date: Wed Jun 8 08:57:43 2005 from: Tim Osborn subject: Fwd: Von Storch et al critique of MBH (fwd) to: "Keith Briffa" Apparently we owe Mike Mann an apology! B*ll*cks to that! Tim Date: Tue, 7 Jun 2005 18:08:14 -0700 (PDT) From: "David M. Ritson" To: t.osborn@uea.ac.uk Subject: Von Storch et al critique of MBH (fwd) Dear Tim, I pursued the question as to whether MBH does or does not constrain/force their proxy results into agreement with the observational data for 1902-1982 with Mike Mann. The answer is indeed that they calibrate by forcing this agreeement. In more detail Their basic assumption was that the `growth', X_ij for proxy i and year j was given by X_ij=SUM_m(S_mi*A_mj)+e_ij where, A_mj is the amplitude of mth EOF for year j, and S_mi is the `sensitivity' of proxy i to EOF m, and the e_ij are the associated random noise. The m EOFs are determined from the observed temperature anomaly data for 1902-1981. The sensitivity factors, S_mi are determined to best fit the 1902-1981 proxy data to the observed data. Given the S_mi, they can reconstruct the best-fit A_mj from their X_ij. Therefore, by `definition' their reconstructed signal for 1902-1981 must, within errors, agree with the original experimental temperature anomaly signal. The MBH results do indeed agree within errors with the 1902-1981 observational temperatures. Von Storch et al in their Science letter (supported by your perspective) in their Figure 2A show simulation results for 1902-1981 that qualitively very `strongly diverge from the `observed' data for 1902-1981 as a function of added white noise. One can only conclude that VS04 did not follow the MBH calbration procedures. Enclosed is some correspondance with Hans relative to this. Frankly I think Hans, and you guys, owe Mike an apology on this point? Below, unfortunately (apologies) in order of present backwards in time, is some relevant correspondance with Hans. Cheers Dave ================================Correspondance======================= ---------- Forwarded message ---------- Date: Mon, 06 Jun 2005 22:56:01 +0200 From: Hans.von.Storch@gkss.de To: David M. Ritson Cc: Eduardo.Zorita@gkss.de, fidelgr@fis.ucm.es, Hans.von.Storch@gkss.de, Julie.Jones@gkss.de Subject: Re: VS04 (fwd) Dave, I am impressed by your certainty, but I suggest that you just wait for our paper. I am actually not that stupid as you indicate. At least, I believe so. The statement "Fundamentally whenever you scale units, cm to km, ozs to kg, deg F to deg C, etc, you are "regressing a trend on a trend"." may be a bit too simple. In the meantime, I propose that you write a comment on our paper so that we can discuss that publicly - since you seem to know so well what this is about. By the way, it was MY answer not our groups' answer. All the best, Hans From:"David M. Ritson" Sent:06.06.2005 22:27 To: Hans.von.Storch@gkss.de Dear Hans et al, Thanks for your reply which clarifies your group's position. Fundamentally whenever you scale units, cm to km, ozs to kg, deg F to deg C, etc, you are "regressing a trend on a trend". MBH, in terms of your simplified model, use a thermometric scale based on the tree-ring sizes, and then, entirely correctly, they calibrate the proxy temperature scale relative to the observational absolute temperatures from 1902 to 1981. This is exactly what students do in elementary lab classes when they fabricate thermometers, do an experiment and finally calibrate their fabricated thermometers against a calibrated thermometer. Your group according to your e-mail, omitted the calibration step. Under such circumstances results are necessarily meaningless. I feel embarassed to be going into such elementary considerations with you of all people. From a formal statistical point of view when you regress a gradient against a gradient intrinsic errors from a single measurement are indeterminate, ie you are dividing zero chisquared by zero degrees of freedom. Of course extrinsic errors exist and are readily found from an ensemble of measurements, and/or from the errors associated with the procedure used. In actuality MBH98 used a more sophisticated procedure. They had eighty annual measurements they regressed against, and as outlined in my previous e-mails they calibrated sensitivity factors to a few leading EOFs derived from the observational data. This of course does not change the gut argument. MBH98 calibrated their proxy temperature scale, and according to your communication your group omitted this step in your simulation of MBH procedures. I certainly feel, in view of the scientific and media attention to your letter, that it is essential that this omission be fully clarified to the scientific community and that such a clarification would be most meaningful if it came directly from you people. Sincerely Dave On Sun, 5 Jun 2005 Hans.von.Storch@gkss.de wrote: > David, > > we had something prepared for this question for another comment we got on > our science paper. This comment was eventually no accepted for pu > blication, and we will have now all this in a separate publication of our > own. This is work in progress and we will make this available as soon as > we are done. You know that Mann had withdrawn his comment on our article > recently - after he had told journalists long ago that it was already in > press. > > The answer in a nutshell is: Thou shalt not regress a trend on a trend. > Or, in other words - a stats model based on 1 dgf can not be statistically > be justified (but maybe physically). A fundamental and most meaningful > principle of statistics. > Cheers > Hans >