anticipated as the hardware concurrency in machines grows. Investments that emphasize system software and workflow reliability and investments in achieving faster execution rates both need to be balanced.

Adoption of these approaches will involve extraordinary levels of effort by the climate modeling community, who will probably have a minimal influence on the hardware or the software roadmap. Various studies on exascale computing have noted that the computational profile of climate science is unique because of the tightly coupled multiphysics nature of the codes.

SOFTWARE INFRASTRUCTURE FOR MANAGING MODEL HIERARCHIES

The community is best served by adopting a domain-specific technical infrastructure under which its developments can proceed. At the scale of one lab, this has been widely adopted and extremely successful. For example, at most modeling centers, scientists do not directly apply MPI or learn the intricacies of tuning parallel file-system performance, but use a lab-wide common modeling infrastructure for dealing with parallelism, I/O, diagnostics, model coupling, and so on, and for modeling workflow (the process of configuring, running, and analysis of model results). Many things that are done routinely—adding a new model component, adapting to new hardware—could not be done without a growing reliance on shared infrastructure.

It was recognized over a decade ago that such software infrastructure could usefully be developed and shared across the climate modeling community. The most ambitious such project was the Earth System Modeling Framework (ESMF; Hill et al., 2004). It introduced the notion of superstructure, a scaffolding allowing model components to be coupled together following certain rules and conventions to permit easy interchange of components between models (Dickinson et al., 2002). See Box 10.2 for a further description of ESMF and how it has unfolded after a decade of development. ESMF and other examples of common infrastructures, including the Flexible Modeling System (FMS)5 developed by the Geophysical Fluid Dynamics Laboratory (GFDL), the Model Coupling Toolkit, extensively used in the CESM, and OASIS, a European model coupling project, are the subject of a comparative survey by Valcke et al. (2012).

This committee, which includes several members closely involved in the development of ESMF and other single-institution frameworks, observes that the idea of frameworks and component-based design is no longer novel or controversial. While switching

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5http://www.gfdl.noaa.gov/fms (accessed October 11, 2012).



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