Government Comments on the Final Draft of the SPM IPCC Working ...

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<strong>Government</strong> <strong>Comments</strong> on the Final Draft of the SPM IPCC Working Group I Fourth Assessment Report No. Batch Page:line From To Comment for which it is expressly intended—that is, to indicate “recent trends which have a discernible human influence and are likely to continue in the 21st century”. Tables traditionally recapture key points in the accompanying text, and are often used as standalone presentation vehicles. Table SPM-1 should fulfill this role with respect to trends. As it now stands, only a few of the trends deemed worthy of discussion in the document are included, and one could argue they are not even the most important ones. It is recognized that the table was originally focused on extremes; but, given that it is so explicitly concerned with trends and anthropogenic influence, it gives the impression that the trends mentioned are the only ones worth highlighting as having an attributable human influence (5 out of 7 with marginal certainty). This deficiency could be corrected by either adding phenomena with more pronounced human influence or by removing the attribution column. At a minimum, Table TS-4 (TS-30, lines 1-13) should be substituted for Table SPM-1 as foundation of the editing process, because this version of the table explains the origins of the attributions. The following is a list of parameters that are mentioned in the SPM itself, with trends currently occurring and likely having a discernible human influence (or at least more likely than not) and whose trends are likely to continue in the 21st century: 1. Carbon dioxide 2. Nitrous oxide 3. Positive radiative forcing 4. Global average surface air temperature 5. Low- to mid-tropospheric temperature 6. Atmospheric water vapor 7. Global ocean temperatures 8. Global average sea level 9. Northern Hemisphere snow cover and mountain glaciers 10. Arctic sea ice 11. Greenland and Antarctic ice sheets (here one could make the point that their trend in the 21st century is uncertain, even though the trend currently is for shrinkage) 12. Increased precipitation (N. America, S. America, northern Europe, northern and central Asia; the model projections could be used to suggest whether these are likely to continue and, if so, it would increase the likelihood that the current trend is due to human influence). 13. Decreased precipitation (Sahel, the Mediterranean, southern Africa and parts of southern Asia; again use models to estimate continued likelihood and current anthropogenic influence). 14. More intense and longer droughts 15. Specific basin-scale salinity changes (in particular, if the North Atlantic is getting fresher) 16. Frequency of heavy precipitation events 17. Extreme temperatures – cold nights and frosts, hot days, hot nights, and heat waves 18. Tropical cyclones (appropriately caveated) 19. Atmospheric circulation. Omitted are items (such as methane) that do not have current trends. Adding true “climate events” provides authors with more signals to give higher degrees of certainty (including very likely, extremely likely, and virtually certain). Given the current space devoted to Table SPM-1, this list, in part or in its entirety, would fit on one page. It would provide Page 46 of 99
<strong>Government</strong> <strong>Comments</strong> on the Final Draft of the SPM IPCC Working Group I Fourth Assessment Report Batch Page:line No. From To Comment a convenient summary of both past changes, likely predictions, and the probability of anthropogenic influence. [Govt. of United States of America (Reviewer’s comment ID #: 2023-96)] SPM-430 A 7:3 7: Table SPM-1, 2nd column, last line: Why only "likely"? There could be a good reason but since mean sea level has gone up with certainty, it is hard to understand why increase in extremes is less certain, especially when it is not even quantified. [Govt. of Belgium (Reviewer’s comment ID #: 2003-32)] SPM-431 A 7:3 7: Table SPM-1, 4th column, last line: Why only "likely"? If the average sea level increases, the return period of extreme high sea level events (due to storm surges) decreases automatically, with very high likelihood. [Govt. of Belgium (Reviewer’s comment ID #: 2003-33)] SPM-432 A 7:3 7:13 A note of (e) should be added in Table SPM-1 in order to explains that the three types of likelihood in different columns have different meanings in order to avoid misunderatanding because they are derived from observation, detection and projection respectively. [Govt. of China (Reviewer’s comment ID #: 2006-24)] SPM-433 A 7:3 7:13 Table SPM-1. Please check the content of the table and the corresponding content in the text to keep them consistent, especially in the section "Understanding and attributing climate changes". [Govt. of China (Reviewer’s comment ID #: 2006-25)] SPM-434 A 7:3 7:13 In the last line of Column 1 in table Spm-1,"Increased incidence of extreme high sea level (excludes tsunamis)", what is the timescale of extreme high sea level? If it exclude tsunamis, then storm tide should also be excluded, so, what can cause extreme high sea level? [Govt. of China (Reviewer’s comment ID #: 2006-26)] SPM-435 A 7:3 7:4 It is offered to replace heading of a column 4 "Likelihood of continuation of trend based on projections for 21st century using SRES scenarios" on "Likelihood that projections for 21st century using SRES scenarios detect tendency similar to observed trend" [Govt. of Russian Federation (Reviewer’s comment ID #: 2018-8)] SPM-436 A 7:6 7:7 Table SPM-1 : the writing with "/" is not very clear warmer/fewer cold, days/nights does that mean warmer or fewer cold, days and nights? [Govt. of France (Reviewer’s comment ID #: 2010-25)] SPM-437 A 7:6 7:7 Table SPM-1 : the last bullet is not very clear "increased incidence of extreme high sea level" : does this correspond to increased sea level and its consequences on increasing the occurrence of high sea level associated with extreme meteorological conditions ? This seems also very much linked with the preceeding line on tropical cyclones. Also the word "incidence" should not be used, as it is synonimous of impacts treated by Working Group II. [Govt. of France (Reviewer’s comment ID #: 2010-26)] SPM-438 A 7:6 7:14 table SPM-1: Delete ‘discernable’ in the heading of the third column. [Govt. of Netherlands (Reviewer’s comment ID #: 2014-15)] SPM-439 A 7:6 7:14 table SPM-1, statements on droughts, tropical cyclones and high sea level: Insufficient data are available for the assessment of the likelihood of trends and human influence. [Govt. of Netherlands (Reviewer’s comment ID #: 2014-16)] Page 47 of 99
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