Thursday, January 3, 2013

National Strategy for Advancing Climate Modeling

NAP has a new report out on a national strategy for advancing climate modeling. I've just done a quick skim so far. Some tidbits below that touch on V&V and uncertainty.

  • The possibility of irreproducible computation presents a challenge to testing, verification, and validation of model results. Chaotic systems with sensitive dependence on initial conditions will wander arbitrarily far outside any tolerance bound, given enough time. The key question in the climate context is to see whether trajectories subject to small changes at the hardware bit level stay within the same basin of attraction, or do these small errors actually push the system into a “different climate state.”
  • For decadal and longer time scales, the problem of quantifying prediction skill becomes even more difficult, and the metrics will likely involve how the forecasts are used in applications.
  • Effective communication about climate change and its uncertainty to science managers and decision makers is a crucial part of advancing our national climate modeling capability. There is no simple formulaic way to communicate uncertainty; as climate models and their available outputs become more sophisticated, those looking to use this information struggle to keep up.
  • As these challenges are faced and models grow in complexity, they are likely to exhibit an increasingly rich range of behavior, full of surprises and unexpected results. Therefore, the committee emphasizes that it is unwise to promise that successive generations of models will invariably result in firmer predictive capability. [Tennekes predicted this]
  • In order to use climate model projections to inform its decisions, the Navy would need high-spatial-resolution regional climate models on decadal time scales, uncertainty quantification of the models, and probability distribution functions in the model output. The Navy is a “good example of a stakeholder that has very specific needs in applications related to its infrastructure and operations, disease, civil instability, migration, water resources, and energy” (NRC, 2011c)

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