presented in Chapter 3. Reliance on a single metric can provide an erroneous sense of progress and increase the potential for misuse (principle 8). The principle that metrics should address both process and progress (principle 7) is particularly relevant for complex and diverse programs such as the CCSP. Importantly, the meaning of uncertainty is poorly defined for much of the scope of the CCSP. It is likely that different definitions apply to different program elements (e.g., overarching goal, prioritization criteria, research question, milestone). Without careful definition, reducing uncertainty cannot be evaluated using specific observable or articulated measures. Therefore, it violates the principle that metrics should be easily understood and broadly accepted by the community (principle 5). To be meaningful, a metric must first be based on a well-specified variable that indicates advancement of knowledge. Second, a precise definition of what is meant by “uncertainty” in reference to that variable must be specified. The pervasive and diverse use of reducing uncertainty as a definition of progress, and the flaws and potential misuse of reducing uncertainty as a metric, warrant a more detailed assessment of its application for the CCSP.


The climate community expresses uncertainty in different ways.1 The CCSP defines uncertainty as:

An expression of the degree to which a value (e.g., the future state of the climate system) is unknown. Uncertainty can result from lack of information or from disagreement about what is known or even knowable. It may have many types of sources, from quantifiable errors in the data to ambiguously defined concepts or terminology, or uncertain projections of human behavior.2

Uncertainty plays a key role in policy formation because decisions often turn on the question of whether scientific understanding is sufficient to justify particular types of response. The CCSP strategic plan seeks to develop knowledge of the complex human-natural system in support of public and private decisions, and a central component of this task concerns character-


For example, see Lempert, R., N. Nakicenovic, D. Sarewitz, and M. Schlesinger, 2004, Characterizing climate-change uncertainties for decision-makers, Climatic Change, 65, 1–9; Intergovernmental Panel on Climate Change, 2004, Describing Scientific Uncertainties in Climate Change to Support Analysis of Risk and of Options: Workshop Report, M. Manning, M. Petit, D. Easterling, J. Murphy, A. Partwardhan, H.-H. Rogner, R. Swart, and G. Yohe, eds., Report of a workshop held at the National University of Ireland, Maynooth, May 11–13, 2004, 138 pp., <>.


Climate Change Science Program and Subcommittee on Global Change Research, 2003, Strategic Plan for the U.S. Climate Change Science Program, Washington, D.C., p. 199.

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