benefits associated with an issue based on the trust it has in the institution or process (Earle and Cvetkovich 1995; Siegrist et al. 2000).

Trust in an assessment, as in any process that relies on deliberation among multiple individuals, requires that the process be seen as both fair and competent (i.e., legitimate and credible) (Habermas 1970; Renn et al. 1995). Because trust conflates fairness and competence (Habermas 1970), the terms “credibility” and “legitimacy” are used instead throughout this report to distinguish the two sources of trust (Ravetz 1971; Clark and Majone 1985; Social Learning Group 2001a). Legitimacy implies that those who have a view on the issue, and those who will be affected by decisions that emerge from the process, have the opportunity to have a say in the process either directly or through a third party whom they trust. Further, it requires that the process allows all views to be given serious consideration, with the outcomes determined by thoughtful deliberation under rules seen as acceptable to all participants. Credibility implies that those who have knowledge relevant to the issues at hand participate in ways that allow their knowledge to influence the discussion, either through their direct participation or through consideration of their work.

The following questions provide guidance for global change assessments to achieve credibility and legitimacy:

  • Who has interests at stake in the outcomes of the assessment process?

  • What kind of expertise is required to understand the issues being considered?

Process assessments, impact assessments, and response assessments differ considerably in who has interests at stake, what kinds of expertise are relevant, and who has that expertise. Thus, implementation of the requirements for a legitimate and credible assessment will differ across the three types of assessments.

Process Assessments

Process assessments describe the state of the natural world as we understand it, the global change of interest, and its natural and anthropogenic causes (for detailed definition see Chapter 2). They are not intended to provide policy options, and therefore strive to avoid analysis of values, such as benefits, costs, or risk preferences. This simplifies the task of achieving credibility and legitimacy compared to impact assessments that inevitably consider value judgments and trade-offs. Science has strong norms for how to carry out deliberations about the state of knowledge, so it is relatively easy, in principle if not in practice, to conduct a credible process assessment

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