NUCLEAR WAR AS A GLOBAL CATASTROPHIC RISK National Security Report James Scouras NUCLEAR WAR AS A GLOBAL CATASTROPHIC RISK James Scouras Copyright © 2020 The Johns Hopkins University Applied Physics 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: • Martin Hellman’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 Doomsday Clock, 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 Weapons ................................................................................... 13 Figure 7. Wartime Fatalities as a Percentage of World Population, as Appears in the 2018 Nuclear Posture Review Report ....................................................................................................................... 14 Figure 8. Recalculated Annual Wartime Fatalities as a Percentage of World Population .......................... 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 winter may result in more fatalities across the globe than the better-understood effects of blast, prompt radiation, and fallout. Electromagnetic pulse 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 risks 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 Cold War 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 nuclear holocaust. 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 weapon 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 Hiroshima and Nagasaki, 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