artificial, so some redundancy in material presented is inevitable. However, the committee suggests that Chapter 2 focus on the various observing systems and Chapter 4 focus on trends in the observations, as differentiated in the following:

Chapter 2 should focus on:

  1. explaining the measuring systems and instrumentation, their accuracy and precision, and spatial temporal variability for global measurements of temperature;

  2. addressing measurement issues both for surface temperature measurements and atmospheric temperature measurements;

  3. addressing spatial and temporal sampling errors; and

  4. discussing any particular geographic regions where measurement and retrieval errors are particularly large.

Chapter 4 should focus on:

  1. errors associated with trends; and

  2. assessing which of the bias errors in Chapter 2 could influence the trends, and why they do or do not do so.

The discussion related to trend estimation and uncertainties in Chapter 2 should be moved to Chapter 4. Text on reanalysis trends from lines 266-277 should be moved to Section 7 (“Reanalysis”) in Chapter 4. Also, Chapter 4 should add a section on “Methodological uncertainties” by including from Chapter 2 most of the text about linear trends in Section 2b (lines 385-460), discussions on structural uncertainty from lines 480-521, and the summary on “Errors or differences related to analysis or interpretation” from lines 584-601.

Alternatively, all material on trend estimation and uncertainties may be brought together in an appendix to the Temperature Trends report. In addition to the above material, discussion of statistical uncertainty in Chapter 3 (pages 39-40) could be included in the appendix.

2. Quantitative information is needed about the strengths and limitations of the observing systems. Specifically, quantitative discussion of the following sources of uncertainties should be included: accuracy and precision of the sensor, uncertainties in converting the fundamental measurement into temperature, and spatial and temporal sampling errors. There should be a summary of studies (with references) in which the different measurement types (e.g., radiosondes, active sensors, different satellite retrievals) have been intercompared and evaluated on a pixel level.

3. Increased discussion is needed on surface temperature measurements and trends, to parallel the detailed discussion provided on atmospheric temperatures. From reading this document, the impression is given that global surface temperature measurement is a solved problem, but this is not the case. Description of skin and bulk sea surface temperature (SST) in Chapter 4.5.1 should be moved to Chapter 2 and should reference the recent work of Chelton (2005). Errors associated with sea surface temperature measurement are not adequately covered in either Chapters 2 or 4. Discussion of microwave SST and blended infrared/microwave products should be included. Note, the

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