuclear war are both highly uncertain. In particular, for nuclear wars that include targeting of multiple cities, nuclear may result in more fatalities across the globe than the better-understood effects of blast, prompt radiation, and . effects, which could range from minor electrical disturbances to the complete collapse of the electric grid, are similarly highly uncertain. Nuclear war likelihood assessments are largely based on intuition, and they span the spectrum from zero to certainty. Notwithstanding these profound uncertainties, we must manage the risk of nuclear war with the knowledge we have. Benefit-cost analysis and other structured analytic methods applied to evaluate risk mitigation measures must acknowledge that we often do not even know whether many proposed approaches (e.g., reducing nuclear arsenals) will have a net positive or negative effect. Multidisciplinary studies are needed to better understand the consequences and likelihood of nuclear war and the complex relationship between these two components of risk, and to predict both the direction and magnitude of risk mitigation approaches.

Nuclear War as a Global Catastrophic Risk 1

t might be thought that we know enough about Regarding likelihood, how do we know what the the risk of nuclear war to appropriately manage likelihood of nuclear war is and the degree to which that risk. The consequences of unconstrained our national policies affect that likelihood, for Inuclear attacks, and the counterattacks that would better or worse? How much confidence should we occur until the major nuclear powers exhaust place in any assessment of likelihood? What levels their arsenals, would far exceed any cataclysm of likelihood for the broad spectrum of possible humanity has suffered in all of recorded history. consequences pose unacceptable levels of risk? Even The likelihood of such a war must, therefore, a very low (nondecreasing) annual likelihood of the be reduced as much as possible. But this rather risk of nuclear war would result in near certainty of simplistic logic raises many questions and does not catastrophe over the course of enough years. withstand close scrutiny. Most fundamentally and counterintuitively, are we Regarding consequences, does unconstrained nu- really sure we want to reduce the risk of nuclear clear war pose an existential risk to humanity? The war? The successful operation of deterrence, which consequences of existential are truly incalcu- has been credited—perhaps too generously—with lable, including the lives not only of all human be- preventing nuclear war during the and ings currently living but also of all those yet to its aftermath, depends on the risk that any nuclear come; involving not only Homo sapiens but all spe- use might escalate to a . Many cies that may descend from it. At the opposite end proposals for reducing risk focus on reducing of the spectrum of consequences lies the domain of nuclear arsenals and, therefore, the possible “limited” nuclear wars. Are these also properly con- consequences of the most extreme nuclear war. Yet, sidered global catastrophes? After all, while the if we reduce the consequences of nuclear war, might only nuclear war that has ever occurred devastated we also inadvertently increase its likelihood? It’s and , it was also instrumental not at all clear that would be a desirable trade-off. in bringing about the end of the Pacific War, there- This is all to argue that the simplistic logic described by saving lives that would have been lost in the above is inadequate, even dangerous. A more planned invasion of Japan. Indeed, some scholars nuanced understanding of the risk of nuclear war similarly argue that many lives have been saved is imperative. This paper thus attempts to establish over the nearly three-fourths of a century since the a basis for more rigorously addressing the risk of advent of nuclear weapons because those weapons nuclear war. Rather than trying to assess the risk, a have prevented the large conventional wars that daunting objective, its more modest goals include otherwise would likely have occurred between the increasing the awareness of the complexities major powers. This is perhaps the most significant involved in addressing this topic and evaluating consequence of the attacks that devastated the two alternative measures proposed for managing Japanese cities. nuclear risk.

This paper was first published in theJournal of Benefit-Cost Analysis 10, no. 2 (2019): 274–295, doi:10.1017/bca.2019.16 © Society for Benefit-Cost Analysis, 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited. Changes to this version are described on p. ii of this document. This paper reflects the views of the author, and does not represent an official position of the GW Regulatory Studies Center or the George Washington University. The Center’s policy on research integrity is available athttp://regulatorystudies.columbian.gwu. edu/policy-research-integrity. 2 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

Left, Hiroshima after the atomic bomb attack of August 6, 1945. Right, an atomic bomb victim in Nagasaki, attacked August 9, 1945. Note that the image of Hiroshima was signed by Col. Paul Tibbets, pilot of the Enola Gay, the aircraft used to bomb Hiroshima. Figure 1. Images of Devastation Caused by Nuclear War

I begin with a clarification of why nuclear war is consequences—prompt radiation, fallout, etc.— a global catastrophic risk but not an existential not visible in such photographs. Yet, it is also true risk. Turning to the issue of , I then that not all nuclear wars would be so catastrophic; present a variety of assessments by academics and some, perhaps involving electromagnetic pulse statesmen of the likelihood component of the risk (EMP) attacks1 using only a few high-altitude of nuclear war, followed by an overview of what detonations or demonstration strikes of various we do and do not know about the consequences kinds, could result in few casualties. Others, such as of nuclear war, emphasizing uncertainty in a war between Israel and one of its potential future both factors. Then, I discuss the difficulties nuclear neighbors, might be regionally devastating in determining the effects of risk mitigation but have limited global impact, at least if we limit policies, focusing on nuclear arms reduction. our consideration to direct and immediate physical Finally, I address the question of whether nuclear consequences. Nevertheless, smaller nuclear wars weapons have indeed saved lives. I conclude with need to be included in any analysis of nuclear war as recommendations for national security policy and a global catastrophic risk because they increase the multidisciplinary research. likelihood of larger nuclear wars. This is precisely why the nuclear taboo is so precious and crossing Why Is Nuclear War a Global

Catastrophic Risk? 1 Many mistakenly believe that the congressionally established Commission to Assess the Threat to the United States from One needs only to view the pictures of Hiroshima Electromagnetic Pulse (EMP) Attack concluded that an EMP and Nagasaki shown in Figure 1 and imagine such attack would, indeed, be catastrophic to electronic systems and devastation visited on thousands of cities across consequently to people and societies that vitally depend on warring nations in both hemispheres to recognize those systems. However, the conclusion of the commission, on whose staff I served, was only that such a catastrophe could, not that nuclear war is truly a global catastrophic risk. would, result from an EMP attack. Its executive report states, Moreover, many of today’s nuclear weapons are an for example, that “the damage level could be sufficient to be order of magnitude more destructive than catastrophic to the Nation.” See www.empcommision.org for and , and there are many other significant publicly available reports from the EMP Commission. See also Frankel, Scouras, and DeSimone, Assessing the Risk. Nuclear War as a Global Catastrophic Risk 3 the nuclear threshold into uncharted territory is Beach by Nevil Shute6 and the subsequent 1959 so dangerous.2 movie version.7 The story describes survivors in While it is clear that nuclear war is a global Melbourne, Australia, one of a few remaining catastrophic risk, it is also clear that it is not an human outposts in the Southern Hemisphere, as existential risk. Yet over the course of the clouds approached to bring the final blow age, a series of mechanisms have been proposed to humanity. that, it has been erroneously argued, could lead In the 1970s, after fallout was better understood to to human . The first concern3 arose be limited in space, time, and magnitude, depletion among physicists on the of the layer, which would cause increased during a 1942 seminar at Berkeley some three radiation to fry all humans who dared to years before the first test of an atomic weapon. venture outside, became the extinction mechanism Chaired by Robert Oppenheimer, it was attended of concern. Again, one popular book, The Fate of by , , Emil Konopinski, the by Jonathan Schell,8 which described the and other theoretical physicists.4 They considered nuclear destruction of the leaving the the possibility that detonation of an atomic bomb earth “a republic of insects and grass,” promoted could ignite a self-sustaining nitrogen fusion this . Schell did at times try to cover all bases, reaction that might propagate through earth’s however: “To say that is a , thereby extinguishing all air-breathing certainty would, of course, be a misrepresentation— life on earth. Konopinski, Cloyd Margin, and Teller just as it would be a misrepresentation to say that eventually published the calculations that led to extinction can be ruled out.”9 the conclusion that the nitrogen-nitrogen reaction Finally, the current mechanism of concern for was virtually impossible from atomic bomb extinction is , the phenomenon explosions—calculations that had previously been by which dust and created primarily by the used to justify going forward with , the first 5 burning of cities would rise to the and atomic bomb test. Of course, the Trinity test was attenuate sunlight such that surface temperatures conducted, as well as over 2000 (by all nations) would decline dramatically, agriculture would subsequent atomic and thermonuclear tests, and fail, and humans and other would perish we are fortunately still here breathing air. from . The public first learned of the After the bomb was used, extinction fear focused possibility of nuclear winter in a Parade article by on invisible and deadly fallout, unanticipated as a ,10 published a month or so before its significant consequence of the bombings of Japan, scientific counterpart by Turco et al.11 While some that would spread by global air currents to poison advocates promote the idea the entire planet. Public dread was reinforced by that nuclear winter is an extinction threat, and the the depressing, but influential, 1957 novel On the general public is probably confused to the extent it

2 Schelling, “An Astonishing Sixty Years; and Tannenwald, 6 Shute, . Nuclear Taboo. 7 3 Kramer, On the Beach. I am indebted to Edward Toton for his substantial 8 contributions to this discussion based on his current research Schell, Fate of the Earth. on global catastrophic risks. 9 Schell, Fate of the Earth. 4 Rhodes, Dark . 10 Sagan, “Nuclear Winter.” 5 Konopinski, Margin, and Teller, Ignition. 11 Turco et al., “Nuclear Winter.” 4 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY is not disinterested, few scientists seem to consider Senator Richard Lugar published The Lugar Survey it an extinction threat. on Proliferation Threats and Responses (hereinafter, the Lugar survey), which addresses the risk of It is understandable that some of these extinction 13 were created by ignorance or uncertainty and nuclear use. Among the questions asked in the treated seriously by worst-case thinking, as seems survey was, “What is the probability (expressed appropriate for threats of extinction. But nuclear as a percentage) of an attack involving a nuclear doom mongering also seems to be at play for explosion occurring somewhere in the world in the some of these episodes. For some reason, portions next ten years?” The distribution of replies from 79 of the public active in nuclear issues, as well as respondents is shown in Figure 2. some scientists, appear to think that arguments What is most striking about Figure 2 is the diver- for nuclear arms reductions or elimination will gence of opinion. Responses span the full spectrum be more persuasive if nuclear war is believed to from 0 to 100%, with the mode occurring at 1–9%, threaten extinction, rather than merely the horrific but with only 18 respondents selecting that bin. cataclysm that it would be in reality.12 From a classical statistics perspective, the true prob- To summarize, nuclear war is a global catastrophic ability lies in only one unknown bin. The fact that risk. Such wars may cause billions of deaths and most experts’ answers missed that value, whichever unfathomable suffering, as well as set bin it lies in, means that most experts must neces- back centuries. Smaller nuclear wars pose regional sarily be wrong. There are a number of possible ex- catastrophic risks and also national risks in that the planations for this. One reason for the wide varia- continued functioning of, for example, the United tion could be the lack of control of biases in the States as a constitutional republic is highly dubious elicitation of the answers. Without bias control, ex- after even a relatively limited nuclear attack. But what perts can interpret and think differently about how nuclear war is not is an existential risk to the human to answer the question, resulting in wide variability. race. There is simply no credible scenario in which Even if biases are controlled, wide dispersion can humans do not survive to repopulate the earth. still occur because of high uncertainty in the current state of knowledge. In any event, the most signifi- cant conclusion to be drawn from Figure 2 is that Risk Assessment there is no consensus on the answer to the question. With this foundation, I now turn to assessments of In other respects as well, the Lugar survey did not 14 the risk of nuclear war, first addressing likelihood follow best practices in elicitation and analysis. and then consequences. While each survey respondent was presumably an expert in some aspect of nuclear policy, arguably no single person is truly an expert on all the Likelihood factors that must be considered when answering Consider the current state of analysis for assessing broadly phrased questions such as that depicted 15 the likelihood of nuclear war. In 2005, the office of in Figure 2. Additionally, the survey provides

13 12 Lugar, Lugar Survey. Martin, “Critique of Nuclear Extinction.” As summarized by 14 Martin, “The idea that global nuclear war could kill most or all Meyer and Booker, Eliciting; see also Ayyub, Elicitation. of the world’s population is critically examined and found to 15 According to the Lugar survey, “Many of these men and have little or no scientific basis.” Martin also critiques possible women have dedicated their professional careers to the study reasons for beliefs or professed beliefs about nuclear extinction, and practice of preventing weapons of mass destruction and including exaggeration to stimulate action. materials from falling into unauthorized hands. Others have Nuclear War as a Global Catastrophic Risk 5

Figure 2. The Lugar Survey, Question 5 no information about the experts’ assumptions, years. As shown in Figure 3, the time of greatest reasoning, and uncertainties. Such information danger—two minutes to midnight—was set in 1953 could, for example, be useful in understanding after US and Soviet hydrogen bomb tests, while the the apparently anomalous peak at 50–59% and the time of least danger, seventeen minutes to midnight, extremes of 0 and 100%. The cumulative impact of was set in 1991 after the START Treaty was signed these and other deficiencies is that the survey falls and unilateral initiatives on both sides removed far short of what could be achieved by using best many nuclear weapons from “hair-trigger” alert.17 practices in expert elicitation. There are multiple problems with taking the clock Another exercise in characterizing the likelihood of seriously as an assessment of the likelihood of nuclear war has been ongoing since 1947, when the nuclear war. In setting the clock, there could be Doomsday Clock first appeared on the cover of the motives beyond accurately characterizing the Bulletin of Atomic Scientists.16 The setting of the nuclear threat, such as to promote certain policies, clock is intended to represent how close the world is especially with respect to arms control treaties, or to nuclear war, metaphorically midnight. The clock simply to draw attention to the Bulletin of the was originally set at seven minutes to midnight and Atomic Scientists. The process by which the clock has been reset periodically every several (1 to 7) is set is obscure, although brief summaries of the reasons for changing the clock’s setting have been provided.18 No attempt has been made to been national security leaders within their countries. As a group, they possess enormous experience in the fields of define the clock’s scale, which is almost certainly non-proliferation, counter-proliferation, diplomacy, military nonlinear. Does ten minutes to midnight indicate affairs, arms inspection, intelligence gathering, and other half the probability of five minutes to midnight? national security fields relevant to the questions asked.” The And finally, the clock is unable to reflect the risks fault of the survey is to confuse the expertise of the group as a whole, if it could be brought to consensus, with the sum of indi- vidual expertise within the group. 17 Bulletin of the Atomic Scientists, Timeline. 16 Bulletin of the Atomic Scientists, Doomsday Clock Overview. 18 Bulletin of the Atomic Scientists, Timeline. 6 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

The clock indicates then-current perspectives of the Bulletin of the Atomic Scientists on the dangers of nuclear war. Since 2007, dangers associated with change and developments in the life sciences have been added. Figure 3. The Doomsday Clock, 1947–2004 associated with short-duration, high-risk episodes, Table 1. Most are subjective judgments (such as such as the of 1962 and the those of Kennedy,20 Bundy,21 Allison,22 Perry,23 coup attempt against Gorbachev in August 1991.19 Albright,24 and Garwin25) without a formal Ironically, the former occurred during a period of underlying analysis, while others are based on a declining risk, according to Figure 3, and the latter quantitative analysis (such as those of Hellman,26 occurred during the period of least risk. Bunn,27 and Mueller28). Notwithstanding these points, the Doomsday Clock Arguably, the most compelling assessments are does seem to have captured the broad trends in the those of crisis managers who experienced a nuclear nuclear threat as it derives from the international close-call firsthand: President Kennedy and his political climate. Gaining a better understanding national security advisor, McGeorge Bundy. Not of the processes by which the clock has been set long after the Cuban missile crisis, Kennedy told could prove useful in developing more scientific Ted Sorenson, special counsel to the president, that approaches. Unfortunately, the clock’s future utility as an indicator of the risk of nuclear war has been 20 Sorensen, Kennedy. diminished since 2007 by the inclusion of climate 21 Bundy, Danger and Survival. change and harmful developments in the life 22 Allison, Nuclear . sciences as additional harbingers of doomsday. 23 Kristof, “An American Hiroshima.” Several individuals have also estimated the 24 Hegland and Webb, “The Threat.” likelihood of interstate nuclear war or nuclear 25 Garwin, Testimony. terrorism. Selected estimates are summarized in 26 Hellman, “Risk Analysis.” 27 Bunn, “Guardians at the Gates of Hell.” 19 Pry, War Scare. 28 Mueller, “Atomic Terrorist.” Nuclear War as a Global Catastrophic Risk 7

Table 1. Individual Estimates of the Probability of Nuclear War

Probability that the Cuban missile crisis could have escalated to (nuclear) war

Between 1 in 3 and even John F. Kennedy 1962

Up to 1 in 100 McGeorge Bundy 1988

Probability of a future Cuban missile-type crisis that results in nuclear use

2 in 1000 to 1 in 100 per year Martin Hellman 2008

Probability that terrorists will detonate a nuclear bomb

50% probability within the next decade Graham Allison 2004

50-50 odds within the next decade William Perry 2004

1% probability over 10 years David Albright 2005

29% probability within the next decade Matthew Bunn 2007

Less than 1 in 1,000,000 per attempt John Mueller 2008

20% per year against a US or European city Richard Garwin 2007 during the crisis he believed that the chances that Of course, beyond the question of what the the Soviets would go to war were between 1 in 3 actual risk was at the time of the Cuban crisis is and even, while Bundy, reflecting 26 years after the the problem of the relevance of that information crisis, came to the dramatically lower estimate of to the assessment of future risks. More recently, up to 1 in 100. Of course, the crisis occurred over Martin Hellman assessed the risk of a future a half-century ago, and even with the additional “Cuban-missile-type” crisis that results in nuclear information now available, it is hard to estimate its use as between 2 in 1000 and 1 in 100 per year. Note risks retrospectively. For example, depending on that this is only one of two estimates in Table 1 that one’s interpretation of the probabilities associated provide a range of values, a useful approach to with the incident in which a nuclear-armed Soviet addressing uncertainty. Hellman also points to a submarine was forced to surface, and the risks dearth of analyses of the risk of deterrence failure one should attach to other “close-call” incidents and proposes that “several prestigious scientific during the Cuban crisis,29 one could argue for and engineering bodies undertake serious studies either Kennedy’s estimate or Bundy’s. Moreover, to estimate its failure rate.” neither Kennedy nor Bundy knew at the time they Not surprisingly, a number of estimates in the made their estimates that the Soviet submarine had first decade of this century have focused on the come close to launching a nuclear , but they probability of nuclear use by terrorist organizations. could have imagined this and other scenarios as Of the subjective estimations, Richard Garwin’s part of their risk estimates, so it is unclear whether estimate of 20% per year against a US or European either of them would have raised or lowered their city is the highest. Assuming that this probability estimates if they had known at the time of their remains constant over the period, it equates to a estimates everything we know now. probability of approximately 90% within a decade. In the middle of the range of subjective estimates 29 Sagan, Limits of Safety. 8 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY are Graham Allison and William Perry, who out of some nuclear usages. In particular, limited independently judge this probability to be 50% nuclear use might reinforce the nuclear taboo, within a decade. At the low end is David Albright, which is seen as increasingly fragile.30 Of course, as who estimates it to be less than 1% over 10 years. Hahn et al.31 observe: These subjective assessments span almost the The greatest challenge to this norm will complete range of possibility from near 0 to 90%. occur when nuclear weapons are used. Two estimates in Table 1 are based There is a presumption that once violated, on quantitative analysis. Matthew Bunn estimates the norm against use of nuclear weapons 29% within the next decade, and John Mueller cannot endure. But, this presumption is not estimates less than 1 in 1 million per attempt. This based on a body of research; it is possible large difference in estimates is not an encouraging that the response to first use could act to indicator that quantitative analysis will facilitate reaffirm the relevance of the norm and that convergence on a consensus estimate, but at least it a single violation would not necessarily provides valuable information regarding the basis irreversibly undermine the norm’s exis- for each estimate. tence. In fact, norm theory suggests that In summary, the principal insights I take from the the response to the norm violation can be estimates in Table 1 are the same as for the Lugar pivotal in determining the ultimate impact survey: (1) they differ widely, and (2) they are all of of the initial violation. questionable validity because they do differ widely An extension of this thinking holds that norms, in and because they are fundamentally either intuitive general, cannot endure indefinitely without periodic or based on simple, perhaps simplistic, analysis. violations that provide tangible reminders of their Also, subjective judgments appear to gravitate value. In any event, this area is highly speculative, to either 1 or 50% as an estimate, which suggests and no one seriously advocates limited nuclear use that the resolution of human intuition is relatively as a mechanism to reinforce the nuclear taboo. coarse on this question. Our knowledge base on nuclear effects is extensive in some areas but meager in others.32 It is not an Consequences exaggeration to say that, as a whole, it is woefully inadequate to support a comprehensive conse- Nuclear risk assessment must consider the entire quence assessment. There are several reasons for spectrum of potential consequences of all levels this state of affairs. First, while the United States of nuclear war, ranging from a single detonation has conducted over 1000 nuclear tests and spent in a remote area to a large-scale nuclear exchange. billions of dollars on nuclear effects research, the These consequences must include all types of great majority of this effort focused on fulfilling harm, including fatalities and injuries to humans, Cold War military requirements. In support of damages to infrastructures and the environment, nuclear mission planning, the United States sought and harm to militaries, economies, and other social high-confidence estimates of the effects of nuclear structures. Assessments must consider not only the short-term harms but also harms that extend 30 Tannenwald, “Vanishing Nuclear Taboo?” through time to future generations, likely centuries 31 Hahn et al., Responding to North Korean Nuclear First Use, into the future. forthcoming. 32 We should also acknowledge, if only for the sake of A more detailed exposition of the remainder of this section completeness, that something positive might come may be found in Frankel, Scouras, and Ullrich, Uncertain Consequences. Nuclear War as a Global Catastrophic Risk 9 weapons of various designs with different outputs the Department of Homeland Security has funded on targets of varying characteristics primarily in the National Infrastructure Simulation and the . Post-attack planning for damage Analysis Center (https://www.sandia.gov/nisac- assessment and the possible need for subsequent ssl/), an effort by Sandia National Laboratories, attacks also demanded confidence in determining Los Alamos National Laboratory, and Pacific target damage. These imperatives led to a focus Northwest National Laboratory to model the inter- on the nuclear damage mechanisms of air blast, dependencies among these infrastructures, albeit cratering, ground shock, and similar phenomena. with limited success. Nonphysical societal effects As a result, our knowledge base is relatively good (e.g., social, psychological, political, and economic on these nuclear effects. effects) are even more difficult to assess and have Second, somewhat less attention was paid to those never been adequately investigated. phenomena that were inherently hard to predict or Arguably, the two phenomena most in need of whose effects were delayed. In the former category further research are nuclear winter and EMP. is fire initiated by the thermal radiation of nuclear Nuclear winter has the potential to pose even explosions. The US Defense Nuclear Agency, now greater harm to life on earth than all the more the Defense Threat Reduction Agency, tried hard to immediate damages due to blast and prompt model this phenomenon, but only very recently has radiation. A small research community continues this effort showed signs of potential payoff. In the to model nuclear winter in various nuclear war latter category is fallout. While fallout modeling scenarios with ever-more sophisticated models. was a research focus, and we now have good models But controversy over the many uncertainties of fallout production and propagation, the vagaries associated with the inputs to these models and the of weather, the uncertainties related to population underlying physics, as well as possible antinuclear evacuation and shielding, and other variables are biases of some of the researchers, has impeded impediments to confident prediction of the effects acceptance of nuclear winter predictions. As a of fallout. result, the Department of Defense simply does not Third, some phenomena were discovered late, consider nuclear winter in its policy formulation or and by surprise, in the nuclear test program. For military planning. In fact, it argues that by making example, an unexpectedly large EMP was observed nuclear war even more horrific, nuclear winter is in the Starfish Prime atmospheric nuclear test in a positive contribution to deterrence. Similarly, the 1962. Further high-altitude testing was prohibited consequences of EMP may be catastrophic, but we by the 1963 Treaty Banning Nuclear Weapons simply do not know whether a nuclear attack will Tests in the Atmosphere, in Outer Space, and bring down the electric grid or otherwise cause great damage to the electronic systems that power Under Water, which relegated future research 33 to the domain of modeling. Starfish Prime also our economy, military, and society. resulted in the unanticipated gradual destruction As a result of this limited state of knowledge of of all commercial satellites in low earth orbit due the consequences of nuclear war, a comprehensive to pumping the Van Allen radiation belts with consequences assessment is simply not possible. electrons. The best we can do is estimate lower bounds on consequences and recognize that the true conse- Fourth, the physical consequences to the infra- structures that sustain societies—power, water, quences of nuclear war may be significantly higher. finance, transportation, etc.—has never been a focus of nuclear weapons effects research. However, 33 Frankel, Scouras, and DeSimone, Assessing the Risk. 10 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

Risk Management It is not entirely clear why the development and possession of nuclear weapons by Japan or South Notwithstanding our limited understanding of Korea, for example, would not similarly contribute both the likelihood and consequences of nuclear to international security, especially because war, there is no shortage of ideas about what to further proliferation in northeast is unlikely do about nuclear risk. The three pillars of US to be provoked. More generally, Kenneth Waltz policy are (1) nonproliferation to reduce the has argued that the more states that have nuclear threat from an ever-increasing number of nuclear weapons, the safer the world will be from nuclear states, (2) counterterrorism to prevent nonstate war.34 His argument is consistent with the historical organizations from acquiring nuclear materials experience that demonstrates that and weapons, and (3) deterrence to prevent attack states have shown great forbearance in engaging in from hostile nuclear states. I will briefly address direct combat with each other. the first two of these, and then discuss in greater depth the role of the nuclear balance and arsenal In any event, proliferation is also dangerous be- size in underwriting deterrence strategy. My main cause new nuclear states pose special risks that point is that there are large uncertainties and a lack established nuclear states do not. One such risk of consensus regarding the benefits of alternative arises from the fact that they have little or no ex- policies proposed to manage nuclear risk. I do not perience with nuclear diplomacy and crisis man- address a multitude of other ideas, such as reducing agement, which could lead to reckless posturing dependency on , increasing (or or behavior. We may have witnessed this dynamic decreasing) missile defenses, moving toward a in the 2018 war of words between US President nuclear-free world, and formulating policies that and North Korean Supreme Leader 35 reflect the complex relationships among strategic Kim Jong Un. nuclear weapons, tactical nuclear weapons, and Another source of proliferation risk arises from conventional, cyber, and space capabilities. These the reactions—especially threats of preventive approaches are also fraught with uncertainties and war—of established nuclear states to nascent lack consensus. nuclear states. Preventive war was considered— and rejected—by the United States to counter Nonproliferation a prospective nuclear Soviet Union and by the Soviet Union to counter a nascent nuclear China. It might seem obvious that the fewer the number More recently, to counter the prospective threat of nuclear states, the safer we are, and indeed that from “rogue” states, President George W. Bush appears to be the consensus view in the national emphasized the need for preemptive attack options security community. The main argument is that in our deterrence strategy. with fewer nuclear states, there are fewer pathways to nuclear war. This may be true, but it is not the Counterterrorism whole story. The United States benefits from both the British and French nuclear arsenals in deterring After the attacks of September 11, 2001, fear from nuclear and large conventional attacks that a terrorist organization would succeed in in Europe. This is not primarily because of our stealing, building, or buying a nuclear weapon allies’ arsenals themselves, but because they provide dominated nuclear concerns. The thought was that independent decision authorities that Russia must consider when contemplating an attack. 34 Sagan and Waltz, Spread of Nuclear Weapons. 35 Ice et al., Game Theory and Nuclear Stability. Nuclear War as a Global Catastrophic Risk 11

Data through 2010 are from Norris and Kristensen, and data after 2010 are from Kristensen and Korda. Figure 4. US and Soviet/Russian Nuclear Arsenals over Time such organizations were immune to the logic of of nuclear parity, and (2) how many weapons are deterrence, because they did not present targets of enough to underwrite deterrence. value in the way that established states do. Hence, counterterrorism strategy focused on preventing Nuclear Parity substate actors from acquiring both weapons and nuclear materials. These efforts have been largely The imperative to achieve nuclear superiority— successful—so far—although more can and should or, at a minimum, nuclear parity—drove the Cold be done. Terrorist organizations are unlikely to have War to dizzying heights, as illustrated given up their nuclear ambitions. More recently, we in Figure 4 (data through 2010 are from Norris 36 have begun to understand that deterrence still has and Kristensen, and data after 2010 are from 37 a role to play against terrorism. But the focus of Kristensen and Korda ). Yet, the United States deterrent threats must be the countries that harbor has also voluntarily tolerated a significant imbal- terrorist organizations, either willfully or through ance in nuclear weapons during the last decade of neglect or incompetence. the Cold War and the first post–Cold War decade, and China has embraced a minimum deterrence posture. As we look ahead, we must consider the Deterrence potential for both further negotiated arms reduc- Deterrence of a nuclear first strike depends on tions and the opposite—abandonment of strategic the fear of a retaliatory strike, which, in turn, arms control—as well as continuing growth in the depends on the nuclear capabilities of the victim of Chinese arsenal and vertical and horizontal nuclear the first strike. Here I summarize two studies that proliferation in other states. Facing this highly illustrate the complexity of assessing the relationship 36 between nuclear capabilities and deterrence. These Norris and Kristensen, “Global Nuclear Weapons Inventories, 1945–2010.” studies address (1) the importance, or irrelevance, 37 Kristensen and Korda, FAS Nuclear Notebooks. 12 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

Figure 5. Uncertainty in the Probability of Winning a Nuclear Crisis entropic future, how should nearly three-quarters implementing the 2018 Nuclear Posture Review, of a century of nuclear experience inform US policy strategic arms control after the New START Treaty, with respect to the nuclear balance with Russia and the future (if any) of a possible successor to the other adversarial nuclear states? Intermediate-Range Nuclear Forces Treaty, and the Because all targeted states would suffer enormously fate of the Comprehensive Test Ban Treaty. They in a nuclear war regardless of the nuclear balance, will also impact US crisis management strategy nuclear crisis management is the default mecha- vis-à-vis , China, and Russia and nism through which the nuclear balance affects nonproliferation policy vis-à-vis . states’ behaviors, and nuclear crisis outcome is the Recent research has incorporated quantitative primary measure of the value of nuclear superiority. analysis into traditionally qualitative investigation. Scholars and strategists debate the importance of However, there are concerns about the appropri- relative nuclear capabilities as well as myriad other ateness of these studies’ statistical methods. One factors, including political stakes, resolve, risk important result of a recent analysis is displayed in tolerance, the conventional military balance, and Figure 5.38 Based on historical data on nuclear crises domestic politics. Multiple factors are often at play compiled by Matthew Kroenig,39 the probabilities in any particular crisis, and there are important of winning a nuclear crisis are plotted for both the relationships among them. The key policy-relevant side with the superior and the side with the inferior question for the United States is, Are nuclear-supe- nuclear arsenal. Both probabilities are highly rior states more likely to prevail in nuclear crises? uncertain, reflections of the small data set and the Perspectives on this question underlie national importance of variables other than the nuclear security policies regarding, inter alia, arms control, balance. Notwithstanding these uncertainties, the triad recapitalization, nonstrategic weapon de- probability of winning is significantly lower with ployments, , nuclear crisis management, and deterrence. Over the next decade, 38 Rooker and Scouras, Nuclear Crisis Outcomes. these perspectives will be reflected in decisions on 39 Kroenig, “Nuclear Superiority.” Nuclear War as a Global Catastrophic Risk 13

Figure 6. Measures of Effectiveness for Nuclear Weapons an inferior arsenal. Nevertheless, the side with How Much Is Enough? the inferior nuclear arsenal does occasionally win Even after we answer the parity question, we still nuclear crises. These results suggest that (1) if a have the related question about how many nuclear nuclear state anticipates nuclear crises in its future weapons we need. Figure 6 shows US nuclear and wishes to win, it should strive to avoid nuclear warheads under the New START Treaty.40 Five states inferiority; and (2) even the side with the superior of these forces are arrayed along the -axis. The arsenal should not confidently expect to win a total number of warheads is equivalent to arsenal nuclear crisis. size. It includes both deployed and nondeployed To summarize, the importance of the nuclear warheads. Available warheads, which exclude balance vis-à-vis our principal adversary has been nondeployed warheads, are those that realistically the subject of intense but unresolved debate since could be used in a nuclear war. But not all available the Soviet Union acquired nuclear weapons some warheads are on alert, ready to be launched within seven decades ago. Though nuclear superiority has minutes of a presidential order, or are based in a not always swayed crisis resolution, it has mattered survivable posture available to be launched at any in at least some crises. Thus, we cannot ignore the time. On day-to-day alert, fewer than half of the possibility that it will matter in some future crises— available warheads could be launched rapidly or perhaps even the next crisis. Given profound are survivable. Then, we must consider whether the uncertainties about the implications of asymmetries United States launches intercontinental ballistic in nuclear arsenals, it would seem the most prudent missiles on tactical warning (LOW) or rides out approach is to hedge against the possibility of dire an attack (ROA). Riding out the attack will further consequences of nuclear inferiority. Nevertheless, decrease the warhead count. Finally, we must the contrary view that the United States would factor in the system reliabilities and probabilities be safe even after unilateral deep cuts in nuclear arsenals cannot be dismissed out of hand. 40 See chap. 2 of Cimbala and Scouras, A New Nuclear Century, for a more detailed discussion of this graphical representation. 14 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY

Figure 7. Wartime Fatalities as a Percentage of World Population, as Appears in the 2018 Nuclear Posture Review Report of penetrating Russian defenses. At the end, we So, what level of assured retaliation is sufficient? are left with the number of warheads that we—and This has been subject to debate throughout the Russia—can reasonably anticipate would detonate nuclear age. During most of the Cold War, we in a US retaliatory strike on Russian targets. It is focused on being able to achieve high damage levels this quantity—arriving warheads—not arsenal size to military, economic, and leadership targets in the or any of the other intermediate quantities, that Soviet Union. And as our arsenals grew, so did our underwrites deterrence. target lists. The prevailing view was that deterrence In Figure 6, we see four scenarios with different required us to be able to utterly destroy the Soviet numbers of arriving weapons. The lowest level is Union as a functioning entity in a retaliatory strike defined as assured retaliation. I argue that our focus under the worst plausible circumstance. As a point should be on this number as the single best measure of reference, to Secretary of Defense Robert S. of our nuclear forces’ contribution to deterrence. McNamara this meant being able to destroy one-third of the Soviet population and one-half of Although it might not be the most likely of the four 41 scenarios, it is still probable enough, relative to its industry. the others, that we must plan for it. Furthermore, Today, other views are gaining traction. At this while we may be able to control whether or not we point, there appear to be two main intellectual ride out an attack or launch on warning, there is camps among deterrence analysts, one cautioning great uncertainty in what we will actually do. Thus, against going to lower levels and the other we should not count on launching on warning. advocating at least some additional nuclear arms And finally, whether we are on generated alert as reductions. There are important distinctions within opposed to day-to-day alert is actually a decision the group that advocates for further reductions. that our attacker will make, because the timing of any attack would be up to them. 41 McNamara, Remarks. Nuclear War as a Global Catastrophic Risk 15

Figure 8. Recalculated Annual Wartime Fatalities as a Percentage of World Population

Some call for modest bilateral reductions under a singular analysis of wartime fatalities from the year negotiated treaty, although that seems improbable 1600 to the present. While the original graph of the at least for the next several years. Others call for results of this analysis was circulated in the defense a US minimum deterrence posture, independent community in the mid-1990s, it has evolved over of the size of the Russian arsenal. Proponents of the decades, with the most recent variant (shown minimum deterrence argue that far fewer weapons in Figure 7) appearing in the 2018 Nuclear Posture (arsenals numbering in the hundreds) are sufficient Review report. It indicates that wartime fatalities to deter Russia. They point to China, and to a lesser have been lower in the nuclear era than during any extent the UK and France, all of which have adopted previous time since 1600, implicitly crediting the variants of minimum deterrence postures. advent of nuclear weapons for these saved lives. Ice, Scouras, and Toton42 analyzed this graph and Residual Risk and Risk Acceptance found that it is fatally flawed. In particular, it is irreproducible from information provided by the It is clear that we cannot reduce nuclear risk to Department of Defense Historical Office, the cited zero unless we eliminate all nuclear weapons from source of data; it uses dubious analytical methods the earth, and perhaps not even then. And while (among them, concatenation of incompatible President Obama was a strong advocate for “global databases and erroneous normalization by world zero” as a long-term objective, no other nuclear population); and it presents results in a profoundly state seems to have seriously embraced this vision. misleading manner, primarily due to varying But there is also a possible serious downside to histogram bin widths. reducing nuclear risk to zero. Citing the absence of A more rigorous analysis results in the graph great-power wars since 1945, some proponents of in Figure 8.43 All the cited flaws of the preceding nuclear weapons have emphasized their importance in saving lives by reducing the frequency and intensity of conventional wars between great powers. 42 Ice, Scouras, and Toton, Wartime Fatalities.. To support their viewpoint, they often point to a 43 Ice, Scouras, and Toton, Wartime Fatalities. 16 THE JOHNS HOPKINS UNIVERSITY APPLIED PHYSICS LABORATORY histogram have been rectified. In particular, Our understanding of the risk of nuclear war wartime fatalities are shown on an annual basis, is highly uncertain, both for likelihood and which enables more insight into the aperi- consequences. But steps can be taken to improve odic of wartime fatalities and entails less this situation. Regarding likelihood assessments, bias. This graph indicates that the incidence of the first important step is to develop a more refined annual wartime fatalities after World War II (as a sense of humility about whatever intuition is percentage of world population) is comparable to informing our judgments. We can and should also that of many earlier times. Also, periods of dimin- undertake more disciplined analytic studies. These ished fatalities typically follow major wars; for this should be multidisciplinary because no single reason alone, we cannot conclude with certainty analytic approach has proven to be satisfactory. We that nuclear weapons are the source of the current can learn something from historical case studies, relatively quiescent period. Finally, we observe a expert elicitation, probabilistic risk assessment, clear trend in the intensity of major wars. Projecting complex systems theory, and other disciplines. this trend to the future reminds us what we already Regarding consequence assessments, the Defense know—that nuclear war will be unprecedented in Threat Reduction Agency needs explicit direction its human toll, potentially exceeding the fatalities to focus on less understood nuclear effects, of all previous wars combined. There is simply particularly EMP and nuclear winter. Even absent no basis in this analysis to conclude that nuclear further nuclear testing, there are no fundamental weapons will continue to deter either nuclear or barriers to obtaining a better understanding of large-scale conventional war. these important phenomena. Finally, it is important to understand that historical It is also apparent that the optimal strategy for statistical analysis—done correctly—can at most reducing nuclear risk is also uncertain. This show a correlation between the advent of nuclear suggests a cautionary and balanced approach. weapons and a change in wartime fatalities. Extremes, such as global zero or replacing nuclear Proving a causal relationship would require a deterrence with widely deployed missile defenses, complex multidisciplinary analysis. Understanding are untested gambles and either politically or the potential for nuclear weapons to prevent great technologically prohibitive. Some combination powers from waging conventional war is a worthy of measured and slowly implemented reductions, pursuit that deserves a thorough and rigorous while maintaining parity with our largest adversary, analysis. Basing vital national security decisions seems prudent. on irreproducible, misleading, and logically flawed Because the stakes are so high, nuclear deterrence reasoning is a dangerous practice. (like liberty) requires eternal vigilance. The good news is that we can afford whatever we decide Final Thoughts and we need to underwrite nuclear deterrence. As Recommendations remarked by Secretary of Defense James N. Mattis, “America can afford survival.”44 But spending Nuclear war is a global catastrophic risk that will money is the easy part. The challenge is to decide be with us for the foreseeable future. Unlike most wisely what we need to spend it on. other global catastrophic risks, there is an interplay between consequences and likelihood that forces us to question just how much we should try to reduce either component of risk. 44 James N. Mattis, Remarks. Nuclear War as a Global Catastrophic Risk 17

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Nuclear War as a Global Catastrophic Risk 21

About the Author

James Scouras is a senior scholar at APL and the former chief scientist of the Defense Threat Reduction Agency’s Advanced Systems and Concepts Office. Previously, he was program director for risk analysis at the Homeland Security Institute, held research positions at the Institute for Defense Analyses and the RAND Corporation, and lectured on nuclear policy in the University of Maryland’s General Honors Program. Among his publications is the book A New Nuclear Century: Strategic Stability and Arms Control (Praeger, 2002), coauthored with Stephen Cimbala. Publication of his edited volume, On the Risk of Nuclear War, is anticipated in 2020. Dr. Scouras earned his PhD in physics from the University of Maryland.

NUCLEAR WAR AS A GLOBAL CATASTROPHIC RISK

National Security Report

James Scouras