date: Thu, 3 Feb 2005 11:47:59 -0800 (PST) from: "David M. Ritson" subject: Your Science perspective letter. to: t.osborn@uea.ac.uk, k.briffa@uea.ac.uk Dear Tim Osborn and Keith Briffa, I read with interest (and some puzzlement) your perspective on "The Real Color .." relative to the work of Storch et al. If one was dealing with the effects of noise on a single proxy record your `perspective would make perfect sense. However the MBH98 results derive from an analysis of large families of proxies, as of course you are well aware. For instance the ITRB North American set of proxy records exceeds a number N in excess of seventy. Whatever the method of analysis, SVD or simple averaging, the extracted signal is independent of N whereas the noise contamination decreases as 1/N**.5. With seventy or so proxies, and I have veriified this with the ITRB series, low fequency noise distortion effects become small. The problems, (if there are problems), appear to lie elsewhere, for instance: 1) MBH normalize, ?calibrate, each proxy record with its detrended variance. Absent proxy-specific noise (disease, incect infestations etc) this would be problem free. However in the presence of proxy specific noise the variance is inflated by the canonical factor (1+m)**.5 where m is the ratio of proxy noise to the temperature noise, and hence their temperature scaling factors will be very significantly modified by the presence of such noies. MBH do not appear to make any mention of this? It is however calculable intrinsically from the data. Maybe MBH98, as a last anlysis step, scaled their results into agreement with the observed temperature anomaly record? If they failed to do this, analysis of their Northern tree data, shows that their temperature anomalies would be underestimated by a factor around 2.5. 2) For w5atever reason the ITRB proxy family shows qualitatively vey large differences in sensitivities and noise contamination. This of courses makes weighting and selection of data highly subjective? This, not short-segment standardization (a red-herring), lies at the heart of the M&M debate where M&M want to eliminate whole classes of tree-proxies. 3). MBH98 assume that `growth', X_i, is linearly related to real temperature anomalies for each proxy i via sensitivity factors K_i X_i=K_i*T + e where T is the temperature anomaly at time t and e is random noise. or X_i=K_i*f(t)+e where T=f(t) of course if (as seems likely) the sensitivity factor varies over centuries so that in terms of a slowly varying function F K_i=K0_i*(1+F(t)) or X_i=K0_i*(1+F(t)*f(t) +e This could equally as well be interpreted as X_i=K0_i*F'(T)+e where F'(t)=f(t)*(1+F(t) Without careful independent considerations, the presence or absence of low frequency temperature components is degenerate with growth sensitivity and, on multi-century scales, is indeterminate? I would certainly appreciate any clarifications you may have for the above. Frankly I am apalled by an apparent poverty of mechanisms in the climate field to resolve such problems, or alternatively to classify them as irresolvable? Sincerely Dave Ritson ================================================================================ David Ritson, Emeritus Prof of Physics Physics Dept Varian Physics Buiding 382 Via Pueblo Mall Stanford University Stanford, CA 94305-4060, USA e-mail: ritson@slac.stanford.edu Telephone number: 650/723-2685 FAX Number: 650/725/6544 ================================================================================