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Risk Analysis Methods for Nuclear War and Nuclear Terrorism (2023)

Chapter: 3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism

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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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3

The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism

This chapter reviews the key research in the assessment of the risks of nuclear war and nuclear terrorism. It provides an overview of major developments and insights, with a primary focus on U.S. policy and risk assessment.

THE HISTORY AND LITERATURE OF RISK ASSESSMENT FOR NUCLEAR WAR

Over the decades, much has been written about the risks of nuclear war or how particular situations, policies, or weapons might affect it. The nature of the concerns and the methods used to evaluate them have evolved over the decades.

1940s and 1950s

In the years immediately following World War II, there was widespread concern that future wars could lead to unprecedented devastation. The U.S. military was still determining how best to use nuclear weapons and developing internal capabilities to make those assessments. The United States quickly moved from a position of nuclear “unipolarity” (holding a monopoly on nuclear weapons and delivery systems) to a bipolar position as the Soviet Union developed nuclear weapons and the means to deliver them.

Early on, some analysts envisioned that nuclear weapons would create such fear that they might prevent future wars. While the concept of deterrence has long

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

been relevant to conventional conflict, the presence of nuclear weapons changed the deterrence landscape (Brodie 1946).

The RAND Corporation (established in 1948) led the development of much of the early U.S. thinking about nuclear strategy and ways to assess different elements of nuclear risks, including a proposal to effectively study the risk of nuclear war to help guide U.S. weapons choices in the context of various war types. The analysis was guided by identification of different scenarios and methods (Ansoff et al. 1951; Wohlstetter 1952; Wohlstetter and Rowen 1952).

RAND’s analysis of nuclear weapons capabilities and vulnerabilities to Soviet surprise attack began early in the Cold War (Freedman 2003). By 1956, the analysts had assessed the vulnerability of U.S. facilities to a Soviet intercontinental ballistic missile attack. This analysis was used in introducing the concepts of first and second strikes into strategic theory (Freedman 2003; RAND 1956). A first strike would begin a nuclear war with the intent of crippling the enemy’s nuclear capabilities and hence its means of retaliation. A second strike would be the retaliation after absorbing an enemy first strike.

Detailed methods were developed to assess the vulnerability of particular weapon deployments to various types of attack and to assess the effectiveness of potential U.S. attacks on Soviet targets. These technical strategic exchange calculations came to underpin much U.S. thinking about nuclear war. While Soviet analysts also performed calculations about the vulnerability of forces and the effectiveness of potential strikes, overall Soviet assessments tended to be more focused on broader geopolitical issues, what the Soviets referred to as the global “correlation of forces” (Sokolovskii et al. 1963).

After a great deal of work on the survivability of U.S. forces, Schelling (1958) raised the concern that the vulnerability of Soviet forces to U.S. attacks could, paradoxically, undermine U.S. security as well. If both sides thought they would be better off if they struck first and destroyed a large portion of the other side’s nuclear forces, and if both sides feared that the other side was thinking the same, Schelling hypothesized that this would increase the risk that one country would decide to attack in a crisis. Schelling’s paper established the concept that came to be known as first-strike stability: if both sides had survivable forces, neither side would have an incentive to strike first, and the nuclear balance would be more stable. While U.S. arms control advocates adopted this idea, arguing that both sides’ security would benefit if both avoided seriously threatening the other’s nuclear forces, in reality, the militaries on both sides continued to pursue the ability to attack each other’s nuclear forces and continue to do so today.

In this era, game theory was used to think through circumstances in which one side or the other might have an incentive to carry out a nuclear strike or agree to and comply with a particular agreement (Dresher 1951; Haywood 1954; Schelling 1980).

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

The 1960s

Two events in the early 1960s focused attention on the real possibility of nuclear war: the Berlin Crisis of 1961 (DOS 1966) and the Cuban missile crisis in 1962 (Allison and Zelikow 1999). These events transformed concepts of nuclear war into very realistic possibilities to the public and affected the U.S. government’s thinking about nuclear threats. During this period, the Kennedy administration introduced the concept of a limited response that would reduce the quantity of weapons launched in response to an initial attack (Ellsberg 2017).

During the 1960s, exchange calculations of the sort initiated in the 1950s became more sophisticated and addressed new issues, producing estimates of the probability of destroying hardened targets (such as missile silos) with weapons of varying accuracy, and the probability of penetrating missile defenses. (Hardened sites began to be tested and deployed by the late 1960s.)

The late 1950s and early 1960s marked the beginning of the U.S. “triad” of nuclear delivery vehicles with different operational advantages:

  • Intercontinental ballistic missiles had accuracy and prompt responsiveness to attack Soviet hardened targets (e.g., weapon silos).
  • Submarine-launched ballistic missiles were considered survivable because of the difficulty in identifying their location while submerged on nuclear deterrent patrol and thus able to retaliate.
  • Land-based bombers could be dispersed quickly to different bases and recalled if the crisis deescalated; they could be launched on warning and return to base under “fail safe” procedures if the warning turned out to be a false alarm.

The United States also deployed thousands of shorter-range nuclear weapons on land and on Navy ships (Woolf 2008).

The Soviet Union adopted a similar approach, which added credibility to the concept of stability arising from mutual assured destruction (Freedman 2003). As nuclear arsenals expanded in the United States and the Soviet Union, stability assessments began to focus not only on crisis stability, but also on arms race stability, including whether the structure of forces was such that either side thought it could get an advantage by expanding its nuclear forces. This thinking led to consideration of how many nuclear weapons the United States should have in its arsenal. Then-Secretary of Defense McNamara announced the idea of assured destruction, whereby the United States needed enough weapons that could survive and retaliate.

Data from nuclear-explosion tests in the 1950s and the 1960s contributed to further analyses of the consequences of nuclear war in the 1960s. Studies of consequences included some of the first analyses of the psychological impact of nuclear

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

weapons (Lifton 1967). Because of the difficulty of assessing the risks of escalating crises or the chance of one side or the other backing down, analysts began to rely more heavily on war games, in which participants would play through various hypothetical crises, trying to understand what circumstances increased or decreased the odds that one side or another would use nuclear weapons.

Game theory continued to be used to understand how countries might respond to nuclear threats. Following the work of Schelling (1960), Kobe (1962) proposed an “autocatalytic” model that provided game theoretical conditions under which one nation would mount a nuclear attack against another, and attendant calculations that estimated the number of consequent deaths.1 Mathematical theorems on fundamental instability of nuclear multipolarity were also advanced (Aumann et al. 1995; Selten and Tietz 1966).

During the 1960s, concerns over the possibility of unauthorized or accidental use of nuclear weapons began to emerge. Assessments of the danger of unauthorized use relied initially on expert judgment and, later, on systems engineering analysis of the difficulty of overcoming the measures put in place to block such use.

By the late 1960s, a series of accidents involving nuclear weapons (particularly, accidents in which thermonuclear weapons were dropped from aircraft or aircraft crashed carrying such weapons) led to a decision to end the U.S. practice of keeping a small number of bombers armed with nuclear weapons in the air at all times. At the same time, there were substantial improvements in the safety design of U.S. nuclear weapons, including such innovations as primary fission components resistant to fire; “insensitive high explosives” that were much more difficult to detonate accidentally; improved arming and fuzing mechanisms that provided high confidence no detonation signal would be sent accidentally (including systems that blocked arming of the weapon until it had been through the expected flight sequence); and, perhaps most important, “one-point safety,” a requirement that the probability of achieving a nuclear yield greater than the equivalent of 4 pounds of TNT in the event of a one-point initiation of the main charge high explosive must not exceed one in a million (DOE 2015). A variety of systems engineering methods based on probabilistic risk assessment were used to assess these safety systems, as similar methods were used in other engineering fields. Few assessments, however, explored in detail how such accidents might lead to nuclear war if they were to occur in a moment of intense crisis (Sagan 1993).

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1 The model required that the number of nuclear powers be greater than or equal to three and that the attacking nation can do so in such a way that the blame for the attack could be shifted to a different nuclear power. Technically, this methodology falls within the scope of this study’s charge, but the committee believes the approach is largely irrelevant because of its strong assumptions, its assumption that the attacker could lay the blame at someone else’s door (which is challenging given intelligence capabilities), and its lack of a probability statement about nuclear war. (Instead, it identifies a set of nonstochastic conditions under which a game theorist would choose to make a sneak attack.)

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

The 1960s also saw increasing concern about the spread of nuclear weapons among countries and the possibility that this spread would lead to more danger of nuclear war—including the possibility that other nuclear-armed states might somehow provoke a U.S.-Soviet nuclear war. This concern was heightened by the Chinese nuclear-explosion test in 1964. Ultimately, this concern led to negotiation of the Nuclear Nonproliferation Treaty, which opened for signature in 1968 and has served as the foundation of the global effort to stem the spread of nuclear weapons ever since. Assessments of this “Nth-country problem” relied primarily on expert judgments; wargaming was also used to explore how additional nuclear-armed countries might affect some types of crises.

The 1970s

The 1970s saw important progress in formalizing probabilistic risk assessment techniques, initially for analyses of the safety of nuclear reactors (NRC 1975). Similar analyses of potential pathways to an undesired outcome, with assessments of each step on the pathway, began to be applied in many other engineered systems, including a reliability model for the command and control of U.S. nuclear forces (Paté‐Cornell and Neu 1985).

The Strategic Arms Limitation Talks I agreements, the Anti-Ballistic Missile Treaty, and the Interim Agreement on offensive forces were all signed in 1972. The Anti-Ballistic Missile Treaty was intended to improve both arms race and crisis stability. The Interim Agreement’s limits—and those of subsequent arms control agreements—offered a degree of predictability and transparency, ultimately reducing hostility between the United States and the Soviet Union. Many assessments explored the pros and cons of different potential arms control provisions, incorporating strategic exchange calculations, intelligence assessments of potential future adversary forces with and without agreed restraints, assessments of verification effectiveness, and the like. Still, critics argued that arms control advocates were seeking agreements for their own sake, more than agreements carefully tailored to increase U.S. security.

In addition to arms control, the United States and the Soviet Union undertook a range of confidence-building measures intended to reduce the risks of armed conflict between them that might escalate to nuclear war.2 At the end of the decade, President Carter issued Presidential Directive 59, calling for a nuclear strategy that included flexible options, including a heavy emphasis on counterforce attacks on

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2 These measures had begun in the 1960s, after the Cuban missile crisis, with the agreement on establishing a hotline for rapid communication between the United States and the Soviet Union. The measures eventually led to the Prevention of Dangerous Military Activities agreement in the 1980s (Campbell 1991).

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

Soviet nuclear forces. The United States continued to build up its strategic nuclear forces, with the MX missile, the Trident submarine-launched missile, air-launched cruise missiles, and the B-1 bomber.

The 1970s also saw controversies over extended deterrence and its credibility. The United States’ withdrawal from Vietnam and its aftermath led a number of allies to question the reliability of U.S. guarantees. In Europe, there were serious debates over whether the Soviet bloc really had a major conventional advantage over North Atlantic Treaty Organization (NATO) forces, necessitating continued reliance on large numbers of tactical nuclear weapons and plans for early use of them should war break out. Moreover, the Soviet Union began replacing older medium-range missiles with the much more capable three-warhead SS-20 missiles, which were seen by some as posing a new threat to Europe for which the United States had no obvious counter. After considerable debate, in 1979 NATO undertook the “dual-track” decision, under which the United States would deploy Pershing II ballistic missiles and ground-launched cruise missiles in response to the SS-20s, while simultaneously seeking to negotiate an agreement limiting such weapons. A variety of military assessment approaches were used to assess the capabilities of conventional forces on each side and of the nuclear missiles being deployed. However, assessments of how much these deployments might affect the risks of nuclear war are not known to this committee.

The 1970s also saw continuing concern over the potential spread of nuclear weapons and the effect it might have on the overall risks of nuclear war, particularly following India’s nuclear test in 1974. The United States began to focus on detecting and stopping nuclear weapons programs in other countries, while both the United States and the Soviet Union worked to convince their allies and nonaligned states to sign the Nuclear Nonproliferation Treaty. China’s nuclear forces grew, though they remained quite small, and relatively little U.S. analysis was focused on assessing possibilities of nuclear war with China.

The 1980s

The 1980s saw some of the most intense hostility of the Cold War in the early part of the decade, a shift toward major arms control progress in the middle of the decade, and the beginning of the end of the Soviet Union and its alliance system toward the end of the decade. Assessments of the risks of nuclear war and how best to address them had a difficult time keeping up with the pace of change.

President Reagan came to power supporting a major buildup of U.S. military capabilities to achieve “peace through strength,” and he accelerated the increase in investment in U.S. nuclear forces begun in the Carter administration. Strategic exchange calculations and expert judgments were the main methods used to assess what weapons were needed and in what quantities.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

The 1980s also saw further elaboration of more limited options in U.S. nuclear war planning. A variety of techniques, including expert judgment, exchange calculations, and wargaming, was used to help inform these plans. Additional attention was paid to improving the survivability of systems for nuclear command and control and for ensuring the continuity of government in the event of nuclear war. New investments were made in a variety of systems for communicating with nuclear forces.

The early 1980s saw an increase in superpower tensions that raised both government and public concerns over the risks of nuclear war. In 1983, the Soviet Union accidentally shot down a civilian airliner (mistaking it for an intelligence aircraft). The same year, Reagan launched the Strategic Defense Initiative, calling on scientists and engineers to develop technology that would render offensive nuclear missiles “impotent and obsolete.” Strategic exchange estimates, analyses of potential countermeasures to defenses, and a technical review of the program by the American Physical Society quickly made clear that determining whether the objective of the Strategic Defense Initiative was achievable was at least a decade or more away. But, the program proceeded, with officials sometimes articulating more limited objectives (Bloembergen et al. 1987).

In 1985, Mikhail Gorbachev (who had recently become the general secretary of the Communist Party of the Soviet Union) met with Reagan at a summit in Geneva. The two leaders agreed that neither side would win from a nuclear war and agreed to resume arms control negotiations.

In 1987, Reagan and Gorbachev signed the Intermediate-Range Nuclear Forces Treaty, eliminating the entire class of ground-based missiles (with ranges from 500 to 5,500 kilometers) from their arsenals, including the Soviet SS-20s and a variety of shorter-range systems and the U.S. Pershing II and ground-launched cruise missiles, and incorporating on-site inspections for the first time. The Strategic Arms Reduction Treaty (START), which first called for real reductions in strategic forces on each side, came a few years later.

By this time, assessments of such accords were more complex than they had previously been. A variety of methods—including strategic exchange calculations and engineering and intelligence estimates about the capabilities of particular weapons and how rapidly more of them could be built—were used to assess the degree to which the agreements contributed to crisis stability, improved predictability and strategic force planning, and enhanced transparency of each side’s strategic posture. These assessments included analyses of a potential breakout from these agreements and how readily the United States would be able to detect large-scale violations and respond to them to protect its interests.

The 1980s also saw the first analyses that indicated that nuclear war could cause a “nuclear winter” that could interfere with global food production. Gorbachev noted, in particular, that these assessments informed his work toward nuclear arms

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

reductions. The consequences of large-scale nuclear war continued to influence popular culture, with books such as Jonathan Schell’s The Fate of the Earth (focusing exclusively on the danger of nuclear war) and movies such as The Day After (which Reagan noted in his journal left him greatly depressed).

By the end of the 1980s, superpower tensions were significantly reduced, and communist governments were ending in Eastern Europe without the Soviet government intervention. The most dramatic change was the fall of the Berlin wall in 1989.

The 1990s

The risks of nuclear war and U.S. policies to address it were transformed by the collapse of the Soviet Union in 1991. As the Soviet Union neared collapse, President George H.W. Bush concluded that a change in U.S. nuclear policy was needed, and he made far-reaching changes: unilaterally pledging to eliminate all battlefield nuclear weapons, eliminating all nuclear weapons from Navy surface ships and aircraft (leaving only submarine-launched ballistic missiles and sea-launched cruise missiles on submarines), pulling tactical nuclear weapons back to U.S. soil (leaving only air-delivered bombs in Europe), taking U.S. nuclear bombers off strip alert, and de-alerting missiles scheduled for elimination under START. Gorbachev soon followed with unilateral initiatives and, once the Soviet Union ceased to exist and Boris Yeltsin took power as president of the Russian Federation, he reconfirmed Gorbachev’s initiatives and added others.

One early U.S. response to the Soviet collapse was the Cooperative Threat Reduction program and related efforts in the U.S. Department of State, in which the United States provided funding to work cooperatively with Russia and the other states of the former Soviet Union (and, eventually, elsewhere) to dismantle and secure the nuclear, biological, and chemical weapons and materials remaining from the Cold War.3 Few, if any, unclassified assessments sought to understand how these initiatives affected the risks of nuclear war; rather, attention was focused on engineering, cost, and political assessments of particular projects and how they could best be accomplished.

In 1992, the Strategic Air Command and the Joint Strategic Target Planning Staff (the staff created to build the U.S. nuclear war plans) at Offutt Air Force Base were disestablished, and the U.S. Strategic Command was created. The United States signed START II with the Russian Federation in 1993, in which they agreed to

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3 In 1994 as part of the Budapest Memorandum, Ukraine gave up its Soviet nuclear weapons. In exchange, Ukrainian geopolitical borders were recognized and the country was to receive protection from the use of military force or economic sanctions by the Russian Federation, the United States, and the United Kingdom (Memorandum on Security Assurances in Connection with Ukraine’s Accession to the Treaty on Non-Proliferation of Nuclear Weapons, Budapest, December 5, 1994).

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

eliminate all multiple-warhead land-based intercontinental ballistic missiles. Strategic exchange assessments indicated this would have been a major step forward for crisis stability, since in any attack on single-warhead intercontinental ballistic missiles, the attacker would be disarmed as rapidly as the victim, offering no advantage to a first nuclear strike. Unfortunately, however, the treaty never was implemented.

President Clinton was the first president to produce a Nuclear Posture Review (completed in 1994) to outline U.S. nuclear strategy. Given the scale of change in the global situation, it was perhaps surprising how much continuity there was in the review: the basic precepts of U.S. deterrent strategy remained largely unchanged. The review concluded that the United States should lead but hedge, meaning that it should pursue additional nuclear arms reductions but maintain the ability to return to higher levels of nuclear arms should circumstances change. Key elements of the U.S. nuclear strategy that remained unchanged included maintaining options for limited nuclear war fighting, focusing on counterforce targeting, preserving the option to use nuclear weapons first in a conflict, maintaining very high states of alert, preserving an option to launch missiles on warning of an attack, and maintaining nuclear weapons in Europe.

President Clinton pursued START III discussions with Russia, as well as a variety of initiatives related to monitoring nuclear weapon dismantlement and fissile material storage without revealing classified information. None of these initiatives fully came to fruition. Assessments of these initiatives focused mostly on the potential for long-term steps toward nuclear disarmament rather than how they might affect the probability or consequences of nuclear war.

In 1996, Clinton signed the Comprehensive Test Ban Treaty, but the U.S. Senate never ratified it despite administration assessments that the treaty would help slow nuclear proliferation, could be effectively verified, and would not prevent the United States from maintaining a safe and effective nuclear arsenal.

During this decade, the Nth-country problem again gained prominence. After the 1991 Gulf War, inspections revealed that Iraq had had a large nuclear weapons program, most of which had gone undetected. This led to reformed approaches to the International Atomic Energy Agency (IAEA) safeguards and to control of dual-use exports through the Nuclear Suppliers Group, an international group of nuclear supplier countries aiming to control proliferation through guidelines on nuclear exports.4 Then, in 1994, a crisis over North Korea’s nuclear program led to the Agreed Framework between the United States and North Korea in which North Korea agreed to freeze its plutonium program and allow international inspections in return for shipments of heavy fuel oil, steps toward diplomatic recognition, and construction of two light-water reactors.

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4 See the Nuclear Suppliers Group website at https://www.nuclearsuppliersgroup.org/en.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

In 1995, the Nuclear Nonproliferation Treaty was extended indefinitely. But in 1998, both Pakistan and India carried out nuclear-explosion tests and formally declared themselves as nuclear-armed states, integrating nuclear weapons into their military forces. Meanwhile, with the collapse of the Soviet Union, nuclear theft and smuggling became a serious issue. The possibility of nuclear war occurring beyond the two superpowers—or of another nuclear state or terrorist group provoking a superpower nuclear conflict—began to appear of more concern.

The 2000s

Concerns about nuclear war risks in the 2000s were dominated by two factors: fears of nuclear attacks (or nuclear help to terrorists) by states the United States characterized as “rogue” states in Nuclear Posture Reviews, following the 9/11 attacks in 2001; and souring U.S.–Russian relations.

The George W. Bush administration, like the Clinton administration before it, undertook an overall review of the U.S. nuclear posture. It concluded that the United States needed a new triad that included its offensive nuclear forces, missile defenses, and a responsive infrastructure that would make it possible to build additional nuclear weapons, if needed (Frankel et al. 2016). The review also concluded that it was no longer necessary to size U.S. nuclear forces to match Russian forces; rather, U.S. forces should be large enough to cover the targets called for in U.S. nuclear strategy, regardless of whether Russian forces were larger or smaller.

Seeing potential threats from countries such as North Korea and Iran, the Bush administration accelerated U.S. missile defense plans and pulled out of the Anti-Ballistic Missile Treaty. In response, Russia decided not to implement START II (Arms Control Association 2001). Both sides, however, agreed to the Moscow Treaty, which used the framework and verification mechanisms of START and further reduced the numbers of nuclear weapons.

Extensive assessments were undertaken to examine how different types of missile defenses might address various future threats from North Korea and Iran. Few publicly available government analyses examined, however, the degree to which these same missile defenses might lead Russia and China to build larger offensive forces than would otherwise be the case, and what risks to U.S. security might result.

The dangers of multiple countries now maintaining nuclear arsenals began to garner attention and analysis. These assessments were based in significant part on concerns that accidents, false alarms, miscalculations, inadvertent escalation, and other unplanned events could lead to nuclear war, no matter what safety and security measures were in place.

The Agreed Framework collapsed during the 2000s, and North Korea carried out its first nuclear-explosion test in 2006. As North Korea continued to develop its nuclear forces, assessments focused both on verifying North Korean disarmament

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

if agreement could be reached and on how to deter a nuclear-armed North Korea. These assessments focused primarily on intelligence assessments of North Korean capabilities and intent, technical assessments of the capabilities of U.S. offensive forces and missile defenses, and the use of expert judgment and wargaming to explore different deterrent strategies.

Also in the 2000s, Iran’s secret nuclear efforts were revealed, provoking crises, sanctions, and on-again, off-again talks that ran throughout the decade. China’s nuclear forces continued to expand during the decade but, despite growing Chinese capabilities, the United States did not acknowledge being in a mutual deterrence relationship with China.

Toward the end of the decade, President Barack Obama took power, with a very different vision of the future of nuclear weapons. In his Prague speech in 2009, he laid out a vision of a world free of nuclear weapons, as well as a series of steps he hoped to take to reduce nuclear dangers. He also noted, however, that nuclear disarmament might not be achieved in his lifetime and that the existence of nuclear weapons can serve as an effective nuclear deterrent.

The 2010s and Early 2020s

The Obama administration’s 2010 Nuclear Posture Review, like previous reviews, assessed the adequacy of U.S. nuclear forces to carry out the deterrent missions assigned to them. This assessment involved strategic exchange calculations, technical assessments of the capability and reliability of particular weapon systems, intelligence assessments of adversary weapon systems, and expert judgments about what kinds of threats would deter what types of adversary actions. The assessment left most U.S. nuclear policies intact but indicated a strengthening of negative security assurance:

The United States will not use or threaten to use nuclear weapons against non-nuclear weapons states that are party to the Nuclear Nonproliferation Treaty and in compliance with their nuclear nonproliferation obligations…. The United States affirms that any state eligible for the assurance that uses [chemical and biological weapons] against the United States or its allies and partners would face the prospect of a devastating conventional military response—and that any individuals responsible for the attack, whether national leaders or military commanders, would be held fully accountable. (OSD 2010)

Subsequently, the Obama administration laid out a 30-year $1.2 trillion plan to modernize all aspects of the U.S. nuclear arsenal, including additional safety and security enhancements. That plan was largely developed on the basis of engineering assessments of how long particular weapons in the existing arsenal would last and what would be needed to continue current U.S. nuclear strategies. The Trump administration generally endorsed the modernization program, while adding a

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

low-yield submarine-launched ballistic missile warhead and plans for a nuclear sea-launched cruise missile. The Biden administration has so far mostly continued these previous plans, though the future of the nuclear sea-launched cruise missile is unclear.

The New START treaty was completed in 2010, reducing each side’s deployed strategic forces to 1,550 warheads and 700 launchers. The treaty was subject to a variety of complex assessments: U.S. assessments confirmed that the treaty would be adequately verifiable, that U.S. forces within the limits would be sufficient to carry out their deterrent missions, and that the predictability and transparency offered by the treaty would help in planning U.S. strategic forces.

In the three-quarters of a century living with nuclear weapons, the United States has adopted a national security strategy that has strategic deterrence at its core (Bradley 2007; OSD 2018). As the committee heard in briefings from the U.S. Strategic Command, the United States views deterrence holistically, taking deterrence to refer to decisive influence on an adversary’s decision-making calculus in order to prevent hostile action against vital interests. This view incorporates a recognition that deterrence must be tailored to the unique goals, values, and culture of specific adversaries.

This definition accounts for the likelihood that an adversary considers more than just the costs associated with an action they are contemplating. They compare the costs of a course of action to the benefits they seek, while also examining the consequences if they do not act. If an adversary believes that the costs associated with an action are credible and will be incurred, deterrence may still fail if the adversary perceives that the consequences of restraint are greater. This approach implies that deterrence strategies consider adversary perceptions of both the costs and benefits of a course of action, as well as their perceptions of the costs and benefits of restraint.

INSIGHTS RELEVANT TO THE RISKS OF NUCLEAR WAR

There are many complex ideas about risks associated with nuclear deterrence, both in theory and in practice. The literature is vast5 but four ideas about nuclear risks have been especially influential, sometimes misunderstood, and sometimes ignored in practice: the reciprocal fear of surprise attack, the threat that leaves something to chance, the commitment trap, and the risk of inaction. They remain essential for proper understanding of nuclear risks.

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5 Important efforts to review this vast literature on nuclear deterrence theory and strategy include Freedman (2003) and Tetlock et al. (1989, 1991).

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

The Reciprocal Fear of Surprise Attack

Nuclear war between two states could be initiated out of “the dynamics of mutual alarm,” even though neither planned nor desired to initiate a nuclear conflict (Schelling 1980, 2008). In this case, both governments prefer avoiding nuclear war, but both fear that the other might strike first and that the consequences of striking first are preferable to striking second. If war is deemed imminent and preemption is a preferred option, Schelling argued, each state might increase its nuclear alert level for the sake of deterrence, but each might also fear that such actions mean that the other was preparing for a surprise attack. Schelling’s original model included a state placing extra (potentially less reliable) warning systems on alert as the fear of surprise attack increased. This would reduce the risk of a false confirmation that no attack was being launched (false negative) but increases the probability of a false warning of attack (false positive).

During the early Cold War, the Truman administration studied and then rejected the option of initiating a preventive war against the Soviet Union, but it maintained the option of launching a preemptive strike if a Soviet attack was deemed imminent and unavoidable (Truman and Lay 1950). However, because the United States could not be certain that it would receive accurate warning of an imminent Soviet attack and Cold War nuclear war plans, the administration’s approach included both preemptive and retaliatory military options (Lynn 1969; Sagan 1987).

The dangers associated with mutual fears of preemption were highlighted during the 1962 Cuban missile crisis when a U.S. U-2 spy plane accidentally flew into Soviet airspace (Sagan 1993). Although neither the Russian nor the U.S. government has ever officially forsworn the option of a preemptive nuclear attack, both know that the other side’s nuclear forces would largely survive an attack and both have invested heavily in redundant and (hopefully) independent and reliable warning systems.

But these mitigating factors may not exist in other conflict scenarios against new nuclear states. An example is the January 2018 incident in which a false warning of a North Korean missile attack was announced in Hawaii. The U.S. government did not overreact because redundant sensors reported that no attack was under way, professional warning system officers immediately reported that they had made a mistake, and U.S. officials did not believe that North Korea was likely to attack Hawaii. But it is instructive to imagine if this false warning incident had occurred in North Korea instead of the United States. None of the three mitigating factors would be as strong because North Korea’s missile warning system is dependent on radars and has less redundancy, its officers might be less willing to acknowledge errors because the consequences of such acknowledgment could cost them more

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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than just their livelihoods, and it could be perceived that a U.S. nuclear attack was likely given then-recent statements from President Donald Trump (Sagan 2018).

The Threat That Leaves Something to Chance

A threat that leaves something to chance is a strategy centered on making a credible threat of a nuclear first use in a situation that might otherwise be deemed unlikely to be implemented, such as responding to a conventional attack on an ally (Schelling 1960). Schelling provided two metaphors that helped illustrate the idea. First, while no individual could rationally threaten to jump off a cliff, the individual could rationally come closer and closer to the cliff and deliberately increase the chance of slipping off. Second, in the case of a fighter jet deliberately buzzing an adversary’s fighter coming close to its border, the pilot was not threatening to deliberately crash into the enemy’s plane; they were threatening to “accidentally” crash into it by losing control as they came closer. Such manipulation of risk was, Schelling argued, a core strategy of brinkmanship.

One application of this concept was the forward deployment of U.S. nuclear forces into NATO allies’ territory. The idea was that such deployments would make extended deterrent commitments more credible even if a U.S. president might not want to use nuclear weapons in response to a conventional attack.

The danger of the threat that leaves something to chance is precisely that it leaves something to chance. Presidents since Kennedy have been reluctant to delegate nuclear launch authority to local commanders. After the Cuban missile crisis, locking devices were placed on U.S. nuclear weapons to reduce the risks of any unauthorized use of such weapons.

Delegation authority may exist in other nuclear states, however. Vipin Narang (2010, p. 87), for example, argues that in Pakistan, “lower-level officers may be ceded some authority, particularly as a crisis unfolds, to assemble and release Pakistani nuclear weapons should circumstances require it.” This contributes, Narang argues, to an asymmetric escalation posture in which negative controls are “likely circumventable, by design, for deterrence purposes in a crisis or conflict situation with India” (Narang 2010, p. 90).

The Commitment Trap

The central idea of the commitment trap is that deterrent threats might not reflect existing commitments to use nuclear weapons, but rather create increased likelihood of nuclear use in the event of deterrence failure by linking the deterrent threat to a president’s or the nation’s reputation for honoring commitments (Sagan 2000). One example of this phenomenon occurred during the Cuban missile crisis. President Kennedy stated that the United States would act if Cuba should possess

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

a capacity to carry out offensive action against the United States. He later believed that his earlier public warning boxed him into rejecting a diplomatic solution and into choosing a more serious military response (Bundy and Rosenblum 1989).

Experts hold a range of views about whether threats of nuclear response contributed to Saddam Hussein’s decision not to use chemical or biological weapons in 1991. The U.S. Strategic Command’s Essentials of Post–Cold War Deterrence report, for example, argues that this use of calculated ambiguity worked to deter Saddam Hussein (U.S. Strategic Command 1995). After examining the captured Iraqi records, however, independent scholars argued that Saddam Hussein never intended to use chemical weapons against U.S. troops on the battlefield; instead, he saw his chemical arsenal as a strategic deterrent to the United States and Israel nuclear threat (Buch and Sagan 2013).

The Risk of Inaction

The risk of inaction is poorly understood in much writing about deterrence. President Kennedy stated during the Cuban missile crisis that the risk of war with the Soviet Union was between one-third and one-half (Kennedy 1999). While President Kennedy’s blockade of Cuba and threat of an attack if the Soviets did not remove the nuclear-armed missiles increased the risk of war, it is possible that the risks of a nuclear war might have been even greater in the future if the missiles remained in place. Not taking an action also entails risks.

THE HISTORY AND LITERATURE OF RISK ASSESSMENT FOR NUCLEAR TERRORISM

Risk assessments of nuclear and radiological terrorism have been conducted for many years, and the approaches and methods that have been used have evolved as threats of terrorism (and understanding of them) have changed. This overview includes a brief timeline of major events related to nuclear terrorism and the types of analyses that were produced to guide policy or decisions. While the literature presented in this report is U.S. centric, it is important to note that the literature from other countries and regions represents other historical experiences and strategic decisions.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Early Years (mid-1940s and 1950s)

Almost from the dawn of the nuclear age, there have been concerns over the possibility of covert emplacement of nuclear explosives.6 In a 1946 congressional hearing, J. Robert Oppenheimer noted the feasibility that components of a nuclear bomb could be smuggled and then successfully detonated in a major city like New York. The Atomic Energy Commission (AEC)7 then commissioned a study to assess detection capabilities against this threat (Lüth 2013; Richelson 2009). The threat of concern at that time was not of terrorist groups but of Soviet Union operatives placing such a bomb in a large city (Bunn et al. 2016; Zenko 2006).

Similarly, the first serious considerations of possible attacks on nuclear reactors focused on the possibility that national adversaries, such as communist countries, might attack them, not terrorist groups. For example, during the 1957 licensing process for the Turkey Point nuclear power reactor in Florida, opponents expressed concern that the reactor’s proximity to Cuba would make it vulnerable to attack (Ramberg 1985; Travers 2001).

The 1960s

The concern about the origin of the threat shifted in the 1960s. A 1967 report to the AEC (Lumb et al. 1967) expressed concern that terrorists could acquire plutonium or highly enriched uranium and use these materials to make a crude nuclear bomb. The report recommended that safeguards and security programs “be designed in recognition of the problem of terrorist or criminal groups clandestinely acquiring nuclear weapons or materials useful therein” (Lumb et al. 1967, p. 331). The AEC responded with the first-ever rules requiring private owners of nuclear material to provide security for that material.

These early assessments of the risks and of the adequacy of security arrangements for nuclear weapons, materials, and facilities were largely based on expert judgment, not on systematic risk assessment approaches. Methods were largely speculative, based on imagining what adversaries might attempt to do and steps that could be taken to block those imagined pathways (Hirsch et al. 1986; Lumb et al. 1967; Ramberg 1985; Travers 2001).

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6 For summaries of portions of this history, see Bunn (2013), Bunn et al. (2016), Desmond et al. (1997), Richelson (2009), and Walker (2001).

7 The AEC was responsible for designing and producing nuclear weapons, as well as encouraging the use of nuclear power and managing its safety regulations. The Energy Reorganization Act of 1974 transferred the regulatory functions of the AEC to the new Nuclear Regulatory Commission (NRC), and a few years later the Department of Energy was created to encourage the use of nuclear power and to manage the U.S. nuclear weapons.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

The 1970s

By the 1970s, both public and government concern about the danger of nuclear terrorism had increased, driven by the rise of international terrorism following the 1967 Arab–Israeli war and increased threats to nuclear facilities. The 1972 attack at the Munich Olympics demonstrated that well-trained and well-armed terrorists could successfully carry out an assault in a modern developed country. Within the United States, hijackings and other terrorist-like incidents increased and were well publicized, including multiple nuclear threats and hoaxes (Bunn et al. 2016; Richelson 2009). Later, the Three Mile Island nuclear reactor accident in 1979 further focused the public’s attention on nuclear risks.

The AEC commissioned an additional study of the adequacy of security arrangements, which concluded that existing security arrangements for nuclear material needed urgent improvement. Furthermore, the authors called for a design basis threat, which led to a new approach that is still in place today for assessing the adequacy of physical security measures at nuclear power facilities.8

These concerns provoked major changes in U.S. nuclear security requirements (Bunn 2013; Walker 2001). Still, others argued that terrorists would reject the level of violence that a nuclear attack would produce as it would not serve their political objectives (Bunn et al. 2016; JAEIC 1976).

During the 1970s, a variety of additional methods came into use for assessing aspects of the risks of nuclear terrorism and nuclear safety. The AEC and the new Nuclear Regulatory Commission (NRC) began applying systems engineering approaches to design and assess security systems in what came to be known as the design evaluation process overview. In 1975, the NRC issued the Reactor Safety Study, which was the first full-scale use of probabilistic risk assessment to quantify the risk of a nuclear reactor accident due to possible equipment and unintentional human failures. Assessments of the risk of sabotage of nuclear reactors also began to use insights from early probabilistic risk assessments.

The 1980s

The 1980s saw somewhat reduced public and government attention to the risks of nuclear terrorism and little change to the threat assessments of the 1970s. Cold War tensions in the early 1980s and the 1986 Chernobyl nuclear accident focused attention instead on the dangers of nuclear war and on nuclear accidents.

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8 Earlier, the WASH-740 report (AEC 1957) had identified major uncertainties in the scientific knowledge basis for evaluating the consequences of major nuclear reactor accidents. Coincidentally, in 1975 the Reactor Safety Study (known as WASH-1400 [NRC 1975]) used risk assessment methods for the first time to estimate the risks of an accidental exposure to members of the public due to a nuclear power station accident.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

Nevertheless, congressional investigations of security for U.S. nuclear facilities continued, the executive branch remained concerned because of both security failures at U.S. facilities and continuing terrorist attacks around the world, and some private analysts remained quite concerned (Leventhal and Alexander 1987).

The 1986 national intelligence estimate, The Likelihood of Nuclear Acts by Terrorist Groups, concluded, as had the 1976 and 1977, that a few terrorist groups were capable of making a nuclear bomb but behavioral constraints made it unlikely (Director of Central Intelligence 1986). This view of the problem, which was reached largely through analysis of the historical record and of imputed terrorist incentives, held for much of the next decade and a half.

The 1990s

The collapse of the Soviet Union in 1991, and the social, political, and economic disruptions that followed, led to problems with security for nuclear weapons, materials, and facilities in the former Soviet states. There were multiple well-documented thefts of kilogram quantities of highly enriched uranium or separated plutonium. U.S. intelligence concluded that nuclear facilities in the former Soviet Union did not have adequate safeguards and security (Allison et al. 1996; Bukharin 1996; Bunn 2000).

Concerns over “loose nukes” were exacerbated by increasingly violent terrorist actions. In Japan, the terror cult Aum Shinrikyo, which carried out nerve gas attacks in the Tokyo subway system, had also pursued both nuclear and biological weapons. Osama bin Laden’s al-Qaeda group bombed the U.S. embassies in Kenya and Tanzania in 1998, sought nuclear weapons, and announced that it was their religious duty to acquire weapons of mass destruction (Daly et al. 2005; Danzig et al. 2012).

The United States responded with counterterrorist efforts against al-Qaeda and other groups, and a program to help secure nuclear weapons and materials in the former Soviet states (National Research Council 1999, 2009).

The 2000s and Beyond

The 2000s and beyond saw further shifts in terrorist threats, nuclear security, and refinements of assessment methods. Assessments of the threat of nuclear and radiological terrorism were fundamentally transformed by the 9/11 attacks in the United States. These attacks demonstrated that some terrorist groups were, in fact, seeking to cause catastrophic loss of life. Moreover, they showed that coordinated attacks involving multiple trained teams, prior collection of intelligence and specialized training, and a willingness to die as part of the plan were realistic threats

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

(Ezel et al. 2010; Merrick and Parnell 2011; Parnell et al. 2011; Rosoff and von Winterfeldt 2007; Willis et al. 2005).

Investigations after the 2001 attacks revealed far more about al-Qaeda’s nuclear, radiological, chemical, and biological efforts than had previously been known. Terrorists working with al-Qaeda also considered attacks on nuclear reactors and the use of radiological dispersal devices, though the unclassified literature does not make clear how far those efforts proceeded (Mowatt-Larssen and Allison 2010; Tenet 2007). In addition, North Caucasus terrorists (Chechens and others) reportedly pursued nuclear or radiological weapons, according to the Russian state newspaper, Rossiskaya Gazeta, which also separately reported additional cases of terrorist reconnaissance on nuclear weapon transport trains.

In response, the U.S. government increased security requirements for both government and commercial nuclear facilities, as did a number of other countries (GAO 2004a,b). The United States implemented changes to further protect nuclear facilities, including nuclear weapons storage/handling sites under the Department of Defense, nuclear weapons complex facilities run by the Department of Energy, and commercial nuclear facilities licensed and regulated by the NRC. Box 3-1 provides a description of NRC-regulated security requirements for commercial nuclear facilities; the Department of Defense and the Department of Energy have similar security requirements and protocols in place for their respective facilities that handle nuclear weapons and nuclear materials.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

During the 2000s, the government also created the Department of Homeland Security (through the Homeland Security Act, P.L. 107-296) in 2002 and the Domestic Nuclear Detection Office in 2005 to coordinate U.S. federal efforts to detect and protect against nuclear and radiological terrorism) (DHS 2021; Gaertner and Teagarden 2006; Helfand et al. 2002).9

The heightened concern also led to a flurry of international activity related to preventing nuclear terrorism. The IAEA launched a new nuclear security fund to finance expanded IAEA nuclear security programs. In 2002, less than a year after the 9/11 attacks, the leaders of what was then the Group of Eight launched the Global Partnership Against the Spread of Weapons and Materials of Mass Destruction, in which the participants pledged to invest $20 billion over 10 years in cooperative activities for threat reduction activities (NTI 2002). In 2004, the United Nations (UN) Security Council unanimously passed Resolution 1540, which legally obligated all member states to criminalize any help to terrorists with weapons of mass destruction and to create security and accounting for any nuclear, chemical, or biological weapons or materials those states might have (UN Security Council 2004). In 2005, an amendment was made to the UN physical protection convention to extend the convention’s coverage from civilian nuclear material in international transport to civilian material in domestic use and to include sabotage. The convention entered into force in 2016.10 The same year, the Russian-proposed International Convention on the Suppression of Acts of Nuclear Terrorism was opened for signature (Perera 2005). In 2006, Russia and the United States jointly launched the Global Initiative to Combat Nuclear Terrorism (DOS 2009; National Research Council 2002).

After the deaths of key al-Qaeda leaders, including Osama bin Laden in May 2011, the United States determined al-Qaeda’s capability to launch catastrophic attacks on the United States to have been substantially reduced (Office of the Coordinator for Counterterrorism 2012). Nevertheless, al-Qaeda operations continued and still continue in a number of countries, and many of the identified participants in al-Qaeda’s nuclear effort remain at large. Moreover, the violent jihadist movement continues to spread. The Islamic State, originally an off-shoot of al-Qaeda, is an important example of a rapidly evolving threat: it was not mentioned in the 2014 U.S. intelligence community’s annual assessment of threats to the country. But by June 2014, the group had seized much of Iraq and Syria and declared a global caliphate. While the Islamic State’s geographic caliphate has since been destroyed,

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9 In 2018 the Domestic Nuclear Detection Office was combined with the Office of Health Affairs into the Countering Weapons of Mass Destruction Office.

10 See International Atomic Energy Agency, “Convention on the Physical Protection of Nuclear Material (CPPNM) and its Amendment,” https://www.iaea.org/publications/documents/conventions/convention-physical-protection-nuclear-material-and-its-amendment.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

the group continues to have followers operating in many countries, and it still has access to substantial resources.

Between 2010 and 2016, efforts to strengthen nuclear security around the world accelerated with a series of global nuclear security summits, which helped focus attention and accelerate various actions, such as removal of nuclear material from vulnerable sites (Cann et al. 2016). However, U.S.–Russian cooperation on nuclear security was almost entirely terminated after Russia’s 2014 annexation of Crimea (then part of Ukraine), leaving little remaining communication between the countries with the world’s two largest nuclear complexes (Bunn and Kovchegin 2018).

During this period, methods for assessing aspects of the risks of nuclear and radiological terrorism progressed slowly. There were enhanced efforts to model the economic and social effects of a nuclear or radiological attack, using both economic models and agent-based modeling (Chandan et al. 2013; Vargas 2020; Vargas and Ehlen 2013), as well as efforts to model and test the performance of nuclear security systems in the face of intelligent adversaries. The Department of Homeland Security and Domestic Nuclear Detection Office explored risk analysis to guide decisions (Streetman 2011), but most of the methods pursued were refinements of methods already applied in the 2000s.

The Fukushima Phase 2 report (NASEM 2016) allowed that adversarial intent could be included in risk assessments. This was a notable shift from earlier consensus reports from the National Academies of Sciences, Engineering, and Medicine, which had largely concluded that modeling adversarial intent using such risk assessment methods as probabilistic risk assessment was not feasible (National Research Council 2006, 2011, 2013).

One new assessment effort was the Nuclear Threat Initiative’s Nuclear Security Index, published every 2 years starting in 2012.11 The index uses a variety of indicators of the status of areas, ranging from security and control measures at individual sites to risk environment, to give an overall rating on how countries are doing on nuclear security. The countries’ ratings determine their ranking.

The International Picture

Since the 2001 terrorist attacks in the United States, some other governments have shared a substantial level of concern about nuclear terrorism. For example, Norway (Karamoskos 2009), Canada (Etchegary et al. 2008), and Australia (Gaidow 2007; Hirst 2007) have explored public perceptions of the risks and the impact of the 9/11 attacks to national security. Counterterrorism activities and efforts to improve security for nuclear weapons, materials, and facilities and to stop nuclear smuggling have been global initiatives.

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11 For more information, see the NTI Nuclear Security Index website at https://www.ntiindex.org.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×

Russia, in particular, made efforts to reduce the threat of nuclear terrorism. The country first proposed the nuclear terrorism convention, and they joined with the United States in launching the Global Initiative to Combat Nuclear Terrorism in 2006. These programs have worked to improve how detection of material out of regulatory control is communicated and addressed among law enforcement agencies and governments and to test physical security measures and responses to possible terrorist events.

IAEA efforts that focused on nuclear security expanded dramatically after the 9/11 attacks. IAEA’s small Office of Physical Protection became the Office of Nuclear Security, which has now become the Division of Nuclear Security, funded at tens of millions of dollars a year. IAEA expanded its review services, launched a nuclear security series of documents, greatly expanded its training programs in nuclear security, and increased its efforts to collect and analyze various types of data, from incidents to program implementations. In particular, IAEA now offers guidance on assessment methodologies for physical protection of nuclear facilities and implementation of radiation detection to counter nuclear smuggling. However, there is no international agreement on methods for assessing the threat of nuclear and radiological terrorism.

INSIGHTS RELEVANT TO THE RISKS OF NUCLEAR TERRORISM

As with nuclear war, there are fortunately few data on actual cases of nuclear terrorism to draw from. Nevertheless, there is a great deal of data on terrorism more generally, and some data on past terrorist attempts to acquire nuclear weapons, make radiological dispersal devices, or sabotage nuclear facilities. These three categories of activity involve different levels of violence and immediate effect, have different levels of technological complexity, and may have different theoretical implications. The discussion below focuses primarily on the most extreme form of nuclear or radiological terrorism: the actual use of nuclear explosives.

Several key insights relevant to assessing the risks of nuclear terrorism have been drawn from the broader set of data on terrorist activities over the decades. These insights relate to terrorist motivation, technical ambition and capability; the factors affecting the availability of nuclear weapons and materials; and the chances that states might choose to help terrorists get nuclear explosives. Although experience and the theoretical literature help explore kinds of groups that may be interested in nuclear violence, terrorist groups are varied and ever changing. The following insights should be considered tendencies and not absolute rules.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Terrorist Motivations: No Longer Just “A Lot of People Watching”

The understanding of terrorist motivations has evolved over recent decades. Analysts exploring the motivations of different terrorist groups have identified the following types of groups that may be inclined toward mass slaughter (Ferguson et al. 2005):

  • Nihilist groups, interested in destruction for its own sake;
  • Millennial groups, who envision the end of the world and want to help hasten it (such as Aum Shinrikyo); and
  • Groups with extreme objectives, such as taking down a superpower or achieving world domination, for which weapons of extraordinary power might seem appropriate (such as al-Qaeda and the Islamic State).

Many advanced democracies are coping with increasing right-wing extremism. Some of these groups and individuals appear to fall into the “extreme objectives” category and have been focused on nuclear themes. The Turner Diaries, a novel that is a foundational text for racist extremists in the United States, envisions using nuclear weapons against U.S. cities to bring down the prevailing multiracial society and establish a white supremacist state. The manifesto written by Anders Breivik, the terrorist who massacred students and bombed the parliament in Norway, explores nuclear themes at length, including a detailed discussion of sabotaging nuclear facilities. One neo-Nazi extremist group in the United States even named itself the “Atomwaffen Division” (see, e.g., Earnhardt et al. 2021).

Deterring Terrorists and Terrorist Deterrence

Although it is not obvious that a terrorist group that acquired a nuclear bomb would immediately choose to use it (Dunn 2005), history makes clear that terrorist groups are difficult to deter. However, many types of terrorist groups can be, and have been, deterred from taking some types of terrorist actions. When groups have territory and populations they control, or for whom they are fighting, they may be motivated to avoid actions that could provoke retaliation on those populations. Some analysts have argued that if terrorists did get a nuclear bomb, it would serve their interests better not to detonate it, but to hold it to deter attacks against them. In a 1999 interview, Osama bin Laden claimed that al-Qaeda had nuclear and chemical weapons as a deterrent that it would use in retaliation for nuclear or chemical attacks against Muslims (Dunn 2005). However, the existence of such terrorist weapons would likely provoke a global effort to find and eliminate them.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Terrorist Technical Ambitions: “Sticking with the Tried and True”

Another relevant set of analyses has focused on the weapons terrorists use. The overwhelming majority of terrorist groups focus on conventional weapons. Recently, some terrorist attacks have been even simpler, using vans or cars driven into crowds, for example. Analysts have noted that terrorists, facing the constant possibility of being caught, typically want to carry out actions with a high chance of success—or at least of getting far enough to be very visible and provoke fear (Jenkins 2008). Using challenging new types of weapons that may take a long period to figure out and may not work have not typically been something most terrorist groups have pursued.

Nevertheless, some terrorist groups have actively attempted to develop nuclear, biological, and chemical weapons, including Aum Shinrikyo and al-Qaeda. There is little publicly available evidence of a focused nuclear weapons effort by the Islamic State, but it did manufacture and use its own chemical and conventional weapons and carry out a rapid program of testing and improving its drones for bomb delivery (see, e.g., Gartenstein-Ross et al. 2019; Tønnessen 2017).

Making nuclear explosives requires not only the factual knowledge that can be conveyed in written documents, but the tacit knowledge that comes only with prior experience. Because terrorist groups will not typically have anyone with prior experience making nuclear weapons, it is argued, they would have difficulty producing a nuclear bomb (Ouagrham-Gormley 2007). But it should be recalled that repeated government studies have concluded that it is plausible that a sophisticated terrorist group could make a crude nuclear bomb; in the case of highly enriched uranium, the technical requirements are straightforward; and states have almost always succeeded in their very first nuclear test, even when they had no personnel with prior tacit knowledge available to help.

Terrorist Capabilities for Complex, Long-Term Projects: “The Terrorist’s Dilemma”

Many terrorist groups have had trouble organizing complex, long-term projects in part because of the constant possibility of being interrupted by counterterrorism forces. Shapiro (2013) identified the terrorist’s dilemma: on one hand, in order to maximize their perceived chance of accomplishing their group’s objectives, leaders of a terrorist group need to communicate with their operatives and convince them to carry out the activities the leadership thinks will contribute to the cause and avoid the activities the leadership thinks will undermine the cause; on the other hand, all communications and gatherings of leadership and operatives increase the chance of being detected and stopped by counterterrorism forces. Terrorist leaders,

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Shapiro argues, must constantly balance these concerns, and this constrains how terrorist organizations are managed.

In most cases, a nuclear bomb project would require recruiting technical experts and weeks, months, or years of work. The leadership of the group may not need to get involved in day-to-day management of the effort, but it likely needs to provide resources and keep the people motivated and working overtime. Thus, such efforts might well run up against the kind of dilemma Shapiro identified.

CONCLUSION

CONCLUSION 3-1: The U.S. nuclear posture has evolved over time, taking into account new threats, developing deterrence strategies against different U.S. adversaries, technological advancements, nuclear arms reductions, and changing geopolitical environments. U.S. assessments of the risks of nuclear terrorism have likewise evolved over time, taking into account the new threats and emerging technologies.

Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Page 33
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Page 34
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 35
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 36
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 37
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 38
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 39
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 40
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 41
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
×
Page 42
Suggested Citation:"3 The History and Literature of Risk Assessment for Nuclear War and Nuclear Terrorism." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism. Washington, DC: The National Academies Press. doi: 10.17226/26609.
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Page 43
Next: 4 The Use of Risk Assessment for Nuclear War and Nuclear Terrorism »
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 Risk Analysis Methods for Nuclear War and Nuclear Terrorism
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The assessment of risk is complex and often controversial. It is derived from the existence of a hazard, and it is characterized by the uncertainty of possible undesirable events and their outcomes. Few outcomes are as undesirable as nuclear war and nuclear terrorism. Over the decades, much has been written about particular situations, policies, and weapons that might affect the risks of nuclear war and nuclear terrorism. The nature of the concerns and the risk analysis methods used to evaluate them have evolved considerably over time.

At the request of the Department of Defense, Risk Analysis Methods for Nuclear War and Nuclear Terrorism discusses risks, explores the risk assessment literature, highlights the strengths and weaknesses of risk assessment approaches, and discusses some publicly available assumptions that underpin U.S. security strategies, all in the context of nuclear war and nuclear terrorism.

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