Summary

A primary objective of the Climate Change Science Program (CCSP) is to provide the best possible scientific information to support public discussion and government and private sector decision making on key climate-related issues. To help meet this objective, the CCSP is producing a series of synthesis and assessment products that address its highest priority research, observation, and decision-support needs. The National Oceanic and Atmospheric Administration (NOAA) is the lead agency on Synthesis and Assessment Product (SAP) 1.3 “Reanalyses of Historical Climate Data for Key Atmospheric Features: Implications for Attribution of Causes of Observed Change”. The objective of this product is to provide an expert assessment of the capability and limitations of state-of-the-art climate reanalyses to describe past and current climate conditions, and the consequent implications for scientifically interpreting the causes of climate variations and change.


As part of the CCSP process, NOAA has requested an independent review of SAP 1.3 by the National Research Council (NRC). The NRC appointed an ad hoc committee of climate scientists who engage in reanalysis efforts to review the draft SAP 1.3 focusing on the extent to which the draft document meets the requirements set forth in the prospectus. The current draft was clearly written for an audience of researchers involved in assessment efforts. The product assesses the capability of current reanalysis for quantifying climate variations and long-term trends. The authors rightly state that substantial efforts are needed to correct biases and discontinuities in various observational data before they are assimilated into reanalyses. The committee commends the authors for clearly stating their goals and their intended audience and for their fidelity in following the prospectus. However, the current draft needs revision to better link reanalysis and attribution. This connection is often missing and attribution is not tied to reanalysis directly. In addition, the document needs to better explain how reanalysis fits into climate science and include a general description of how climate science is done and how the models, observations, and theories are related to the ultimate goal of reanalysis, especially for the benefit of non-specialists. Also, in the technical sections of the report, more details about the models used and statistical methods employed need to be included (see specific chapter reviews).



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Summary A primary objective of the Climate Change Science Program (CCSP) is to provide the best possible scientific information to support public discussion and government and private sector decision making on key climate-related issues. To help meet this objective, the CCSP is producing a series of synthesis and assessment products that address its highest priority research, observation, and decision-support needs. The National Oceanic and Atmospheric Administration (NOAA) is the lead agency on Synthesis and Assessment Product (SAP) 1.3 “Reanalyses of Historical Climate Data for Key Atmospheric Features: Implications for Attribution of Causes of Observed Change”. The objective of this product is to provide an expert assessment of the capability and limitations of state-of-the-art climate reanalyses to describe past and current climate conditions, and the consequent implications for scientifically interpreting the causes of climate variations and change. As part of the CCSP process, NOAA has requested an independent review of SAP 1.3 by the National Research Council (NRC). The NRC appointed an ad hoc committee of climate scientists who engage in reanalysis efforts to review the draft SAP 1.3 focusing on the extent to which the draft document meets the requirements set forth in the prospectus. The current draft was clearly written for an audience of researchers involved in assessment efforts. The product assesses the capability of current reanalysis for quantifying climate variations and long-term trends. The authors rightly state that substantial efforts are needed to correct biases and discontinuities in various observational data before they are assimilated into reanalyses. The committee commends the authors for clearly stating their goals and their intended audience and for their fidelity in following the prospectus. However, the current draft needs revision to better link reanalysis and attribution. This connection is often missing and attribution is not tied to reanalysis directly. In addition, the document needs to better explain how reanalysis fits into climate science and include a general description of how climate science is done and how the models, observations, and theories are related to the ultimate goal of reanalysis, especially for the benefit of non-specialists. Also, in the technical sections of the report, more details about the models used and statistical methods employed need to be included (see specific chapter reviews). 1

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Although the assessments community should find this document extremely helpful, understanding the present level of scientific confidence and remaining uncertainties in identifying and describing how the climate system has varied over approximately the last half-century is critical and should be explained to all stakeholders of climate change science as outlined in the SAP prospectus. In this sense, the current draft of SAP 1.3 falls short of the requirements set forth in the prospectus. The draft does not address all of the specified audiences, particularly “policymakers, decision-makers, and members of the media and general public with an interest in developing a fundamental understanding of the issue.” Chapters 2 and 3 do not necessarily describe the state-of-the-science, the problems in methodology adopted in the current models, and the most uncertain factors in the current research regarding reanalysis and attribution. Much of the data in the product is original research. The authors should explicitly distinguish the findings from the peer-reviewed literature from those derived from original work. The report should give precedence to peer-reviewed literature whenever possible. 2