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Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
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2
Risk Analysis

Risk analysis aims to systematically identify the pathways from present circumstances to future outcomes, and the likelihood of negative consequences occurring. To be reliable, the analysis must include a realistic—and in principle complete—description of all the ways that the current state can lead to those future outcomes of concern. Such an analysis requires consideration of future outcomes, some of which may be hypothetical. It is especially difficult for situations for which there is little or no direct experience—nuclear war and nuclear terrorism being cases in point.

Risk analysis, performed well, encourages participation between those requesting the analysis and those conducting it. The process also helps to inform leadership of the decisions, options, and timelines that can be expected if a harmful event occurs. The principles of a well-conducted risk analysis are outlined in Box 2-1. The risk analysis results can aid in prioritization of different decision outcomes; for example, identifying pathways that are most likely to be more harmful, which therefore must be avoided or mitigated even if at great effort. Additionally, identifying the pathways provides the basis for training and preparation to avoid, minimize, or mitigate the failure modes.

Box 2-1 highlights the importance of characterizing and assessing uncertainties in a well-done risk analysis using scenarios to both span potential outcomes and understand dependencies. One of the challenges in making decisions related to avoiding nuclear weapons use (and its risks) or nuclear terrorism is due to the sparsity of direct experience or statistical evidence and the corresponding large uncertainties.

In some risk analyses, relevant statistical data bases exist from which one can calculate probabilities (i.e., frequencies of occurrence) for use in the risk assessment. When relevant statistical samples and probabilities based on frequencies in such samples are limited, Bayesian approaches that utilize conditional probabilities can aid in developing risk analysis. Even if data samples exist, Bayesian approaches can help the risk analyst account for additional information that is known about the system (e.g., information gathered from expert opinions, models, and surrogate data from similar situations) and also reflect aspects of the scenario that may evolve with time (e.g., changes in the adversary, technology, or operations). The probability of a scenario can then be computed as a series of conditional probabilities reflecting the scenario description (see NASEM, 2023, Chapters 5 and 6). That assessment captures the dependencies among events, through conditional probabilities.

The same Bayesian logic can be used to assess the analyst’s beliefs about a future risk given new available information, which could include false positives (i.e., a “false alarm”) or false negatives (i.e., a missed warning or signal). Both types of errors have to be included in the updating of the probability to assess the value of that information as the possible improvements of the decision. This computation allows accounting for the uncertainties both in the events a priori, and in the information, which can be correct but can also include false positives or simply not include signals when it should (false negatives). That logic allows assessing the value and validity of information of a message, which may allow improving a decision involving uncertain events.

Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×

The 2013 report of the Institute of Medicine, Environmental Decisions in the Face of Uncertainty, identified types of uncertainties associated with risk analysis to aid decision making within the Environmental Protection Agency. The report suggests that scenario development be used for events for which little or nothing is known about the event’s impact or likelihood to aid decision makers and risk analysts (IOM, 2013). An example of one such a situation is climate change. The Intergovernmental Panel on Climate Change has developed and regularly updates a set of possible scenarios. The aim of the scenarios is not to predict the future but to assess the uncertainties linked to possible climate and socioeconomic futures, which can inform decisions (IPCC, 2022).

FINDING 2-1: Risk analysis, when conducted well, can provide a systematic and disciplined approach; illuminate threats, vulnerabilities, and consequences; and analyze complex interactive situations and dependencies among events. Good risk analysis has leadership guidance and support, informs leadership, and includes scenarios and exercises.

FINDING 2-2: Those in charge of developing policy or strategy ought to be made aware of how risk methods could improve options to mitigate risks of nuclear weapons use or nuclear terrorist attacks especially at a time when those risks are rapidly evolving.

FINDING 2-3: A well-performed risk analysis is decision focused, explicit about objectives, incorporates creative alternatives, addresses relevant outcomes, characterizes uncertainties through development of scenarios and exploration of dependencies, addresses changes to risks over time, and supports transparent discovery and policy deliberation. These define, in part, fundamental principles of risk analysis.

Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×

Important details of each of these components are listed in Box 2-1.

CONCLUSION 2-1: The benefit of a well-performed risk analysis is that it prompts those requesting the analysis, who may have decision-making biases, to work in conjunction with those conducting the risk assessment to develop, for example, a systematic listing of potential outcomes; the pathways that can lead to those outcomes; and underlying assumptions, including correlations (dependencies) between different paths and outcomes.

U.S. GOVERNMENT RISK ANALYSIS METHODS

The committee collected information relevant to its tasking in classified meetings held over 7 months. A full list of the presenters and their affiliations can be found in Appendix C. Throughout its information collection efforts, the committee searched for examples of risk assessment methods (Who is doing what?) and how their results were used to develop strategy and guide policy and decisions. Three specific risk analysis efforts are described in this chapter.

Differences in Nuclear War and Nuclear Terrorism Risks

Nuclear war and nuclear terrorism risk methods are distinct in important ways. The risk of nuclear war is often assessed by considering nuclear armed adversary decision calculus, while the risk of nuclear terrorism is most often focused on the availability of nuclear materials that might be used by a non-state actor or state-sponsored terrorist group to obtain a nuclear device or to construct an improvised nuclear device or a radiological dispersal device.6 Two forms of deterrence come into play for both war and terrorism: the power to hurt (i.e., retaliation) and the power to deny (i.e., preventing an adversary from achieving objectives through either defenses or prevention of their capabilities).

For policy analysts and senior decision makers, the threats posed by other nation states with nuclear weapons often drives decision making in documents such as the Nuclear Posture Review. The Obama administration’s commitment to modernizing the U.S. nuclear deterrent forces accompanying Senate ratification of the 2010 New START Treaty is a good example. Estimating the potential threat posed by a nuclear armed adversary’s capabilities is as critical as examining the impact of U.S. responses to that threat, and identifying military threats and diplomatic assurances that could lead to avoiding or ending a nuclear conflict on acceptable terms to reduce further escalation.

In contrast, decision makers in the nuclear terrorism arena are often more focused on nuclear materials attractiveness, availability, and quantity (e.g., based on assessments of the effectiveness of security measures to protect nuclear materials). These assessments can guide considerations of where to focus U.S. non-proliferation and nuclear material security assistance programs and dollars. Furthermore, the role of a nuclear nation-state actor distinguishes programmatic decisions in the nuclear terrorism field from those facing decision makers concerned about nuclear deterrence and nuclear war.

FINDING 2-4: To deter nuclear terrorism, the United States has focused on minimizing access to nuclear materials (i.e., the power to deny access), but state-sponsored terrorism can also be deterred by the power to hurt (i.e., threat of punishment once attributed). Nuclear war deterrence is broader and includes deterrence by denial of adversary objectives through U.S. resilience and the threat of a U.S. response that imposes expected costs that are clearly higher than expected benefits of nuclear use (i.e., the power to deny and destroy).

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6 The Phase I report addressed the scenarios (Chapter 2), history and literature of risk assessment (Chapter 3), and the use of risk assessment for nuclear war and nuclear terrorism (Chapter 4). These three chapters also highlight the differences between the risk of nuclear war and nuclear terrorism.

Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×

EXAMPLES OF RISK ANALYSIS METHODS WITHIN THE U.S. GOVERNMENT

The committee highlights three methods for assessing nuclear risks or risks associated with nuclear use that are being conducted within the U.S. government.

Defense Threat Reduction Agency Nuclear Consequence Models

Consequence is one part of a traditional risk equation. The Defense Threat Reduction Agency (DTRA) maintains the Department of Defense’s (DoD’s) nuclear war consequence models, which are used across DoD and therefore have a large impact on DoD’s strategic thinking on nuclear war. In the committee’s Phase I report, the committee outlined the effects of a nuclear explosion by its immediate, near-, and long-term effects (NASEM, 2023):

The Immediate effects of a nuclear explosion include an intense burst of gamma and neutron radiation; a fireball (anything inside the fireball is likely to be totally consumed); an intense, blinding flash and a pulse of thermal radiation (causing burns and igniting fires); a powerful blast wave, accompanied by intense winds; and an intense electromagnetic pulse (localized for blasts within the atmosphere, but more far-reaching for blasts in space). (p. 52)

Near- and long-term effects are wide reaching. In the near term (roughly, 1 hour to 1 week after the event), widespread evacuations and grid instability are possible along with initial radiation effects on humans. In the long term (weeks to several months or years after the event), effects include social and economic unrest, political and governance crises, health effects, infrastructure failures, negative environmental and climate effects, migration, and psychological distress. (p. 52)

Updating our Cold War understanding of blast damage in a modern city is another important area of research. The bombings of Hiroshima and Nagasaki demonstrated that the area of glass breakage is nearly 16 times greater than the area of significant structural damage. Injury from broken glass has not previously been well modeled, however, because cold war planners generally considered it not of military significance. (p. 54)

[E]arly studies show that some researchers (and funders) recognized the importance of and were beginning to explore the social and psychological effects of nuclear war. It is noteworthy and disturbing that there has been so little attention to further deepening understanding of these vital impacts since 1986. (p.55)

In its briefing to this committee, DTRA confirmed that their nuclear effects categorization and scope is similar.

FINDING 2-5: Within DoD, DTRA provides estimates of the impact of nuclear weapons. The consequence assessment is focused on prompt effects and military objectives. This results in a partial accounting of the consequences leading to a limited understanding of the breadth of the outcomes.

CONCLUSION 2-2: Current modeling by DoD’s DTRA of the consequences of nuclear explosions resulting from strategic deterrence failure are limited to prompt military effects, especially detonation (blast) and some fallout effects, and does not extend to broader and longer-term effects. This information further supports this committee’s Phase I Conclusion 4-1, that there is a need to improve the understanding of the physical effects of nuclear weapons (e.g., fires, damage in modern urban environments, electromagnetic pulse effects, and climatic effects, such as nuclear winter), as well as the assessment and estimation of psychological, societal, and political consequences of nuclear weapons use.

Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×

Risk of Strategic Deterrence Failure

U.S. Strategic Command (USSTRATCOM) Risk of Strategic Deterrence Failure (RoSDF) is a recently developed, formalized, qualitative tool that assesses the estimated impact of diplomatic, informational, military, and economic factors on the risk of deterrence failure. Within RoSDF, “adversary decision calculus” is a method cited to assess an adversary’s goals, psychology, cultural perspective, information, and reasoning (USSTRATCOM, 2021). Adversary decision calculus is within USSTRATCOM’s RoSDF as well as by the Joint Staff (J5). The method can guide U.S. actions to maximize deterrence; adversary’s responses are closely monitored after actions are taken by the United States such as commencing military exercises, verbal statements made by U.S. officials, or alerting U.S. forces.

However, adversary decision calculus has important weaknesses. Some of these were discussed in the Phase I report (NASEM, 2023). One basic weakness is the contrast with scenario-based methods that are highlighted earlier in this chapter. Scenario-based methods force more attention to interactive behavior and other dependencies that influence potential outcomes.

Risk of Nuclear and Radiological Terrorism

The Department of Homeland Security’s (DHS’s) Science and Technology Directorate (S&T) is responsible for developing and maintaining the capability to perform terrorism risk assessments of weapons of mass destruction tailored to a variety of different users (DHS, 2021). DHS uses probabilistic risk assessment methodology to assess risk that uses a set of scenarios with data derived and modeled probabilities and consequences. Risk assessments are scaled to user requirements and can be used to address components of overall risk, or they can be used to assess the overall risks of a nuclear, radiological, chemical, or biological attack on the United States.

Another key aspect of DHS’s risk assessment effort is its interface with the consumers of these assessments:

Development of the risk assessments has been an ongoing, community-driven process so as to ensure that the methodology and resultant outputs adequately address the needs of the Homeland Security Enterprise (HSE) and interagency stakeholders. On a regular basis, S&T [and CWMD] meets with other DHS components and interagency partners to gather requirements for risk assessments and to ensure that the results are vetted by the appropriate experts. (DHS, 2021, p. 2)

This is consistent with a well-conducted risk assessment (see Box 2-1).7

Intelligence-Informed Leadership Judgment—or Intel-Driven Assessments

Intelligence assessments follow strict analysis and reporting guidelines (Grabo, 2002; DIA, 2009) to characterize and understand threats to the United States. For long-standing intelligence oversight reasons, the Intelligence Community (IC) does not collect information on or analyze interactions with U.S. plans and choices, nor does the IC typically assess the consequences or vulnerabilities to the United States or its interests. However, those developing strategy may use intelligence reports to develop their own “intel-driven assessments” or “intelligence-informed leadership judgment” (Roberts, 2022).

___________________

7 The committee had no opportunity to validate this claim.

Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 8
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 9
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 10
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 11
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 12
Suggested Citation:"2 Risk Analysis." National Academies of Sciences, Engineering, and Medicine. 2023. Risk Analysis Methods for Nuclear War and Nuclear Terrorism: Phase II (Abbreviated Report of the CUI Version). Washington, DC: The National Academies Press. doi: 10.17226/27393.
×
Page 13
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The Committee on Risk Analysis Methods for Nuclear War and Nuclear Terrorism was established and managed by the National Academies of Sciences, Medicine, and Engineering in response to a congressional mandate to independently explore U.S. government methods for assessing nuclear war and nuclear terrorism risks and how those assessments are used to develop strategy and policy. This publication is the public, abbreviated version of the classified report.

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