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

<strong>Government</strong> <strong>Comments</strong> on the Final Draft of the SPM
IPCC Working Group I Fourth Assessment Report
No.
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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
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