global surface air temperature than is climate model uncertainty (IPCC, 2007c, Figure 10.29). Morgan et al. (2009) has noted that “in some cases, all the research in the world may not eliminate key uncertainties on the timescale of decisions we must make.”

Finding 6.2: The climate science community has made considerable progress in quantifying uncertainty in climate simulations, but progress in reducing certain types of uncertainty has been slow, and further reduction may not be possible for certain aspects of long-term projections.


Communicating uncertainty is a relevant topic for advancing climate modeling because it relates to decision making (see next section) for adaptation, mitigation, and regarding what aspects of a model may be most important to improve. The appropriate approach to communication depends on the particular audience and on the purpose of the communication. Moreover, the appropriate approach to communication partially depends on the purpose of the communication. Is it for general education, making people aware of important issues, or is it to inspire specific actions regarding managing climate resources, or is it for the sake of shaping the needs for future climate model development? Communications of scientists to scientists about uncertainty are very different from their communication with the lay public.

Review of Communication Approaches

There has been a steady increase in the attention that communicating about climate and climate change has received, and this communication has been carefully considered within the community of scientists. For example, in IPCC (2007c) there were descriptions of scientific understanding and likelihood of specific results. A standard language was developed with narrative terms; for example, “likely” was linked to quantitative statistics, >66 percent probability. An entire Synthesis and Assessment Report (SAP) of the Climate Change Science Program (CCSP, 2009) was dedicated to establishing best practice approaches of characterizing and communicating uncertainty (Morgan et al., 2009). In Advancing the Science of Climate Change (NRC, 2010b), considerable effort is devoted to describing the terminology of uncertainty, the nature of uncertainty in the culture of science, and the use of uncertainty in decision making. This section emphasizes and discusses some issues associated with the communication of uncertainty that have evolved or emerged since these earlier works and that are relevant to climate modeling.

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