cc: Phil Jones , Keith Briffa , Caspar Ammann
date: Mon, 14 Feb 2005 11:28:11 -0500
from: "Michael E. Mann"
subject: Re: WSJ
to: Tom Wigley
Hi Tom,
Thanks--we've done all of this. We've shown on RealClimate (and in press J. Climate paper
by Rutherford et al) that the result is completely robust with respect to whether or not
PCA is used at all to represent the tree-ring networks. So its a spurious issue, claim. I
mentioned this in an email exchange w/ Gabi and others. This was copied to Francis, so I'm
very surprised to see him quoted in this way.
Ammann and Wahl will be independently responding to MM in the near future (in "Climatic
Change" it appear), and their code will be online.
We and others of course have done Monte Carlo on RE, there is somethin very wrong in their
estimation of the significance levels. Hard to know just what they did--it obviously didn't
get a real review.
travelling for a couple days. That's all I can say for now.
mike
p.s. attached Sci. Am article (just appeared on the newstands) much better than the WSJ...
At 10:58 AM 2/14/2005, Tom Wigley wrote:
Mike,
I'm sorry we had no time to talk at Stanford.
Here is the answer to the LIA bounce back idea ...
For 20th century warming to be a bounce back, the
heat must come from somewhere. The only source
consistent with the bounce back idea is the ocean.
The Levitus data show that heat has been going INTO
the ocean, not coming out of it.
This is really obvious, but I have never seem it stated
anywhere.
----------
Re WSJ. They say ...
"Statistician Francis Zwiers of Environment Canada, a government agency,
says he now agrees that Dr. Mann's statistical method "preferentially
produces hockey sticks when there are none in the data."
Dr. Mann, while agreeing that his mathematical method tends to find
hockey-stick shapes, says this doesn't mean its results in this case are
wrong. Indeed, Dr. Mann says he can create the same shape from the
climate data using completely different math techniques."
-----------------
It is a bit worrying that Francis agrees with M&M -- but it seems that
you do too.
My questions are:
(1) Do other reconstructions (not including Lonnie Thompson's of course)
suffer from this standardization problem?
(2) You have stated that simply averaging the data together gives the
same result. Has this elementary method been published?
(2a) I note that the PC1 amplitude time series invariably correlates highly
with the (non-areally-weighted) 'area average'. So this brings up the issue
of whether you use some area weighting in your PCA -- as we
invariably do when doing PCA of gridded data?
(3) From what I can see without reading their full GRL paper,
M&M think that the RE statistic has an odd sampling distribution.
It is easy to show this by Monte Carlo simulation -- have you done
this (i.e., in the abstract, as a statistical exercise, not for the specific
case of MBH98, etc.)?
Tom.
______________________________________________________________
Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
_______________________________________________________________________
e-mail: mann@virginia.edu Phone: (434) 924-7770 FAX: (434) 982-2137
[1]http://www.evsc.virginia.edu/faculty/people/mann.shtml
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