8

Conclusions and Next Steps

This report explores the nature and the use of risk analysis methods to assess the risks of nuclear war and nuclear terrorism, based on unclassified information. In doing so, the report explores the structure of risk analysis, the history and literature of risk assessment for nuclear war and nuclear terrorism, and approaches to understanding the threat of nuclear war and nuclear terrorism.

This is the first in a two-part effort; the second phase will expand the focus to include an analysis of the role that the methods and assumptions in risk analysis may play in U.S. security strategy. This second phase is expected to produce a classified report, along with an unclassified summary.

New technologies, including in cyber and space domains, offer technical means to reduce the risks of—but also to provide new routes toward—crisis and conflict. Whether the overall risks are increasing or decreasing with time is unclear, but the uncertainties in the risks associated with nuclear conflict have been increasing over recent decades because of the emergence and broad dissemination of powerful new technologies, as well as a shift toward multipolar nuclear competition.

The committee reached 11 conclusions, as detailed in the preceding chapters.

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 risk of nuclear terrorism have likewise evolved over time, taking into account the new threats and emerging technologies.

CONCLUSION 4-1: There is a need to improve the understanding of less-well-understood physical effects of nuclear weapons (such as 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.

CONCLUSION 4-2: The U.S. government and the international community have invested significant resources and time in trying to understand and reduce the risks of nuclear war and nuclear terrorism. The risks remain real and are becoming more complex as new technologies and new adversaries arise.

CONCLUSION 4-3: There is a fundamental lack of direct evidence about nuclear war and nuclear terrorism. Analysts attempt to mitigate the resulting uncertainties by applying different methods and using multiple sources of information to supplement the limited body of evidence.

CONCLUSION 4-4: Assessing the overall risks of nuclear war and nuclear terrorism involves great uncertainties about the likelihood and consequences of different scenarios. The assessment and communications of these uncertainties are critical for policy decisions essential to managing these risks.

CONCLUSION 4-5: The value of risk analysis is not solely in assessing the overall risks of nuclear war or nuclear terrorism. Risk analysis can provide valuable input on many specific problems related to nuclear war and nuclear terrorism, including an understanding of the uncertainties involved.

CONCLUSION 5-1: Information elicited from experts is often all that is available for assessing some aspects of the risks associated with nuclear war and nuclear terrorism. Analysts and decision makers need to be aware of the sources of that information, of the biases and limitations that the experts could introduce in the analysis, and of the resulting effects of this information on the results of risk analyses. Best practices for expert elicitation can be adapted from other risk analysis disciplines, although some aspects of nuclear war and nuclear terrorism may pose challenges in applying these methods.

CONCLUSION 5-2: Analysts inevitably make assumptions in risk analysis, including about the definition and framing of the risk problem; which models can be used effectively; the reliability of the available data; and the capabilities, intent, and potential actions of adversaries. It is important to show and clearly communicate assumptions and related uncertainties in a risk analysis and their effect on the results.

CONCLUSION 5-3: Strategic assumptions can affect the characterization of a risk problem. Some strategic assumptions address the nature or magnitude of risks, the effect of risk drivers, whether policies or actions increase or decrease the risks, the nature and the variety of threats that confront the United States, and the most likely scenarios. Strategic assumptions also concern risks of nuclear wars outside the borders of the United States.

CONCLUSION 6-1: Different methods of risk assessment are more or less well suited for different situations and goals. For risk management problems that involve significant uncertainties and a need to make resource-constrained decisions, assessing the risk variations associated with different options can help inform decision making. The results of relative risk assessments may be more useful and easier to communicate to a decision maker than the absolute risks.

CONCLUSION 7-1: The ways that risk information is assessed, framed, or presented have powerful effects on how that information is understood and used in decisions. Risk analysis results are most valuable when the method and assumptions by which they were generated is clear, the process is replicable, trust in the analytical process is established, and the analysis addresses the real questions or decisions that confront the decision makers.

On the basis of these specific conclusions, the committee offers three overall conclusions.

1. Past examples of nuclear war and nuclear terrorism are rare. As such, there is little direct evidence that can be relied on to make empirical estimates about the probability of either.
2. The scenarios that might lead to nuclear war and nuclear terrorism are numerous and involve many interdependent factors, and the assessment of their risks often depend on the capabilities, values, perceptions, and intentions of many experts and actors.
3. Different risk assessment methods are more or less suited to different situations and goals.