vanced), if not by reduced modeling uncertainty. Uncertainty in projection of regional precipitation trends will also remain substantial; we envision gradual progress over the next decade or two as the diverse sources of this uncertainty are all incrementally reduced through model improvements and a longer, higher-quality observational record. A 50 percent reduction in model-related uncertainty in climate sensitivity or precipitation response to a given greenhouse gas change over the next 10-20 years would be an optimistic hope.

Climate is complex, multiscale, and multifaceted. Even with the strategic plan we envision, overall improvements in climate models will likely be gradual, not revolutionary. Nevertheless, they can have huge economic value to the nation, because climate change affects everyone and should be a factor in a myriad of planning decisions around the country.

FINAL COMMENTS

Climate models are among the most sophisticated simulation tools developed by mankind, and the “what-if” questions we are asking of them involve a mind-boggling number of connected systems. As the scope of climate models has expanded, so has the need to validate and improve them. Enormous progress has been made in the past several decades in improving the utility and robustness of climate models, but more is needed to meet the growing needs of decision makers who are increasingly relying on the information from climate models.

The committee believes that the best path forward is a strategy centered around the integration of the decentralized U.S. climate modeling enterprise—across modeling efforts, across a hierarchy of model types, across modeling communities focused on different space and time scales, and between model developers and model output users. A diversity of approaches is necessary for progress in many areas of climate modeling and vital for addressing the breadth of users needs. If adopted, this strategy of increased unification amidst diversity will allow the United States to more effectively and efficiently utilize that diversity to meet the climate information needs of the nation in the coming decades and beyond.



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