From: mann@snow.geo.umass.edu To: k.briffa@uea.ac.uk, mann@geo.umass.edu, mhughes@ltrr.arizona.edu, rbradley@geo.umass.edu, t.osborn@uea.ac.uk Subject: oops typo. disregard previous message Date: Wed, 14 Apr 1999 16:06:45 -0400 (EDT) Dear Tim, Thanks for your comments. Some responses to them are given below. I'll be too busy for further correspondance as I prepare for travel, leaving Friday morning for a week. Since I will be away and unreachable through next wednesday. I would thus request that you and Keith correspond with my co-authors Ray Bradley (who should be able to respond upon his return from current travel on Sunday /Monday) and Malcolm Hughes on the revisions (please cc to me so I can read upon my return), as I will be unreachable. I'm sure we can come up with something mutually agreeable to all of us with this piece, as is my goal with IPCC, as long as their is proper communication and mutual understanding by all concerned. Lets strive for this--choice of language is a nontrivial element... best regards, mike. ____________________________COMMENTS________________________ One additional new comment: 0) 1st page, "In attemping to do this...Mann at al...exemplifies" is unacceptable language to us. We confront the very problems that are being discussed here, so it is a disservice to us to say our paper "exemplifies" these problems. It "exposes" or "confronts" would be fair language, but "exmemplifies" is unacceptable. responses to your responses to my original comments: 1) I'm not sure how to interpret your response vis-a-vis my original comments here. My point is that our use of southern hemisphere records in the reconstructions is fundamentally sound, from the point of view of some very basic principles of optimal interpolation, etc., and given the domain we are reconstructing, which is not NH only, although we diagnose NH from our pattern reconstructions as a key index. There is no basis for what sounds like a criticism of our use of such data. I couldn't tell if you were agreeing with this or not from your commments. 2) The uncertainties are determined from the uncalibrated variance given a certain predictor network. The predictor network is unchanged from 1820 to present, so the verification period (1854-1901) unresolved variance is an independent check on the calibration period unresolved variance. Both gives numbers in the range of 30% for the NH mean temperature reconstruction, meaning that the error bars we determine from verification period are essentially the same as those we determine from the calibration period. IN this sense, the error bars as determined from calibration and verification are essentially identical, The bottom line, if we had used the verification period to estimate the error bars, the eye would barely see the difference. There may be a considerable misunderstanding on your/Keiths part, regarding regarding what is actually shown by the spectrum of calibration residuals in our GRL paper. It does not in any way conflict with what I indicate above. What this particular diagnostic shows is that there is no evidence of any increase in unresolved secular variance (ie century-scale and longer) in our reconstructions at least back to 1600. In contrast, there is evidence that such frequencies are not as well resolved as higher frequencies with the sparser predictor network available before 1600. Our estimates of uncertainty TAKE THIS FACT *EXPLICITLY* INTO ACCOUNT. Our uncertainties estimates are made up of two components that add in quadrature, including a component of uncertainty in the lowest-frequency variability as estimated from the spectrum shown, and a component of the highest-frequency variability from the spectrum shown. THese are approximated as a step-wise break in the mean (white noise) level of unresolved variance at the edge of the secular band. Unlike any previous study, we have actually estimated the increased uncertainty due to the loss of low-frequency variability as it can best be estimated, and this is explicitly incorporated into our error bars, which is why those error bars expand considerably before 1600. This is discussed in the GRL paper, and is a VERY important fact. It would be very unfortunate if this fact were misrepresented! 3) I'll leave this to Keith and Malcolm to discuss (Malcom?). I think it is pretty clear in the paper what our assumptions are here, and what the justification is of those assumptions. There is of course room for differing opinions on this stuff, as it is all somewhat speculative, and we indicate that this is so in our paper. 4) good enough 5) I really doubt that the 2000 year trend is meaningful and, unlike the results we have shown, there is no confirmation that these 3 sites accurately reflect northern hemisphere mean temperatures to any reasonable level during the modern era. Work by us and others looking at similar data would suggest that series in such regions are not adequately representative of the largest-scale trends. There is, further, no verification of the frequency-domain attributes pass any satisfactory test. For these reasons, I have informed Julia Uppenbrink directly that I don't believe this series should be shown in this context. I agree it is an important series, and it will be appropriate to discuss it in IPCC. But it should not be considered on a par with more statistically-verified true Northern Hemisphere mean temperature reconstructions, and it is very misleading to show it along with the NH mean reconstructions. The 2000 year trend runs absolutely counter to everything we know about the mid holocene. Extratropical Northern Hemisphere summer temperatures should have been at an absolute peak 4000-6000 ybp, and the 2000 year trend *ought* to at least be heading in that direction. The fact that is doesn't, and that the trend hasn't been verified in the sense discussed above, causes me real concern. It would be misleading to argue we have any reason to believe that NH mean temperatures have done what that series does 2000 years back in time... Re, the adjustment of the series, I believe it is fundamentally unsound. Essentially, agreement over the period we can best constrained (20th century) has been sacrifices for agreement during the period we can't constrain, apparently for the sake of getting the different series to align during the 19th century. Please download the figures I have prepared for the latest IPCC report. ftp://eclogite.geo.umass.edu/pub/mann/IPCC/nhemcompare-ipcc.gif OR ftp://eclogite.geo.umass.edu/pub/mann/IPCC/nhemcompare-ipcc.ps You will see how I have aligned the series based on a 1961-1990 reference period for the instrumental series, and a 20th baseline adjustment for the alignment of all series. To me, this is the most reasonable adjusment of the series if they are to be shown together. It also shows the different that latitudinal variations make EXPLICITLY by showing the difference between our TRUE (0-90 lat weighted) NH annual mean temp series, and an extratropical (30-70 deg lat) average from our pattern reconstructions, which approaches quite closely the Overpeck et al '97 and Jones et al '98 series. Seasonal distinctions then the key remain difference. This is, I believe, the best approach to the comparisons, and the one I will favor in IPCC. The alternative is that true NH mean temperatures and extratropical NH mean temperatures must be shown on separate plots, because adjusting them the way Keith has provides a misleading picture, and one that I don't believe can be justified for the purposes of IPCC, regardless of what you choose to do with your Science piece.