date: Mon, 16 Jun 2003 07:58:55 +0100 from: Phil Jones subject: Fwd: 2003JD003695 Decision Letter to: k.briffa@uea.ac.uk,t.osborn@uea.ac.uk >Subject: 2003JD003695 Decision Letter >From: jgr-atmospheres@agu.org >Reply-to: jgr@envsci.rutgers.edu >Date: Sun, 15 Jun 2003 23:36 -0400 >To: p.jones@uea.ac.uk >Cc: > > >Dear Phil: > >Below please find 3 reviews of your paper "Changes in the Northern >Hemisphere annual cycle - implications for paleoclimatology?." The >reviewers have suggested revisions to your manuscript. Please take the >reviewers' remarks into consideration and adequately address their >questions and concerns with a revision of your manuscript. > >Please submit your revised manuscript and a detailed response to each >question and comment of the reviews. The revised manuscript must be >returned within one month of receipt of this letter. Failure to meet this >deadline may result in the revised manuscript being handled as a new >submission. If you feel that you cannot address all comments and revise >the paper within one month, please contact me immediately. > >When you are ready to submit your revision, please use the link below. > > > > >(NOTE: The link above automatically submits your login name and >password. If you wish to share this link with co-authors or colleagues, >please be aware that they will have access to your entire account for this >journal.) > >Please note that all parts of the manuscript must be double-spaced and >single-sided (including references, figure captions, and tables). Also, >the references need to be on a page of their own, separated from the text >of the manuscript. For further information on all editorial policies, >please see our homepage at http://www.envsci.rutgers.edu/jgr > >Thank you for choosing the Journal of Geophysical Research - Atmospheres. > >Sincerely, > >Alan Robock >Editor, JGR-Atmospheres > >------------------------------------------------------------------------------ > >At http://agu.org/pubs/au_contrib_rev.html for full instructions on how to >prepare your final manuscript text file. > >For information regarding manuscript image requirements, please go to >http://agu.org/pubs/guides3a.html. It is critical that the correct image >file formats are submitted. Particular attention should be paid to figure >resolution, line weights and color/grayscale requirements. Color figures >that will appear as such in the print version of the journal should be >submitted as CMYK. Images that will appear in color only in the HTML >version on-line may be submitted in RGB. > >For a complete description of the color options available for publication >in JGR-Atmospheres, please go to >http://agu.org/pubs/journal_forms/colorpricing.html > >Publications Charges Form, Copyright Form and Reprint Forms may be >downloaded for completion and sent to AGU before your article may be >published. The Publications Charges form also includes the NEW color >pricing options which were revised in May 2002. >(http://www.agu.org/pubs/journal_forms/PUBOPT_JGR02.pdf) > >All forms and purchase order or payment must be received prior to >publication. Accordingly, please mail and/or fax the completed forms as >soon as you know that your manuscript is accepted. If you need assistance >with file formats please e-mail jgr_atmospheres@agu.org (Natalie Reid) and >quote your manuscript number. For more information on color charges, >please contact Natalie Reid or author.help@agu.org. > >If you need Adobe Acrobat Reader to download the forms, it is available, >free, on the internet at: http://www.adobe.com/prodindex/acrobat/readstep.html > > >------------------------------------------------------------------------------ > > >Reviewer Comments > >Reviewer #1 Evaluations: >Assessment: Category 1 >Ranking: Excellent > >Reviewer #1(Comments): > > The authors of this manuscript are known as the best empirical > climatologists of the modern world. In this paper they found that > winters have warmed relative to summers during past two centuries > compared to earlier part of the millennium. The paper discusses possible > mistakes in interpretation of proxy, preinstrumental, climatic records > related to seasonal cycle in climatic trends. And, we know that such > mistakes are common in paleoclimatic reconstructions. > The paper is short, well written and properly illustrated. I > expect that it will be interesting for many readers of JGR-Atmosphere. I > recommend it to be published as is. > > >Reviewer #2 Evaluations: >Assessment: Category 2 >Ranking: Very Good > >Reviewer #2(Comments): > >General Comments: > >This is an interesting manuscript, raising some important issues >regarding seasonality of past temperature trends that are interesting in >there own right, and may have potential implications for certain >paleoclimate reconstructions. These issues are worthy of discussion in the >literature, and JGR is an appropriate venue. The authors, as is typical, >have done a careful job with their analysis, and it appears sound, as do >the primary conclusions, although I have some specific reservations. The >primary criticism is that the authors imply a greater generality to their >conclusions than can actually be justified, given the limitations of the >available data series. There are a number of important caveats that need >to be invoked in the interpretation of the results, and the limitations in >drawing large-scale conclusions from the limited data need to be >acknowledged up front. There are a number of underlying issues regarding >the nature of the seasonal and spatial details of past climate change (in >particular, forced climate change) which likely impact the interpretation >of the results, which are not given adequate discussion in the manuscript >at present. Given the space available in a JGR paper (vs. e.g. a GRL >article), there is no excuse for not providing more detailed discussion >where appropriate. I provide several specific comments below along these >lines which should be addressed in a revised version of the manuscript. > >Specific Comments > >1) Abstract--the generality of the conclusions are overstated in the >abstract. The evidence is only from Europe and China (i.e, only the >fringes of the Eurasian continent alone) but the wording argues that >implications apply to other regions. It isn't even clear that the >conclusions apply to the interior of the Eurasian continent, let alone any >of North America (see comments below). It is a leap of faith, then, to >assume that the results generalize to extratropical hemispheric (let >alone, full hemispheric) trends, and the authors need to be more cautious >in drawing general conclusions. > >2) Introduction, first sentence: There is a potential "straw man" argument >being introduced here. Precisely which "annual temperature" >reconstructions are being referred to here? The statement made could >arguably apply to Crowley and Lowery (2000), which is based on scaling a >composite of largely extratropical (and mostly summer-sensitive) proxy >records against the annual mean Northern Hemisphere mean instrumental >series. It is far more difficult, however, to argue that the authors' >statements fairly characterize the Mann et al (1998;1999) annual mean >temperature reconstruction. In the latter case, half of the area of the >hemispheric mean surface temperature reconstruction comes from tropical >latitudes (i.e., latitudes below 30N), and the proxy indicators primarily >used to calibrate the tropical annual-mean patterns of variance are almost >certainly not boreal warm-season in nature (for the example, the >ENSO-scale patterns of tropical SST variance in the reconstruction are >calibrated, in large part, by a combination of cold-season drought >sensitive tree-ring data from Mexico, tropical tree-ring data, and >tropical corals and ice cores--none of which could be argued to exhibit a >boreal warm-season sensitivity bias!). The authors arguments cannot be >argued to apply to these reconstructions (as seems to be implied by later >comments--see below). > >3) Discussion of Figures 1 and 2 on pages 5-6: the authors should compare >a single long-term composite series based on averaging the various >(potentially, standardized) station JJA-DJF series with that which is >available for the full NH back through the mid 19th century. The point >here is to see how well they compare in terms of the general trends >during the interval (back through the mid 19th century) of overlap--in >fact, based on inspection of e.g. Figure 1, I don't think that there will >be much similarity, and, if that is the case, then it demands extreme >caution in generalizing about the true large-scale or hemispheric nature >of inferred trends in summer-winter temperature differences based on the >sparse long series available to the authors. > >4) Related to point #3 above, recent studies (see e.g. the discussion in >the Mann, 2002 piece which is in the reference list but not actually >cited in the text, and also the results of Shindell et al, 2003) have >shown that large seasonal differences in temperature trends are expected >in past centuries because of the seasonally-specific response, in >particular, to volcanic forcing (see Kirchner et al, 1999). The largest >seasonal differences are likely to occur in the continental centers, where >volcanic forcing tends to impart a large summer cooling but also typically >a sizeable dynamically-induced warming (related to the response of the >Northern Annual Mode, or 'AO' or 'NAO' to volcanic stratospheric aerosol >forcing) in the following winter The large differences, however, are >observed over the continental centers, and in fringe regions such as >Europe or China, the response may not even be of the same sign as the >continental mean response, which is dominated by the behavior of the >continental centers. Thus, any spatial network (proxy or instrumental) >which exhibits a bias with respect to the sampling of the continents is >likely to exhibit a bias in terms of the estimate of summer-winter >temperature differences (Mann, 2002). Since the authors instrumental >network only samples the fringes of the Eurasian continent, it is very >unlikely to capture the true winter-summer difference in Eurasian >continental mean temperature, let alone Northern Hemisphere extratropical >continental (Eurasia and North America) temperature, let alone Northern >Hemisphere extratropical mean (land and ocean) temperature, let alone true >Northern Hemisphere (tropical and extratropical, land and ocean) >temperature! Once again, this calls for caveats in the interpretation of >the present results with regard to hemisphere-scale implications. > >5) Related to the above, why don't the authors show, in Figure 1, the >results for some of the long available North American series (which >includes several long east coast series, but also a series in Minnesota >back to the early 19th century) to establish the similarity of the >longer-term summer-winter trends in the two continents (this too should >be included in the composite discussed in point #3 above). > >6) End of first paragraph on page 6, the authors might note that certain >modeling studies (Shindell et al, 2003) have indeed already looked at >potential seasonally-distinct temperature changes in past centuries, that >are associated with the seasonally-distinct signature of the response to >known natural climate forcings. > >7) Figure 3 indicates a relationship that holds during the latter 20th >century, presumably somewhat specific to the mix of internal and forced >variability that dominates over that period. This may not be >representative of the situation in earlier centuries, where the primary >pattern of forced variability is by volcanic and solar forcing which >impart distinct regional and seasonal signatures in the temperature field >(see Shindell et al, 2001;2003) that are likely to be quite different from >those associated with anthropogenic forcing (GHG and aerosol) which >dominate during the interval examined by the authors. Related to this, >have the series been detrended before calculating the correlations shown >in Figure 3? This has a bearing on the interpretation. > >8) 3rd paragraph on page 7, the discussion of previous work (e.g. Mann et >al, 1998;1999) here is misleading for the reasons spelled out in point #2 >above. The arguments assuming a warm-season sensitivity bias do not apply >to the full hemispheric reconstruction but, at most, the extratropical >component of the reconstruction. The statement (2 sentences up from >bottom of paragraph) "Their implicit assumption that the relative >trends..." is not a fair statement in reference to the Mann et al >multiproxy reconstructions, and the discussion needs to be revised here. >An analysis (Rutherford et al, to be submitted) shows, using a common >statistical method, but distinct data sets, that the multiproxy network of >Mann et al calibrates and cross-validates cold-season variability more >skillfully than the tree-ring maximum latewood density ('MXD') density >network of Briffa and coworkers, while the Briffa et al MXD network, in >turn, calibrates warm-season variance more skillfully than the multiproxy >network. In short, the conclusions drawn here don't apply to >reconstructions of tropical surface temperature variability, nor to >multiproxy data used to reconstruct that variability, so the implications >of the authors results for multiproxy reconstructions of full Northern >Hemisphere annual mean temperature are not clear. The authors need to >downplay their conclusions in this regard. > >9) The authors and this reviewer are in common agreement that >seasonally-specific biases are likely to be present in most climate proxy >data, and that these biases need to closely considered in the process of >climate reconstruction. This is a fair point, and one worth emphasizing in >the conclusions But the specific conclusions of the authors in this study >regarding summer-winter differences based on the series analyzed do not >clearly generalize to other proxy-based surface temperature >reconstructions (particularly multiproxy reconstructions with an equal >tropical and extratropical emphasis) for the reasons spelled out above, >and this point, in fairness, should be made. > >REFERENCES: > >Kirchner, I., G.L. Stenchikov, H.-F. Graf, A. Robock, and J.C. Antuna, >Climate model simulation of winter warming and summer cooling following >the 1991 Mount Pinatubo volcanic eruption, Journal of Geophysical >Research, 104 (D16), 19039-19055, 1999. > >Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar >forcing of regional climate change during the Maunder Minimum, Science, >294, 2149-2152, 2001. > >Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar >forcing of "Little Ice Age" Surface Temperature Changes, Journal of >Climate, in press, 2003. > > >Reviewer #3 Evaluations: >Assessment: Category 1 >Ranking: Excellent > >Reviewer #3(Comments): > >Review of Jones et al. : "Changes in the Northern Hemisphere annual.." > >This paper addresses a very important problem in contemporary climate >record analysis. It points out that several recent reconstructions of NH >climate over the last thousand years might have some biases. The point >being that the proxies used in those analyses were perhaps more sensitive >to summer conditions than to mean annual conditions. This while recent >instrumental records tell us that the winter temperatures are responsible >for most of the warming in the annual average records. > >The present authors present data from several sites with 200-year records >where instrumental (and other fairly reliable) data show that it is indeed >the winter temperatures responsible for most of the recent climate change. >I believe this is an extremely important contribution toward our gaining a >better understanding of past climate records. > >The paper is well written and to the point. It can be published as is in >my opinion. > >Caveat: I consider myself an expert on the overall problem of climate >change, but I am not an expert in the details of the kind of data analysis >involved in this project. It would be well to have another referee who is >more versed in the arcane methods used in these analyses. > > > > Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------