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The National Academies of Sciences, Engineering and Medicine
Board on Environmental Change and Society
Board on Environmental Change and Society
Division of Behavioral and Social Sciences and Education
Methods for Characterizing Risk in Climate Change Assessments: A Workshop

March 23-24, 2016

Archived Workshop Materials

Read two recent articles commenting on the discussions at the workshop

Scientists' struggle: talking climate 'in plain English' — Climate Wire (March 28, 2016)
Climate: Top Scientists find it hard to make public see risks — Greenwire (March 25, 2016)
Project Scope

An ad hoc steering committee will organize a public workshop designed to inform the approaches to characterizing and communicating risk within the National Climate Assessment (NCA). The steering committee will identify a series of case examples to use to explore issues such as the following, in the context of the NCA report:
  • Methods, procedures, and terminology for characterizing risks;
  • Strategies for conveying information about risks;
  • Ways to enhance the ability to compare risk information across different regions and sectors; and
  • Research needs and near-term actions required to support and improve risk characterization and communication in future national assessments.

Sponsor: U.S. Global Change Research Program


Joseph Arvai, Chair, University of Michigan
Kristie Ebi, University of Washington
Baruch Fischhoff, Carnegie Mellon University
Peter Gleick, Pacific Institute for Studies in Development, Environment, and Security
Andrew Hoffman, University of Michigan
Richard Moss, University of Maryland, College Park
Claudia Tebaldi, National Center for Atmospheric Research
Chris Weaver, U.S. Environmental Protection Agency
Robyn Wilson, Ohio State University

Mary Ellen O'Connell, Interim Director
Paul Stern, Study Director
Mary Ghitelman, Program Assistant


The U.S. Global Change Research Program was established in 1990 to “assist the Nation and the world to understand, assess, predict, and respond to human-induced and natural processes of global change.” In response to this legislative mandate, the Program conducts periodic National Climate Assessments (NCAs) to inform the nation about observed changes in climate, the current status of the climate, and anticipated trends for the future. These assessments seek to anticipate the consequences of climate change for the nation as a whole, as well as for its geographic regions and for affected sectors (e.g., water, energy, transportation). The Program has now conducted national assessments on three occasions, the most recent having been completed in 2014. The Program intends to develop a sustained assessment process, using the past assessments as a starting point.

A key to making assessments of the impacts of climate change useful is to provide information about climate-related hazards, risks, and opportunities in formats that are useful to decision makers in their efforts to reduce greenhouse gas emissions and to reduce vulnerability and increase resilience to climate change in the regions or sectors for which they are responsible. To be credible and useful, such information must be based on systematic, scientifically defensible methods, understandable and decision-relevant from a decision maker's perspective, appropriately attentive to uncertainties, and sufficiently consistent in method over time to allow for assessing whether and to what degree climate-related risks, vulnerabilities, and resilience have changed. Of critical importance is the ability to integrate risks resulting from climate change into analytic and decision making processes that evaluate and manage other risks with which decision makers are more familiar (GAO, 2013).

Many approaches are available for analyzing and characterizing hazards and risks (e.g., NRC, 1989, 1996), including climate-related risks. Some of these produce monetary estimates of risks such as are used in the insurance industry; some estimate the likelihoods of particular hazardous events occurring in a particular place and time frame (e.g., 100-year flood maps); some provide numerical or qualitative ratings of risks; some project vulnerability or assess readiness; and some use other approaches. Each method has potential advantages and limitations, and several of them have established histories with particular groups of decision managers. The methods also differ in the extent to which they are developed by consultation between risk analysts and the potential users of risk information.

The need for national, sustained assessments of climate change creates new challenges for characterizing risks because climate change presents so many different kinds of hazards, different kinds of entities exposed to risk, different kinds of decision makers, and different time frames during which risks may be experienced. It may be tempting to characterize risks for all decision purposes using standard language, such as the language of formal risk analysis, but efforts to do this have often been unsatisfactory to decision makers.

Using the variety of approaches that have been developed in different decision domains, however, leads to a cacophony when analysts and decision makers from different domains need to communicate in the context of the NCA, which sometimes requires comparisons of risks across sectors, regions, or populations and consideration of changes in vulnerability and resilience over time. The NCA needs to develop ways of characterizing risks that are useful and mutually intelligible across analyses focused on particular resource types (e.g., water, agriculture, energy, transportation) and specific regions of the USA, as well as for making choices that may affect multiple resource types, kinds of hazards, and exposed populations and property. Using standard metrics facilitates setting priorities, making tradeoffs, and evaluating progress in reducing risks, but there may be good scientific reasons why no single metric has dominated assessment of all the risks presented by climate change. The NCA also needs to take practical steps to facilitate risk characterization, for example improving guidance to authors across closely related topics that were considered separately in NCA3: risk framing, uncertainty, and scenarios. The workshop would use a series of case examples to explore issues related to risk characterization and be designed to inform the sponsor's approach to characterizing risk in the context of the NCA report.

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