Thursday, March 15, 2012


cc: Chris Miller <>,,,,,,
date: Mon, 03 Feb 2003 14:16:20 -0500
from: "Michael E. Mann" <>
subject: Re: [Fwd: tree rings and late 20th century warming]
to: Jeff Severinghaus <>, Phil Jones <>, Thomas R Karl <>, Ray Bradley <>

Choice of aligning has no influence on the slope of the curve, it simply changes the mean
baseline for comparison. The Mann et al reconstruction has the same amplitude increase as
the full Northern Hemisphere annual mean instrumental record over the calibration interval
(1900-1980). On this simple point, there is no debate. And this seems to be the origin of
your misunderstanding of the issues involved.
Briffa & Osborn use a slightly different convention from that used elsewhere (e.g. IPCC and
in the attached Science piece which I've re-sent for the benefit of your expanded recipient
list), and by their convention the instrumental record is observed to lie ever-so-slightly
above the MBH reconstruction over the entire interval available for comparison (mid 19th
century-> 1980). This difference is actually quite small, so I'm not sure why we're even
discussing it in the first place. It, however, does not in any case impact a comparison of
the trends in the two series, which match remarkably well over that same interval. This is
despite the fact that the MBH reconstruction represents the entire Northern Hemisphere
(which gets half of its contribution from the tropics i.e., latitudes < 30N) while the
instrumental series shown by Briffa & Osborn is only the extratropics north of 20N.
This is old stuff, and I would guess that the others cc'd in on this message (Ray,
Malcolm, Keith, Phil) are not interested in re-hashing these old discussions. The state of
the the science here has moved well beyond these semantic and/or conventional arguments,
focusing instead on detailed intercomparisons of methods and data (employing rigorous
diagnostics of reconstructive fidelity (collaborative between
Bradley/Briffa/Hughes/Jones/Mann/Osborn/Rutherford). There is little disagreement between
us on the broad trends when seasonal and spatial sampling issues, and differing conventions
for e.g. defining reference periods, have been taken appropriately into account.
I hope you find that the above information clarifying Jeff. Due to other demands on my
time, I have to sign out now on this series of exchanges.
best regards,
Mike Mann
At 09:55 AM 2/3/03 -0800, Jeff Severinghaus wrote:

Please accept my apologies if I have gotten the story wrong. I am not a specialist in
the tree-ring field, and was simply reporting what I saw in the Briffa and Osborne
paper, several other papers, and what several tree-ring people have told me in
conversations. I agree, we need to keep the level of misinformation out there down to a
minimum! I regret adding to it.
I am still confused, however, about Mike's explanation for the Briffa and Osborne
paper's curve appearing flat after 1950 AD. Can you try explaining this again, Mike,
please? I don't understand how aligning could change the slope of a curve. The curves
appear to continue to 1990 AD or so, and the Esper et al. curve continues to 1993. So
the explanation that the records only go up to 1980 doesn't seem to hold in this case.
The dashed black line is the instrumental record for warm-season >20 N latitudes and it
does indeed diverge from the tree-ring records in the 1980s. Can you help me out here?
At 4:36 PM +0000 2/3/03, Phil Jones wrote:

Mike's answer is a fair response. Jeff has mixed some facts up and this is maybe
because we've never explained them clearly enough. There are two facts:
1. There are few tree-core series that extend beyond the early 1980s. This is because
many of the sites we're using were cored before the early 1980s. So most tree-ring
just don't exist post 1980.
2. The majority of the recent warming is post-1980, so no proxy would pick this up.
This warming has been large and it would be good to go back and see if the trees have
picked it up. It would give more faith in tree-ring reconstructions, but any
method is being pushed to the limit by the rate of temperature rise over the late 20th
century. Applies to other proxies but you have to note the following:
It is important to remember that locally few regions exhibit statistically
warming. Highly significant at the hemispheric level, but not great at the local level
due to high level's of variability. The spatial scales are important and this is
difficult to
get across.
At 09:15 03/02/03 -0500, Michael E. Mann wrote:

Dear Tom,
Have no fear, Jeff has still got his facts wrong, even after going back and checking
First off, I never made any such comment to Jeff--he clearly misunderstood comments that
I made at EGS a year ago in response to a question he asked. Of course, it is well know
that there are a number of competing explanations [this is what I said--to quote this as
offering "no explanation" is a bit unfair Jeff, don't you think? As I recall, I even
invited Tim Osborn in the audience to add his own comments--but he had little to say]
for the fact that *high latitude*, primarily *summer responsive*, tree-ring *density*
data have exhibited a noteable decline in the past few decades in the amplitude of their
response to temperature variability. We have discussed this issue time and again in our
own work, and Keith Briffa, Malcolm Hughes, and many others have published on this, w/
competing possible explanations (stratospheric ozone changes, incidentally, is the least
plausible to me of multiple competing, more plausible explanations that have been
published). See e.g.:
Vaganov, E.A., M.K. Hughes, A.V. Kirdyanov, F.H. Schweingruber, and P.P. Silkin,
Influence of Snowfall and Melt Timing on Tree Growth in Subarctic Eurasia, Nature, 400
(July 8), 149-151, 1999.
It should *also* be noted that we used essentially none of these data in the multiproxy
Mann/Bradley/Hughes (MBH) reconstruction, and that the MBH reconstruction tracks the
instrumental record quite well through the very end of our calibration interval
(1980--it stops then because there are far fewer paleo records available after 1980).
This was shown in our 1998 Nature article quite clearly, and of course remains true
today. Jeff made the mistake of only looking at the Briffa & Osborn paper, which doesn't
properly align the 20th century means of the various reconstructions and instrumental
An appropriate alignment of all the records is provided in IPCC, and in the attached
Science perspective from last year. This shows how well the Mann et al reconstruction
(and several model-based estimates) track the entire instrumental record. There are some
good reasons that some of the other purely tree-ring based reconstructions differ in
their details, in addition to the greater influence of the recent high-latitude density
decline issue, and these are discussed in IPCC and the Science piece. Of course, we have
in, our own work provided detailed calibration and verification statistics that
establish the skill in our reconsruction in capturing the details of both the modern
instrumental record, and independent, withheld earlier instrumental data (19th century
and, more sparsely, 18th century), and we publish uncertainties that are based on
rigorous analysis of the calibration and cross-validation residuals. I know that Jeff
has seen me talk on this many times, and probably has read our work (I would hope), so
I'm frankly a bit disappointed at the comments. I would have liked to think that he
would have approached us first, before broadcasting a message full of factual errors.
Please let me, or any of the others know, if we can provide any further information that
would help to clarify (rather than obscure!) the facts,
At 07:49 AM 2/3/2003 -0500, Thomas R Karl wrote:

Correct me if I am wrong, but I always thought the failure was a lack of tree cores
subsequent to the 1980s. Please correct me if I am wrong, and if Jeff is correct, then
indeed we have a significant implication.
-------- Original Message --------
Subject: tree rings and late 20th century warming
Date: Sun, 2 Feb 2003 16:15:04 -0800
From: Jeff Severinghaus <[1]><>
To: <[2]>
Dear Dr. Karl,
I enjoyed your presentation yesterday at the MIT Global Change forum. You
may recall that I asked about the failure of tree rings to record the 20th
century warming. Now that I look at my records, I realize that I
remembered this wrongly: it is the LATE 20th century warming that the tree
rings fail to record, and indeed, they do record the early 20th century
If you look at the figure in the attached article in Science by Briffa and
Osborn, you will note that tree-ring temperature reconstructions are flat
from 1950 onward. I asked Mike Mann about this discrepancy at a meeting
recently, and he said he didn't have an explanation. It sounded like it is
an embarrassment to the tree ring community that their indicator does not
seem to be responding to the pronounced warming of the past 50 years. Ed
Cook of the Lamont Tree-Ring Lab tells me that there is some speculation
that stratospheric ozone depletion may have affected the trees, in which
case the pre-1950 record is OK. But alternatively, he says it is possible
that the trees have exceeded the linear part of their temperature-sensitive
range, and they no longer are stimulated by temperature. In this case
there is trouble for the paleo record. Kieth Briffa first documented this
late 20th century loss of response.
Personally, I think that the tree ring records should be able to reproduce
the instrumental record, as a first test of the validity of this proxy. To
me it casts doubt on the integrity of this proxy that it fails this test.
copies to Ray Weiss, Wally Broecker
Jeff Severinghaus
Associate Professor of Geosciences
Scripps Institution of Oceanography
University of California, San Diego 92093-0244
(858) 822-2483 voice
(858) 822-3310 fax
Address for Fedex deliveries:
Rm 211 Vaughan Hall
8675 Discovery Way
La Jolla, CA 92037

Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
e-mail: Phone: (434) 924-7770 FAX: (434) 982-2137


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

Jeff Severinghaus
Associate Professor of Geosciences
Scripps Institution of Oceanography
University of California, San Diego 92093-0244
(858) 822-2483 voice
(858) 822-3310 fax
Address for Fedex deliveries:
Rm 211 Vaughan Hall
8675 Discovery Way
La Jolla, CA 92037

Professor Michael E. Mann
Department of Environmental Sciences, Clark Hall
University of Virginia
Charlottesville, VA 22903
e-mail: Phone: (434) 924-7770 FAX: (434) 982-2137
Attachment Converted: "c:\eudora\attach\MannPersp2002.pdf"

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