From	Keith Briffa	Date	Mon Sep 10 20:34:13 2001
To	Edward R. Cook, Michael E. Mann
CC	Malcolm K. Hughes, Crowley_Hegerl, Jonathan T. Overpeck, ray bradley, Jan Esper, Scott Rutherford, Phil Jones
Subject	Re: Esper/Cook paper
Ed I still believe you are not showing sufficient comparisons with series besides the MBH ; necessary to demonstrate the true extent of "new" information in this work. At the very least this needs to acknowledge that other (and other tree-ring-based ) series are out there , that use at least some of the data you employ , and use the RCS method to process may of their constituent series - i.e. the Northern chronology series shown in my QSR paper. What is similar and what is different in your series and this one? You give the impression here that you are using the RCS and new data to demonstrate the possibility of getting more low frequency signal from tree-ring data - but then you base this on a comparison with MBH only. Surely what is needed here is to establish WHY MBH don't get as much LIA for example . By not showing that other tree-ring data that have also shown a LIA , and not exploring why MBH does not (despite using some of the same -and note -already RCS standardised data) is perhaps confusing rather than clarifying the issue. When we discussed this here, I also suggested the need to show separate "north" and more "south" curves ,separated in your data set, to try to get at least some handle on the independent expression of the centennial trends in a region south of the over-exploited northern network . At the very least it should be clearly stated that many of the site data used here and in previous work (see our Science perspectives piece) are common and other series already produce more low-frequency signal than is implied in MBH . Sorry for this rushed comment but I wanted to get this point over as we had talked about it before but you don't seem to have taken it on board. cheers Keith At 02:51 PM 9/10/01 -0400, Ed Cook wrote: Hi Mike et al., Okay, here is an overlay plot of MBH vs. RCS, with RCS scaled to the 1900-1977 period of MBH, and with 95% confidence limits. This has been done for the 40-yr low-pass RCS data to be consistent with the low-pass MBH series you sent me. The 95% confidence limits of the RCS are also scaled appropriately. Since correlations with both instrumental and MBH are O(0.95) after even 20-year smoothing because of the trend, the RCS limits are effectively based on the bootstrap 95% limits of the 14 chronologies. Assuming that the original RCS C.I.s are reasonably accurate (which I think they are), what is apparent (to me anyway) is that the confidence limits of MBH are uniformly narrower after AD 1600. Prior to that, they are comparable to RCS back to ca. AD 1200 where RCS C.I.s get bigger. Of course this is an odd comparison because the confidence limits are not derived the same way. However, I do think that they are somewhat informative nonetheless. What is also apparent is the much great amplitude of variability in the RCS estimates. This is consistent with the understanding that extratropical temperatures are more variable than tropical tempertures, which supports the idea that the MBH record does have more tropical temperature information in it. The other interesting thing about expressing the RCS data this way and overlaying it on MBH is the appearance that MBH is missing the LIA rather than the MWP, at least on multi-centennial timescales. This turns some of Broecker's criticism of the "hockey stick" on its head. I'm not sure where all this leads. Any comments and further suggestions are welcome as long as they come in by tomorrow. I am definately submitting the paper within a day or two. Cheers, Ed ================================== Dr. Edward R. Cook Doherty Senior Scholar Tree-Ring Laboratory Lamont-Doherty Earth Observatory Palisades, New York 10964 USA Email: drdendro@ldeo.columbia.edu Phone: 845-365-8618 Fax: 845-365-8152 ================================== -- Professor Keith Briffa, Climatic Research Unit University of East Anglia Norwich, NR4 7TJ, U.K. Phone: +44-1603-593909 Fax: +44-1603-507784 [1]http://www.cru.uea.ac.uk/cru/people/briffa[2]/ References 1. http://www.cru.uea.ac.uk/cru/people/briffa/ 2. http://www.cru.uea.ac.uk/cru/people/briffa/