The first four steps were done in an iterative consensus process in which a strawman list was vetted and modified by outside experts in several rounds of discussion at committee meetings and workshops. Although such methods have well-known shortcomings (e.g., validity, reliability, problems concerning the consensus among the experts), they have proven useful when it is not possible to obtain objective data (Finkel and Golding, 1994; Davies, 1996). The last step was carried out by the committee, which is responsible for the priorities presented in this report.

The overarching goals of the Climate Change Science Program (CCSP; Appendix B) provided the context for identifying both science and applications priority areas (Step 1; Table C.1). Strawman priority areas (Step 2) were gleaned from workshops and more than 100 published reports and articles to give them a level of community review and acceptance. Among the most important sources were the gaps and weaknesses identified in Evaluating Progress of the U.S. Climate Change Science Program: Methods and Preliminary Results (NRC, 2007) and discussion papers prepared by the National Academies Committee on the Human Dimensions of Global Change (CHDGC) and Climate Research Committee (CRC; see Appendixes D and E). The CHDGC and CRC narrowed down dozens of candidate priorities using criteria similar to those developed by the committee for Step 3 and feedback from the committee.