Thursday, December 22, 2011


From: Keith Briffa <>
Subject: Re: GKSS results
Date: Fri Oct 13 16:36:51 2006
Cc: Tim Osborn <>

Tim and I have discussed this round and round and our response is attached
what do you think
best wishes Keith
At 17:33 10/10/2006, you wrote:

Dear Tim/Keith,
I hope all is well with both of you.
We've been doing a number of sensitivity tests w/ RegEM using both the CSM simulation,
and now more recently the GKSS simulation data we got from you. There are some
methodological developments we'll describe soon, related to what is the most reliable
regularization method in RegEM, ridge regression and truncated total least squares. We
are now leaning towards the latter because of potential non-convergence problems in some
cases w/ the former. More on that soon.
More relevant, however, are the results. As you can see from the attached plot, RegEM
works quite well w/ GKSS, using a short calibration period (1900-1980, corresponding to
years 900-980 in the attached plot) and both white and red pseudoproxy noise (we used
rho=0.5 in the attached, but similar result for other values).
The most interesting result is that while RegEM reconstructs the full NH series well
throughout, in the case of the CSM simulation, it does modestly underestimate the warmth
of the earliest centuries in the GKSS Erik simulation (it fits everything else,
including the LIA cooling, very well). We feel that this is likely due to problem of
correctly identifying the 'drift' pattern using CFR methods.
The long and short of this is that we would like to be able to show this result in a
(very short!) J. Climate response we need to finalize, to a comment on Mann et al (2005)
J. Clim by Zorita and Von Storch. We would show you this response for comment of course,
and would add you as co-authors. We have cleared with Andrew Weaver that this would be
an acceptable course of action. We are hoping you are in agreement with this?
please let us know ASAP, we have to finalize our response within days.
Michael E. Mann
Associate Professor
Director, Earth System Science Center (ESSC)
Department of Meteorology Phone: (814) 863-4075
503 Walker Building FAX: (814) 865-3663
The Pennsylvania State University email:
University Park, PA 16802-5013

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909
Fax: +44-1603-507784



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