World Meteorological Orginization Assessments). The key points should be based on the detailed discussions within each chapter. The chapters should in some cases include more scientific rigor (as detailed in the chapter reviews that follow) and be aimed at the broad climate science community. One possible strategy for including scientific rigor in the chapters is to use footnotes to describe technical details, as was done in Chapter 5.

3. More explicit discussion of the statistical characterization of uncertainty in trends is needed, with emphasis on several specific topics.

a. The conclusions reached in the report are often based on estimates of trends, neglecting uncertainty levels, and many statements on comparisons are inaccurate because of this. Uncertainties are relatively large because of small trend signals, large natural variability, and data records that are relatively short. Conclusions within the report should more accurately reflect the uncertainties inherent in the statistical trend calculations.

b. A more thorough discussion of the detailed statistical trend calculations for the various data sets is needed. This discussion might be appropriately placed within an appendix.

c. When comparing trend differences between two estimates of the same quantity (e.g., tropospheric temperatures from radiosondes and satellites), it is more appropriate to examine the trend of the difference time series, rather than trends for each time series individually (because the data contain similar overall variability). Specific instances where this is relevant are identified in the chapter reviews that follow.

4. The report would benefit from a more critical evaluation of the trend differences between the University of Alabama, Huntsville (UAH) and Remote Sensing Systems (RSS) satellite microwave data sets. The report presents results from UAH, RSS, and University of Maryland (UMD) satellite data and effectively treats the UAH and RSS results as equal independent estimates with a lesser discussion of UMD results because the latter do not include a diurnal correction and because their newest analysis appeared only recently. An expanded discussion and critical assessment of the UAH and RSS differences is needed in particular, as well as a discussion of the implication of the differences. The committee would like to see a resolution of this difference or, if that is not possible within the current report, some discussion of what sorts of analyses would be required to resolve the differences between the two groups’ trend estimates. Similar scrutiny of the UMD product and its associated uncertainties would be valuable.

5. Satellite trends derived from combining separate microwave channels (the so-called Fu et al. technique, as described in Fu and Johanson [2004 and 2005], and Fu et al. [2004a and b]) should be discussed in more detail. The Fu et al. results are potentially of key importance to the issue of tropospheric temperature trends and should be discussed more thoroughly. Currently, there is minimal discussion, and the data are labeled “controversial”. A more thoughtful and balanced appraisal is necessary, and more recent references should be included.

6. A more thorough discussion of biases in trends derived from historical radiosonde data is needed. The report concludes that stratospheric trends derived from radiosondes are biased so badly as to be unbelievable (a result for which there appears to be a



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