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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product on Temperature Trends in the Lower Atmosphere Review of Chapter 6 Chapter 6 asks: what measures can be taken to improve the understanding of observed changes? This chapter purports to respond to issues and shortcomings raised in Chapters 1-5 and develops a list of seven comprehensive recommendations. These recommendations address: (1) the need for improved observing standards that are rigorously implemented, (2) better use of existing data, (3) expanded use of regional and global climate models for assessing the impacts of forcings and feedbacks on temperature trends, (4) continued assessment of tropospheric trends using a full range of statistical techniques and modeling tools, (5) enhanced development of reanalyses, (6) improved metadata, and (7) development of scientific talent. The committee finds that the recommendations in Chapter 6 are insufficiently specific and not clearly prioritized. Furthermore, the seven recommendations seem largely disconnected from the findings in Chapters 1-5, and even from the text in Chapter 6. This chapter needs a substantial rewrite, including re-organization of the text and reformulation of the recommendations. MAJOR COMMENTS 1. Chapter 6 should be reorganized into two parts: a. The first part should take findings from Chapters 1-5 to recommend specific opportunities to improve understanding of vertical temperature trends. These should focus on addressing remaining uncertainties in existing satellite and radiosonde data sets. b. The second part should focus on future measurement opportunities in the context of the specific goals of the report for reconciling observations and understanding of temperature trends. 2. Also in reorganizing Chapter 6, the committee recommends starting with the Global Climate Observing System (GCOS) implementation plan and reinforcing, adding to, or modifying that plan, rather than starting from scratch. It is important that the community speak with a unified voice as much as possible. The authors should also discuss the current efforts to improve the relevant temperature measurements in addition to GCOS, including Global Ocean Data Assimilation Experiment (GODAE),
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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product on Temperature Trends in the Lower Atmosphere SEAFLUX, and Global Energy and Water Cycle Experiment (GEWEX) Radiation Panel efforts to develop technologies for reference radiosondes, and discuss international efforts, not just U.S. efforts. 3. The organization of the chapter is centered around data types, such as “surface”, “tropospheric”, and “reanalyses”. A variety of new issues that do not directly map to the seven recommendations are brought up in these sections (much of which is not relevant or belongs in previous chapters). An alternate organization would be to have seven sections with section headings that are the first sentence of each recommendation. Then the text of each section would tie directly back to a need documented in the earlier chapters, would include discussion of the adequacy of current national and international plans to address this need, and make further specific recommendations for implementation of this recommendation. 4. A substantial amount of new information is introduced for the first time in Chapter 6, including material that should have been introduced in earlier chapters if it is deemed relevant and material that does not directly map to the seven recommendations. The following is specific information that is redundant or should be moved to previous chapters: The material in lines 54-71 should be mentioned in the context of Chapters 1 and 5. Text on snow and sea ice and sampling inadequacies in lines 179-187 should be moved to Chapter 2. For lines 138-177, lines 240-254, and lines 300-317, text on combining surface temperature and dew point temperature is far too wordy, and the main point is lost. This concept should be included in a general recommendation on the need to evaluate and interpret the temperature data in the context of other data sets (e.g., humidity, winds, ocean heat content, etc.) and to understand issues such as the impact of changing land use on temperature trends, as stated in lines 347-355. The text in lines 447-494 about recommending specific improved climate model parameterizations is not directly relevant to the present study, although it is appropriate to state in earlier chapters that inadequate parameterizations in numerical weather prediction models contribute to potential problems in using the reanalyses to determine temperature trends. The text in lines 98-105 should be moved to Chapters 2 and 4 as these points were not adequately made in those chapters. 5. As far as the current recommendations in Chapter 6 still appear after the chapter is revised, here are comments on each of the current recommendations. The seven recommendations in Chapter 6 have been said numerous times before in other reports. Also, given the relative lack of traceability of these recommendations to the previous five chapters, it may be that a significant recommendation was omitted. a. The first recommendation concerns reference measurements. The recommendation should be formulated to account for the adequacy or inadequacy of current national and international plans to address this need. If inadequate recommendations are made in previous documents (e.g., GCOS), then very specific
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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product on Temperature Trends in the Lower Atmosphere recommendations should be made to address the sensor design, sampling, or other needs. b. The second recommendation concerns making better use of existing data. See comments for the first recommendation. This section should focus specifically on reprocessing of radiosonde data, resolving the differences between the different MSU analyses, and use of the TIROS Operational Vertical Sounder (TOVS) data, including some very specific recommendations to address the key issues. It should also discuss detailed intercomparison (at the pixel level) of the different data sets and cross checking with other variables. Better scientific uncertainty analysis of the data sets should be part of this recommendation. Specific recommendations here would add considerable value to this document. c. The third recommendation concerns the use of climate models to interpret the cause of temperature trends. This recommendation needs to be reformulated or perhaps eliminated because it is too broad and inappropriate for the present study. What is recommended here should follow directly from Chapter 5 and any uncertainties or inconsistencies in the analyses that were identified. An alternative recommendation would be to “Improve the scientific understanding of the variations of the vertical temperature structure of the atmosphere”. It should also be clearly emphasized that data is being used to test models and not vice-versa. d. The fourth recommendation concerns statistical trend analysis. A clear case has not been made in the previous chapters (or in Chapter 6) that there is a need for new research in the statistical analysis of trends. Rather, the committee would prefer that the report give explicit discussion to existing methods for dealing with such issues as autoregressive behavior and nonlinearities in trends, as already discussed in review comments on Chapter 2. e. The fifth recommendation concerns climate quality reanalyses. Just as for the third recommendation, this one needs to be reformulated or perhaps eliminated. It is not useful to state such a broad recommendation that has already been made in other contexts. If there are any specific recommendations that would help address the temperature trend problem, then they should be formulated. Possibilities would include careful documentation about what assimilation data is actually assimilated into the model as a function of space and time, data assimilation experiments, etc. f. The sixth recommendation concerns metadata. It seems that this issue is (or easily could be) covered in the first recommendation. It is not clear that accessibility of the data is a major issue. g. The seventh recommendation concerns education. This recommendation is very diffuse and is not motivated by the previous chapters. It is hard to disagree with the statement that education in our field should include a stronger emphasis on the proper use of statistics and error analysis. However, this point could easily be incorporated into the second recommendation. h. An outstanding omission in terms of recommendations is the need for better methods to sense temperature or related variables from satellites, such as using instruments that are self calibrating, sounders with more channels for better vertical resolution, and the use of proxy measures such as refractive index and spectral TOA radiance.
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Review of the U.S. Climate Change Science Program’s Synthesis and Assessment Product on Temperature Trends in the Lower Atmosphere SPECIFIC COMMENTS 1. In lines 79-80, it is the committee’s understanding that the U.S. Climate Reference Network been shelved or at least stalled. 2. Most countries do not know about the GCOS Monitoring Principles, mentioned in lines 87-88. 3. Many of the recommendations in lines 150-160 may be difficult to achieve based on cost considerations. The GCOS aim is to get the data first, then work on metadata. Getting pictures of sites will only be useful if they are taken at regular intervals. 4. In lines 198-199, there is a GCOS working group of the Ocean Observing Panel for Climate (OOPC) and the Atmospheric Observing Panel for Climate (AOPC) looking at Sea Surface Temperature biases. 5. In line 287, locating the reference sonde stations for comparison with satellite overpasses requires observations at different times at each station. Thus, the CCSP authors may want to reconsider this recommendation. 6. Better use of statistics is needed in lines 366-369. 7. In lines 402-407, there are at least two comments on Kalnay and Cai (2003) and there should also be a reference to Simmons et al. (2004). Several criticisms of the Kalnay and Cai approach have been identified. 8. The recommendations for “tightly constraining” the dataset for reanalyses in line 425 is not possible or wise owing to continual changes in all observations, including sondes.
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