Tuesday, April 10, 2012

3280.txt

date: Mon, 18 Aug 2008 12:58:09 -0400
from: Michael Mann <mannatXYZxyzeo.psu.edu>
subject: Re: Revised version the Wengen paper
to: Phil Jones <p.jonesatXYZxyz.ac.uk>, Gavin Schmidt <gschmidtatXYZxyzs.nasa.gov>

Phil (and Gavin),
there is one more big problem in the current draft. the borehole section is hugely
unbalanced. it is truly awful, and this was never dealt w/ in the previous revisions. I
can't sign my name to a paper that has such a whitewash treatment of borehole data (this
section looks like it was written by Pollack and Gonzalez-Rouco, w/out any of
acknowledgment of the many problematic issues that have been raised by others). At a very
minimum , for my name to remain on this paper, the following changes need to be made.
Please let me know if you have any questions or comments about the changes. I feel I must
state this as being mandatory for inclusion of my name in the paper. I can't sign my name
to a grossly misbalanced discussion of borehole data. I hope you understand this,
mike
1. 2nd paragraph, page 44, first sentence:
Borehole reconstructions have particular value because they do not have to be calibrated
against the instrumental record and because temperature itself is measured directly.
should be changed to:
Borehole reconstructions have an advantage in that they arguably needn't be calibrated
against the instrumental record because they measure temperature itself is measured
directly. However, a disadvantage is that, as discussed above, they measure GST rather than
the desired quantity (SAT), and under certain conditions there may be substantial
differences between the two (see below).
2. last paragraph of section, last two sentences (bottom of page 44/top of page 55)
Mann and Schmidt (2003), suggested that GST reconstructions may be biased by seasonal
influences and snow cover variability, an interpretation contested by Chapman et al.
(2004). Thousand-year simulations by Gonz�lez-Rouco et al. (2003, 2006) using the ECHO-G
model suggests that seasonal differences in coupling are of little significance over long
time scales.
this is not correct. Mann and Schmidt (2003) show that there is a potentially very large
seasonal bias in estimating winter SAT from winter GST, and any time that winter and summer
trends are not similar (which they *happen* to be in some fairly unrealistic simulations
such as Gonzalez-Rouco et al) this might not appear to be a problem. But in general, it is
a huge problem!. Confidentially, we have a paper we will be submitting soon that provides
an example (simulated early through mid holocene changes) where the impact of the snowcover
GST bias on annual mean GST is huge, and leads to a highly biased assessment of past SAT
changes from GST trends. More on that soon. But in the near term, it suffices to
acknowledge the problem first hinted at by Mann and Schmidt, by revising the paragraph
above to:
Mann and Schmidt (2003) show that GST estimates during the winter season are biased by
seasonal influences related to changing snow cover, and that less that 50% of the total
spatiotemporal variance in GST is explained by SAT variations during the cold half of the
year. Chapman et al. (2004) contest the implications this has for recent temperature trends
[contested in turn by Schmidt and Mann (2004)], and some long-term simulations [e.g. by
Gonz�lez-Rouco et al. (2003, 2006) using the ECHO-G model] suggests the possibility that
seasonal differences in coupling might be of little significance over long time scales as
long as temperature trends are similar in different seasons. However, in cases where there
are large seasonal differences in climate trends (a possibility that remains for the past
few centuries--see Mann et al, 2003) such seasonal bias issues could lead to misleading
inferences regarding long-term SAT trends from indicators of past GST change.
References:
Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., [1]Optimal Surface
Temperature Reconstructions using Terrestrial Borehole Data, Journal of Geophysical
Research, 108 (D7), 4203, doi: 10.1029/2002JD002532, 2003.
Schmidt, G.A., Mann, M.E., [2]Reply to comment on ``Ground vs. surface air temperature
trends: Implications for borehole surface temperature reconstructions'' by D. Chapman et
al., Geophysical Research Letters, 31, L07206, doi: 10.1029/2003GL0119144, 2004.
Phil Jones wrote:

Dear All,
Here's the revised version of the paper, together with the responses to the
reviewers.
We have told John Matthews, that we will get this back to him by the beginning
of next week. To us in the UK this means Aug 26/27 as next Monday is a national
holiday. So, to those not away at the moment, can you look through your
parts and get any comments back to us by the end of this week or over the
weekend?
Can you also look at the references - those in yellow and let me know of
any that have come out, or are able to correct those that I think just look
wrong?
I hope you'll think of this as an improvement.
Cheers
Phil
Prof. Phil Jones
Climatic Research Unit Telephone +44 (0) 1603 592090
School of Environmental Sciences Fax +44 (0) 1603 507784
University of East Anglia
Norwich Email [3]p.jones@uea.ac.uk
NR4 7TJ
UK
----------------------------------------------------------------------------


--
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: [4]mann@psu.edu
University Park, PA 16802-5013

website: [5]http://www.met.psu.edu/dept/faculty/mann.htm
"Dire Predictions" book site: [6]http://www.pearsonhighered.com/academic/product/0,3110,0136044352,0
0.html

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