date: Thu, 8 Feb 2001 12:52:28 -0000 from: "Julia Uppenbrink" subject: your article to: , Dear Phil and Tim We have received the reviews for your article (see below). The official letter, copyright form, and hard copies of the reviews and the marked copy follow by mail. I enclose here also an edited copy of your article; it would perhaps be best if you used this electronic copy to enter your revisions. I have used the "Track Changes" and "Comments" features, so please make sure that you can view all my changes and queries. Please let me know if anything is unclear, and send your revision within 3 weeks. Note that the text should be shortened somewhat; I think the NH Temperatures section could be pulled together somewhat, as could the ENSO section. Thanks again for writing this interesting article for us. Best wishes Julia --------------------------start of reviews---------------------------------- Review 1: This ms. is excellent and merits publication as is. In face of the ongoing discussion about the recent global warming and its cause(s), this paper provides the necessary critical review of the records to address the issues. The much quoted Mann et al. paper (Nature 1998) was critizised for the lack of such a discussion, and I am profoundly thankful for Briffa et al to have taken the time to correct the situation. With this publication the climate interpretations with respect to the last two decades and their cause can no longer be denied. Review 2: This is an excellent summary of the state of our knowledge, at present, of climate during the past millennium. I think that the tone of the article and level of detail are appropriate for a Science review article. The authors have done a thorough job of reviewing the recent progress in proxy-based climate reconstructions of the past several centuries-to-millennium, and have placed appropriate emphasis on regional variations and patterns, as well as hemispheric/global indices of climate change. There is a good balance between discussing what is known, and acknowledging the significant uncertainties that still remain. I encourage publication with only some very minor revisions. Some specific comments/suggestions are indicated below. Given the very close overlap in content, it would be appropriate for the authors to cross-refer to a very similar review article in the press and due out soon in the journal "Weather" published by the Royal Meteorological Society [Mann, M.E., Climate During the Past Millennium, Weather, in press, 2001]. This latter article also summarizes the recent evidence for changes in hemispheric mean temperature, ENSO, and the NAO over the past millennium from paleoclimate reconstructions and comes to similar, though not identical, conclusions. There is also a section on long-term drought variations, a subject which the authors here choose not to discuss. A preprint is available over the web, and galley proofs are available from M. Mann by request. 1) 1st paragraph of intro: there is, of course, a connection between our ability to provide seasonally-specific climate histories at the regional scale and our ability to reconstruct patterns related to ENSO, the NAO, "PDO", etc. I would argue that if we could do the latter well (which we can't quite at present), we could probably do the former quite well also. In other words, the authors might want to draw a more specific relationship between the comments in the middle and end of this paragraph. 2) page 4, second paragraph, sentence "Studies based...can be reliability reproduced...". There is a very important caveat that should be stated here. This presumes that the covariance structure of temperature variability of the 20th century is the same as that in the past. There are good reasons this may not be true. The pattern of anthropogenic warming represents a larger-scale warming that that found in patterns of natural variability, and thus the studies in question may underestimate the degree of spatial detail necessary to capture large-scale patterns of climate variability prior to the advent of anthropogenic warming. In short, the assumptions implicit here are not that different, at all, from the assumptions discussed in the subsequent paragraph, and this should be recognized. 3) bottom of page 5/top of page 6, statement "...(of which a number are in common to each study)". While this is factually correct, it is important to note that the key indicators (multi-millennial length high-elevation western U.S. tree ring width chronologies) which largely carry the Mann et al reconstruction prior to AD 1400 are not used in any of the other studies. In this sense, the estimates are more independent than is implied w/ the present wording. 4) page 7, 1st paragraph and footnote #25, comparison of Mann et al and Jones et al southern hemisphere temperature reconstructions: I think it is important to emphasize the difference in the target series for the two cases. Even though both are called "Southern Hemisphere mean", the Mann et al series is essentially, by construction, a southern hemisphere tropical mean series, while the Jones et al series is much more of an extratropical mean series. This is a smilar, but an even more extreme, distinction than in the corresponding Northern Hemisphere mean series, and the first sentence of the paragraph hints at this, but doesn't quite do justice to the extent of the distinction. There is a large correlation between the S. Hem and N.Hem series in the Mann et el reconstructions largely because the target regions both contain substantial coverage in the tropics (and the s.hem and n.hem tropics vary essentially in synchrony). The interhemispheric correlations cited in (25) would be found in the instrumental record itself given the two very different latitudinal emphases of the southern hemisphere estimates, and should not be attributed to the reconstructions or underlying proxy data per se, but, rather, the target region. 5) In 26 cite also the accompanying commentary [Mann, M.E., Lessons For a New Millennium, Science, 289, 253-254, 2000] which further expands on some of these issues, as well as Bradley, R.S., 1000 Years of Climate Change, Science, 288, 1353-1355, 2000 which discusses various possible alternative interpretations of the roles of forced and internal variability in governing the spatially-complex patterns of climate change over the past millennium. 6) How about changing (last sentence, bottom of page 8) "Despite the caveats..." to "Acknowledging the caveats..."!! 7) page 9, discussion of Stahle et al vs. Mann et al: It would be appropriate to mention that the two reconstructions are correlated (see Mann et al, Earth Interactions, 2000) at about r=0.6 during both calibration and pre-calibration periods, which is not that different from the numbers (r=0.7; see footnote #36) cited for their instrumental counterparts! 8) page 9. It is worth noting that Urban et al [Urban, F.E., Cole, J.E., Overpeck, J.T., Influence of mean climate change on climate variability from a 155-year tropical Pacific coral record, Nature, 207, 989-993, 2000] note (see also Mann et al, Diaz El Nino book, 2000) a breakdown of interannual ENSO variability (i.e., perhaps a collapse of the typical delayed oscillator mechanism) in the early/mid 19th century, but a persistence of decadal variability through that period, which may explain the variations in the warm and cold event frequency statistics. 9) page 10. It is essential to also acknowledge in (42) the recent paper by Cullen et al [Cullen, H., D'Arrigo, R., Cook, E., Mann, M.E., Multiproxy-based reconstructions of the North Atlantic Oscillation over the Past Three Centuries, Paleoceanography, in press, 2001] which presents some other alternative proxy-based reconstructions of the NAO and compares, more rigorously than in any other published study, the similarities and differences therein, and points out some serious flaws in the conclusions of ref #43 (the authors might also like to attempt pers. comm. w/ E. Cook on this matter). 10) Concluding remarks: amen! (especially the last paragraph!) ------------------------------end of reviews-------------------------------- ============================================== Dr. Julia Uppenbrink Senior Editor, Science (Europe Office) 82-88 Hills Rd, Cambridge CB2 1LQ T +44 1223 326500 F +44 1223 326501 E juppenbrink@science-int.co.uk visit our website: www.sciencemag.org submit electronically: www.submit2science.org ============================================== Attachment Converted: "C:\EUDORA\Attach\Jones edited.doc"