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REVIEW OF CHAPTER 3

A major concern about this chapter is the repeated reference to "trends" in climate data that often are not statistically significant. A trend that is not significant at an arbitrary (say, α = .05) level is in fact not distinguishable from zero, and is therefore neither "rising" nor "falling". Thus there are several points where, in order to meet this normal scientific standard, the text must be modified.

Specifically, I recommend the following changes:

Page 1, lines 15-17: "Radiosonde, Microwave Sounding Unit (satellite), and surfacemeasured temperatures show no statistically significant change beginning in 1979. After adjustment for volcanism and El Nino, the satellite data continue to show no significant trend."

For the same reason, the last sentence on page 1 should be removed, unless the ice coverage is below the mean at a statistically significant level; it is not.

Page 2, line 2. There has been no significant trend in global precipitation...

line 11-12. I don't know if the difference since 1987 is statistically significant in terms of annual average, but you should ask Dave Robinson at Rutgers to see if this statement can stand.

Beginning on line 22. SOI values 1990-1995 are not distinguishable from 1910-1917, a slightly longer period. The statement about the behavior between 1990-95 must therefore be deleted; leaving it in will compromise the scientific credibility of the document because critics will point to the similarity between the two periods (in spite of the fact that the global temperature was lower and that the transition from 1917 to 1920--after the prolonged El Nino ended--was perhaps the most notable warming period in the entire instrumental record)

Page 3 line 3. Again, the change in extratropical cyclone activity is not statistically significant (see Dolan and Davis, 1994), so the sentence should read, "There is no significant change in strong extratropical cyclone activity, however, intense tropical cyclone activity in the Atlantic has decreased significantly".

Line 13 is profoundly misleading and will subject the report to public criticism. It conveys the impression that the composite temperature indicator (Figure 3.22) is at its highest value; it clearly is not, and the highest values were reached in the 1930s with the big rise between the 19-teens and the 20s; look at the figure. For accuracy, the text should read, "Composite indicators of summer temperature show that a rapid rise occurred around 1920, and that the 1920s and 1930s the warmest decades since at least around 1400. This rise was prior to the major greenhouse emissions. Since then, composite temperatures have

dropped slightly on a decadal scale." Again, take a look at figure 3.22 carefully.

Lines 25-26. The last sentence, while it may be true, surely is there to convey the impression that this is important. What is obviously more important is regional climate change, particularly because the projected warming is more likely to be night/winter/high latitude than anything else. There are plenty of regional changes within this magnitude range in the 20th century. Therefore the last sentence should be struck.

Page 6, lines 2-4. Combining satellite and surface data to reformulate SST is an interesting idea. You therefore should also attempt to combine the MSU and surface records, as MSU gives broader coverage. At any rate, the chapter as it stands gives those (like this author) who like to do that a perfect precedent. Combining surface and MSU records blows any significant trend out of the NH, SH and global records for the last 50 years, and reduces the century-scale warming trend by 50%. This should be noted somewhere in the

text.

Page 7, line 22. First word must be changed to "all". Cite one that does not. If you can find one or two, change to "almost all".

Line 27. The significant warming there is only in the night (winter) temperature. Change to "Significant warming of winters since the 1950s...."

Line 31Add: "Sansom (1989) [Journal of Climate] found no significant change in mean temperatures averaged across Antarctica since 1957.

In addition, analysis of surface records shows no significant trend in mean Antarctic temperatures back to 1965, or 1967 if the radiosonde record is used (see attached figure) Thus all of the power in the post-IGY record is between 1957 and 1965. This will no doubt become public knowledge when Jones 1995 hits the press, so why risk credibility by not mentioning it now?

In addition, the cold 1994 data must be included; If you're going to use it in this report to demonstrate that global temperatures were warm, you had better also include the Antarctic figures or be subject to comments about subjective data inclusion.

Page 9, lines 34-36. None of these warmings are statistically significant at the .05 level. Add a sentence. "Inasmuch as none of these trends were statistically distinguishable from zero, these figures are mutually consistent".

Page 12, line 34. Lachenbruch and Marshall hypothesized a warming of 2-4°C "sometime in the last 100 years" in their 1986 paper. There are land records available for their region of study, and they show this warming was prior to 1950, or hardly consistent with a greenhouse enhancement; In fact, this is characteristic of much of the high latitude North American borehole studies and should be noted.

Page 14, line 21. Change to be consistent with Page 9, lines 34-36 noted above. There is no significant change in any of these records since 1979.

Page 20, lines 26-40. Way to take something we didn't say and say we said it!!! Here's what the EOS paper (Lins and Michaels, 1994) concludes in its final paragraph:

"One possible explanation for the differences between Karl's findings of no (emphasis added here for the IPCC folks) increases in winter-season precipitation and our increasing winter streamflow is that there may have been a decrease in evaporation which would occur if there were an increase in cloudiness even if temperature and precipitation did not change...[cloudiness increases in the U.S. were described by Angell, 1990]...The streamflow and cloudiness data are also consistent with the trend toward lower daily maximum temperatures (and therefore less evaporation) that occurred across the United States from 1948-87".

Please make the text consistent with the citation. Try, "Their results were most consistent with observed reductions in daytime high temperature and increased cloudiness over the United States, as streamflow increases were observed over regions and seasons where precipitation has not increased".

Page 25, lines 10-14. Mastenbrook (1983) found larger declines over the same regions noted in Oltmans and Hoffman for the 1960s and 70s. Somehow this should be noted.

Page 27, line 17. Trenberth (1995) is submitted, not accepted.

Page 29, line 20. Hurrell (1995) also submitted, not accepted. Because this is cited immediately after Trenberth and Hurrell, I'll guess that they're related. While Kevin appears to know more than anyone about climate (just ask him), even his work may be subject to revision after review.

Page 30, line 26. The 60-year "period" referred to by Schlesinger and Ramankutty is based upon one (1) very noisy cycle length. Errors in hemispheric temperature projections by Schlesinger's GCM bear little resemblance to this pattern. Thus the text should be modified to indicate that the magnitude of the Schlesinger and Ramankutty period is insufficient to explain any statistically significant portion of current transient model errors in the Northern Hemisphere.

Page 32, lines 4-5. This is a decidedly "non-greenhouse"-like circulation change in the hemisphere that is supposed to be unfettered by sulfates. Contrast this to Page 33, lines 22-23. Together you must conclude, from these observations, that the circulation in the Northern Hemisphere is more consistent with a greenhouse alteration than is the Southern Hemisphere.

Page 39, line 23. In this case, both manuscripts are "submitted". Because this reviewer cannot comment on the statistical significance of these findings, they are best left out.

Page 47, line 18. Figure 3.22 is very interesting and deserves comment. The text should be altered to state, as I noted in an earlier comment, "Composite indicators of summer temperature indicate that a rapid rise occurred around 1920, and that made the 1920s and 1930s the warmest decades since at least around 1400. This rise was prior to the major greenhouse emissions. Since then, composite temperatures have dropped slightly on a decadal scale."

"Cartoon" illustration: Only statistically significant changes in observed data should be included.

REVIEW OF CHAPTER 6

My greatest difficulty in reviewing this chapter relates to evaluation of the sulfate/greenhouse transient model of Mitchell, which was used in Berlin as to ground statements that models and observations are now much more consistent. My examination of Mitchell's upcoming Nature manuscript leads to the conclusion that this model is sull producing unrealistically large warmings precisely in the region where the strongest warming is forecast: the high latitudes of the Northern Hemisphere. To perform a proper review, one would need to examine the spatial and temporal behavior of this signal. Consequently I repeatedly requested gridded transient data for this model and was explicitly refused. The grounds for refusal were not logical.

In other words, I was purposefully prevented from performing a proper review of this Chapter.

Page 6.1. Lines 1-4. This is wrong. As noted in my review of Chapter 3, there is no statistically significant trend in the radiosonde, MSU, or ground based records since their concurrence begins in 1979.

Lines 11-13. Quantitative inconsistency. It is 50 years to the middle of the next century. At a warming rate of .2 to .35/decade, the temperature rise to then is 1.0 to 1.8°, not the "between 2 and 4° warmer" given in line 13. Probably best to eliminate the statement on line 13.

Lines 37-38. The exact same mistake is repeated. .15 to .25°/decade gives a warming of from .75 to 1.25°, not the "between 1 and 2.5°" given in line 38.

Page 6.5 lines 2-3. This sulfate aerosol forcing change implies that annual unscrubbed coal combustion will double by 2050. That is doubtful on several grounds.

Page 6.5. The text should note somewhere that the Cubash et al (MPI) transient model (given as MPI CO2 anom) in figure 6.2.2 is clearly making major (approximately 6°C) errors, by simulating the high latitudes of the Northern Hemisphere too cold for roughly

its first 65 years. If this massive error were eliminated, the warming it predicts would begin long before now and there would be a considerable disparity between this GCM and reality. If this is not noted in the text, it surely will be in the public discussion following release of this report. Why not save IPCC's credibility by doing so now?

Page 6.6:

My reading of Mitchell's upcoming Nature manuscript leads me to believe that transient greenhouse/sulfate models continue to produce large warmings of the high latitudes of the Northern Hemisphere that have not been observed. To verify this in space and time requires analysis of the gridded output from this model, which was denied to me. This has severely compromised my ability to properly review this chapter.

Page 6.9, lines 3-4.

Again, Mitchell's Nature manuscript still implies a large winter warming should have taken place that is not apparent from observations. I cannot comment further because I do not have the transient output

Pages 6.10-11.

The magnitude of flux adjustments, as noted in Murphy and Mitchell (1995, Journal of Climate) in the western oceanic gyres should be explicitly stated here.

Section 6.6.1.

It is clear that regional temperature and precipitation biases are so large as to make such estimation of future climate a dangerous exercise. Why include this if it is so unreliable?

COMMENTS ON SUMMARY FOR POLICYMAKERS

SPM-1, line 8. Several opinion polls of scientists have concluded that the use of the world "already" conveys a (purposeful?) misleading impression to the (mostly) non scientists who will only read this chapter. Remove the world "already" and this criticism will not be leveled.

SPM-2, top section. I do not believe in the "basic integrity" of the models because of the large errors that are currently made in high latitude winter. This is where the greatest warming is forecast and where there has been little evidence that this forecast was cUTCCI. You should add a "bullet" after line 18 that states,

°continued overestimation of high latitude winter warming is a serious problem that has generally eluded correction, even after allowing for competing effects of anthropogenerated aerosol.

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