Computer simulation models are the primary tools by which knowledge of the workings of the Earth System can be integrated, and the results of these models are, in many ways, one of the major payoffs of the USGCRP. Only through Earth system models can we, for example, predict future climate variability and change, including the possible effects of human activities on the global climate system. The long-term objective of Earth system modeling and simulation is to create and apply models that provide credible predictions (including levels of certainty and uncertainty) of changes and variations in climate on regional-to-global scales, along with useful projections of potential environmental and societal consequences. Gaining scientific understanding and predictive capability for variability and change in our planet’s environment requires the study of the dynamic interactions among the major components of the Earth system, including the oceans, atmosphere, land surface, and sea ice.
Over the past several years, a number of internal and external analyses have identified significant problems with the U.S. climate modeling effort. The most recent of these is a study by the National Research Council, Capability of U.S. Climate Modeling to Support Climate Change Assessment Activities, which states that while the U.S. community is "a world leader in intermediate and smaller climate modeling efforts, it has been less prominent in producing high-end climate modeling results, which have been featured in recent international assessments of the impact of climate change." In the modeling community, the U.S. has been falling behind many other nations in its ability to perform long-term climate simulations. Modeling centers in Australia, Canada, England, Germany, and elsewhere have computational abilities that far exceed those of U.S. centers. The U.S. is now relying heavily on these foreign modeling centers in producing scenarios of how climate will evolve in the future. The NRC report went on to state that
. . .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. . .In order to optimally use existing scientific capabilities, adequate resources, including greatly improved supercomputing capabilities, need to be provided to the climate modeling community. The reliance of the United States upon other countries for high-end climate modeling must be redressed.
Figure 9. Ocean circulation: comparison of modeling and observation
The USGCRP agencies are working to provide short-term relief to the current computing capacity shortfall in the Nation’s leading climate modeling centers. However, incremental changes to current capability and program structure will not be adequate to the long-term task. A more substantial response to this need is underway.
With DOE and NSF taking the lead, the USGCRP has been developing a long-range, Accelerated Climate Prediction Initiative (ACPI). The ACPI takes an integrated view of the improvements required to accelerate progress in climate simulation and projection of climate change. Interrelated activities in model development and evaluation, simulations, and projections, and analysis and assessment will be addressed by concurrent improvements in the models themselves, data availability and usefulness, computer speed and memory, collaboration and data management capabilities, and widespread institutional interaction. The USGCRP agencies will develop a more integrated modeling strategy, including improved program integration and development of overall USGCRP climate modeling priorities that are closely linked to overall USGCRP climate system research objectives.
Major steps forward in large-scale U.S. climate modeling will require major increases in computational resources and a coupling of increased computational capability with increased scientific knowledge of climatological phenomena. Indeed, the specifically articulated goals of the ACPI are to: (1) accelerate progress in general circulation model development and application; (2) reduce substantially the uncertainties in model-based projections of global environmental change on the full range of relevant timescales; and (3) increase the availability and usability of global change projections to the broader environmental research and environmental assessment communities.
It is estimated that these goals will require, from the hardware side, horizontal model resolutions of 30 km in the atmosphere, 1 km of the land surface, and 5-10 km in the ocean. These needs, added to the requirements of multiple ensemble runs for statistical confidence, dictate the imperative for teraflop (trillions of operations per second) computational capability.
To achieve this enhancement of the Nation’s climate modeling capabilities,
many of the USGCRP agencies are participating in the Administration’s Information
Technology for the 21st Century initiative. The information technology
focus for the USGCRP is on developing computational tools that will support
climate modeling using the teraflop-scale computational resources created
and made available through the overall Information Technology Initiative.
This will be a key aspect of implementing the integrated strategy that
is being developed through the ACPI.