In this evaluation of U.S. climate modeling efforts, the Climate Research Committee (CRC) was asked by USGCRP agency program managers to address three key questions, which form the basis for the NRC Statement of Task (Appendix B) for this report:

1. Do USGCRP agencies have a coordinated approach for prioritizing from a national perspective their climate modeling research and assessment efforts?

2. Are resources allocated effectively to address such priorities? A related question that the report addresses is whether currently available resources in the United States are adequate for the purpose of high-end climate modeling.

3. How can the U.S. climate modeling community make more efficient use of its available resources?

• Regarding the first question — the CRC has reached the conclusion that although individual federal agencies may have established well-defined priorities for climate modeling research, there is no integrated national strategy designed to encourage climate modeling that specifically addresses, for example, the objectives of the USGCRP, the needs for comprehensive contributions to the IPCC science base, and the priorities developed by the CRC in its chapter in the Board on Atmospheric Sciences and Climate's report, Atmospheric Sciences Entering the Twenty-First Century (NRC, 1998a). We suggest that the science-driven climate modeling agenda, which has been largely shaped by individual investigators, has been reasonably effective in advancing the frontiers of science, but has not been adequately responsive to the immediate needs of the broader community (e.g., the “impacts” and “policy” communities).

• With respect to the second question — we find that compared with intermediate and smaller modeling efforts, insufficient human and computational resources are being devoted to high-end, computer intensive, comprehensive modeling, perhaps, in part, because of the absence of a nationally-coordinated modeling strategy. Consequently, in contrast to some of the foreign modeling centers, U.S. modeling centers have found it difficult to perform coupled atmosphere–ocean climate change scenario simulations at the spatial resolutions relevant to certain national policy decisions (e.g., finer than 500 km × 800 km). The recognized strengths of U.S. intermediate modeling capabilities (see, e.g., the sizable contributions from the U.S. coarse-resolution climate modeling efforts in the IPCC reports) have not been effectively harnessed in the development of high-end, U.S.-based models. For instance, leading Earth system modeling efforts in the United States suffer from a computationally limited ability to test and run models in a timely fashion. The ability of the climate community to acquire state-of-the-art mainframes is severely ham-