cc: Julie.Jones@gkss.de, Eduardo.Zorita@gkss.de, fidelgr@fis.ucm.es, Tim_Osborn@gkss.de, k.briffa@uea.ac.uk
date: Sat, 12 Feb 2005 13:11:06 +0100
from: Hans.von.Storch@gkss.de
subject: Re: fwrd
to: "David M. Ritson"
Dear David,
we just had a good meeting in Reading, and it seems hat we really need more work to
understand all this. For the time being, a major point seems to be the usage of the
low-frequency data during the training period - which is to first order a trend and has
thus only one dgf. If we believe that the NH-trend is properly decribed by the proxy trend
in the 20th century, then everythin g is fine; If we, however, are concerned that the trend
the proxy data of the 20th century are compromised - e.g. by the fertilisation effect in
tree ring data - then we have a problem. In Moberg's recent reconstruction in nature, this
point is made very explicit - as he openly relies on the assumption that is normized
history may be scaled by the variance of the 20th century.
Your comment about the politication I found most interesting - we just had an article in
the German weekly SPIEGEL about that - see attached. Have you seen Marcel Crok's analysis
of the McIntire & Mann conflict? - also attached.
All the best
Hans
Hans von Storch
Institute for Coastal Research, GKSS Research Center
Max-Planck-Strasse 1, 21502 GEESTHACHT, Germany
ph: +49 4152 87 1831, fx: +49 4152 87 2832
mobile: + 49 171 212 2046
http://w3g.gkss.de/staff/storch; storch@gkss.de
"David M. Ritson"
11.02.2005 22:26
To
Hans.von.Storch@gkss.de
cc
Eduardo.Zorita@gkss.de, Julie.Jones@gkss.de, fidelgr@fis.ucm.es, simon.tett@metoffice.com
Subject
Re: fwrd
---------- Forwarded message ----------
Date: Fri, 11 Feb 2005 13:18:55 -0800 (PST)
From: David M. Ritson
To: Tim Osborn
Cc: k.briffa@uea.ac.uk
Subject: Re: Your Science perspective letter.
Dera Tim and Keith,
I appreciated your candid reply. My context is a
belief that the climate field is losing and has lost a great deal of
credibility over the years as to whether it is serious science. Practically any
of my colleagues in the physics department would say that things are so
politicized that they wouldn't know what to believe, but that, at some point,
if you keep adding greenhouse gasl s you are going to have a problem. The
handling of millenium temperature records certainly lends support to this
cynicism.
In the MBH instance virtually all the simple internal consistency checks.
one should expect to find, are missing. For example in the last days I pulled
the North American tree files of seventy proxies, added white noise to all
the records, and reanalysed, to check I wasn't overlooking something
obvious. Of course, well within errors, relative shapes are unaffected, whereas
the absolute normalisation goes as 1/(1+m)**.5. I failed to find a coherent
description in the literature as to where and how MBH calibrated their data
on an absolute scale. Maybe they finally regressed their results relative to
the observational data? In that case yours and Von Storch et al work would be
misleading. I had expected that you and/or Von Storch et al, could provide
the answer to this most basic question, and e-mailed both
of you, however to no avail (not that you both didn't try.). Tests
based on a SINGLE proxy are not directly responsive to MBH. SVD analysis
of a single proxy provides only one non-zero eigenvector, and it is identical
to the original parent single proxy data. A 1/(1+m)**.5 PC1 scale error
trivially, and identically, results from this.
The above is not to say that thre isn't a lot of good work, Crowley, Esper etc.
I give M&M lots of credit for stirring things up but poor marks for their
basic understanding and objectivity on many of the issues, and the same goes for
MBH. What is so damaging about the current debate as to whether current
temperatures exceed anything in the past millenium is the
poverty of the work and, by inference, the refereeing of it. Final
scientific answers seem out of current reach. Politically it should suffice
to say that the last twenty/fifty years have seen a greater NH temperature
change that in any comparable period over the last millenium.
This appears well within our scientific reach.
Sincerely,
David
On Mon, 7 Feb 2005, Tim Osborn wrote:
> Dear David,
>
> thank you for your interesting e-mail about MBH98, von Storch et al., and
> our perspective on it. With up-coming deadlines and meetings I don't have
> time for a full response unfortunately, but here are a few thoughts about
> the applicability of our perspective...
>
> You are indeed correct that the specific example we gave was on the effects
> of noise on a single proxy record. Space constraints prevented us from
> giving additional and more applicable examples, which would have been
> developed from the example we gave. Plus, our appreciation of the problem
> was only beginning to develop at that stage - and indeed our thoughts and
> ideas about the nature of the problem and how we might solve it are not yet
> settled. Nevertheless, I think that our example can equally be applied to
> the case where the combination (by whatever method) of many records into a
> single time series is used as a "proxy" for the true NH temperature. The
> "proxy" will depend upon the NH temperature plus the "noise" that arises
> from the fact that the individual records are relatively sparse and do not
> therefore sample the full NH. Like the noise in individual records, this
> "noise" due to representing the true NH by an incomplete sample will likely
> have a "whiter" spectrum than the spectrum of the real temperature, due to
> the timescale-dependent spatial correlation structure of temperatures
> variations (meaning fewer degrees of freedom at longer time scales).
>
> Sorry for the brief reply, but hope it is of some interest.
>
> Best regards
>
> Tim
>
>
>
> At 19:47 03/02/2005, David M. Ritson wrote:
> >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
> >================================================================================
>
> Dr Timothy J Osborn
> Climatic Research Unit
> School of Environmental Sciences, University of East Anglia
> Norwich NR4 7TJ, UK
>
> e-mail: t.osborn@uea.ac.uk
> phone: +44 1603 592089
> fax: +44 1603 507784
> web: http://www.cru.uea.ac.uk/~timo/
> sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm
>
>
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