While current reanalysis products provide a foundation for climate research, reanalysis data are now used in an increasing range of commercial and business applications, such as energy (supply/demand analysis, assessing locations for wind power generation), agriculture, water resource management, insurance and reinsurance. Thus the Climate Change Science Program’s (CCSP) Synthesis and Assessment Product (SAP) 1.3 will potentially be very beneficial to all stakeholders of climate change science. The committee commends CCSP and the National Oceanic and Atmospheric Administration (NOAA) for emphasizing the need to address this important topic.

This chapter outlines the major issues that, from the point of view of the review committee, the authors should strongly consider addressing in the revised version of SAP 1.3. In some cases, findings are simply noted without explicit recommendations. In other cases, the committee provides either a direct recommendation or alternatives for the authors to consider as they address the review findings. In subsequent chapters of this report, the committee provides further overarching thoughts on the draft document and findings and recommendations specific to individual chapters of the draft. Comments regarding key issues follow.

The committee finds that in general, the authors nicely summarize the capability of current reanalysis for quantifying climate variations and long-term trends. SAP 1.3 appears to be scientifically objective and policy neutral. In cases where the results of SAP 1.3 are compared with existing peer-reviewed literature, the SAP 1.3 results are consistent with existing data. However, a significant fraction of the SAP 1.3 results is not compared with peer-reviewed literature and the authors are encouraged to compare their results with the peer-reviewed literature whenever possible. The authors correctly point out that the strength of current atmospheric reanalysis is its global coverage and complete description of atmospheric states, and that the reanalysis is best used for quantifying atmospheric processes at synoptic to decadal time scales (including describing the El Niño-Southern Oscillation (ENSO) and the spatial patterns of atmospheric modes such as the Pacific-North America Oscillation (PNA), the North Atlantic Oscillation (NAO)) , but not appropriate for longer-term changes (for example trends in precipitation, atmospheric water vapor or even surface air temperature). The authors rightly state that substantial efforts are needed to correct biases and discontinuities in various observational data before they are assimilated into reanalysis. The committee commends the authors for clearly stating their goals and their intended audience and for their fidelity in following the prospectus.

The primary issues identified by the committee focus on the effectiveness of the document’s presentation, level of technicality and organization, as well as accessibility of the document to its target audiences. The committee identified the following issues and offers suggestions on how to improve the document.

  1. The title and contents of the document are not entirely consistent. The title of the present draft, “Reanalyses of Historical Climate Data for Key Atmospheric Features: Implications for Attribution of Causes of Observed Change,” correctly suggests that reanalysis data is useful for attributing the causes of observed climate change. This link, however, is often missing and attribution is not tied to reanalysis directly. All

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