The committee reviewed draft Synthesis and Assessment Product 3.3, Weather and Climate Extremes in a Changing Climate, focusing on the extent to which the document meets the requirements set forth in its prospectus and using guidelines developed by the U.S. Climate Change Science Program in conjunction with the National Research Council. The committee finds that the draft provides a good and thorough assessment of the important issues regarding extreme events over North America and how they may change in the context of a changing climate. The document may be improved by considering several recommendations regarding its content and format outlined later in this review.
From an architectural and formatting perspective, the document needs significant improvement. The continuity and cohesion among the chapters could be improved by greater coordination among the chapter authorship teams and a concerted effort to consolidate the material. The Executive Summary should clearly and concisely state the major recommendations, which should be contained and discussed in Chapter 4 and not scattered among the chapters. The Preface should focus on the “big-picture” issues and not contain technical material, as it now does.
In the case of tropical cyclones, the material presented is beyond what is necessary or desirable for an assessment document; this material should be reduced significantly and is too detailed for the target audience. Although the content of the Abstract and Executive Summary is written appropriately for their target audience(s), the alarmist tone of the Abstract is inconsistent with the tempered language used elsewhere in the document and is not entirely consistent with the scientific evidence provided. The discussion of drought and ecological impacts should be strengthened and consistent with related statements in the Abstract and Executive Summary. In many cases, particularly for drought and tropical cyclones, claims of trends are not necessarily supported by the available evidence and the underlying statistical methods to assess those trends are unclear or problematic.
Although the committee recommends significant revisions that are intended to lead to an improved final product, the scope, content and scientific rigor of the current draft provide a solid basis for the final version of Synthesis and Assessment Product 3.3.