ily reduce projection uncertainty about some aspects of climate change. Indeed, global climate sensitivity, defined as the global warming simulated by a climate model in response to a sustained doubling of atmospheric CO2 concentrations, still shows a similar 30 percent spread3 across leading models as it did 20 years ago.

Climate Information Delivery to Users

Although a number of aspects of the climate system can be projected with some degree of confidence, this climate information may not be useful for making decisions. As climate models have become more ambitious, so have their users. Many users of climate model outputs need to make decisions on how or whether to respond to climate change, in some cases within institutions where the reality or importance of climate change is not universally acknowledged. Users consider the information from the climate models a valuable commodity, but they are not always sure what data are available to them or how to best use them to inform their decisions. The research community, both by limited capacity and by culture, is often hard pressed to respond to the desires of the user community for new types of model output at high time and space resolution. Quantifying uncertainty in climate projections is still a multifaceted research problem, making communication of relevant uncertainties with diverse user groups challenging, especially when these uncertainties are perceived to be discouragingly large or the climate model output is only part of a modeling chain.

WHY THIS STUDY?

With many studies and reports showing that there will likely be significant impacts as a result of climate change (IPCC, 2007a,b,c; NRC, 2010a,b,d,e, 2011a), now is an appropriate time to examine the capabilities of the nation’s climate modeling enterprise to ensure that it is advancing adequately. The modeling community has already developed plans to make continued progress over the next 3-5 years. However, both the climate science and applications communities would enormously benefit from a major advance in improving the usefulness of climate projections, especially on regional space scales and decadal time scales and including trends in extreme events. Is this possible? Is this likely? How can the United States best position itself to advance and better use climate models? What resources and planning will that take? The need has arisen for a forward-looking, comprehensive, strategic assessment of how best to improve the United States’ capabilities to simulate past, present, and future climate on local to global scales and at decadal to centennial time scales.

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3 This is a 30 percent interquartile spread; see previous footnote for definition of interquartile.



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