1. documentation of global change;

  2. studies of earlier global change using paleo proxies;

  3. predictions of global change including regional implications;

  4. “focused research initiatives to understand the nature of and interactions among physical, chemical, biological, and social processes related to global change.”

It also called upon the National Research Council to evaluate the science plan and provide priorities of future global change research. This was the motivation behind the NRC “Pathways” report (NRC, 1999a).

The Pathways report pointed out the flaws in the conception and implementation of the USGCRP—in particular that “in practice, the monitoring of climate variability is not currently an operational requirement of the USGCRP nor is there an agency of the U.S. government that accepts climate monitoring as an operational requirement or is committed to it as a goal.” It also expanded the domain of climate research to include variability on seasonal-to-interannual and decadal-to-centennial time scales.

A group of agencies, each devoted only to research and combined in the USGCRP, is currently the only institutional arrangement for performing climate research; for establishing and sustaining a climate observing system; for identifying, developing and producing climate information products; for delivery of these products; and for building the general infrastructure needed to accomplish these tasks. The USGCRP is currently the only entity organized to develop climate models and to secure the computational and human infrastructure needed to respond to the demands placed on the climate modeling community. About 6% of the $1.8 billion annually allocated to the USGCRP is devoted to modeling and this includes the major data assimilation efforts of the NASA Data Assimilation Office.


With a sustained computer capability of 20 Gflops, the current capability of some of the U.S. high-end centers, a climate model consisting of a 300 km resolution atmosphere with 20 levels in the vertical, a land model, and 100 km ocean model, all coupled together and well coded for parallel machines is able to simulate 5–10 years per wall-clock day (see http://www.cgd.ucar.edu/pcm/sc99/img002.jpg . A 1000-year run would therefore take between 3 and 6 months to complete as a dedicated job. As we will see in the next section, these run times are too long to address some of the recent demands placed on the U.S. climate modeling community.

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