Saturday, March 31, 2012


date: Fri, 04 Feb 2005 15:54:15 -0500
from: "Michael E. Mann" <>
subject: Fwd: Re: FW: "hockey stock" methodology misleading
to: Phil Jones <>,, tom crowley <>, tom crowley <>,,, Keith Briffa <>

Date: Fri, 04 Feb 2005 15:52:53 -0500
To: Andy Revkin <>
From: "Michael E. Mann" <>
Subject: Re: FW: "hockey stock" methodology misleading
Hi Andy,
The McIntyre and McKitrick paper is pure scientific fraud. I think you'll find this
reinforced by just about any legitimate scientist in our field you discuss this with.
Please see the RealClimate response:
and also:
The Moberg et al paper is at least real science. But there are some real problems with
it (you'll want to followup w/ people like Phil Jones for a 2nd opinion).
While the paper actually reinforces the main conclusion of previous studies (it also
finds the late 20th century to be the warmest period of the past two millennia), it
challenges various reconstructions
using tree-ring information (which includes us, but several others such as Jones et al,
Crowley, etc). I'm pretty sure, by the way, that a very similar version of the paper was
rejected previously by Science. A number of us are therefore very surprised that Nature
is publishing it, given a number of serious problems:
Their method for combining frequencies is problematic and untested:
A. they only use a handful of records, so there is a potentially large sampling bias.
B. worse, they use different records for high-frequencies and low-frequencies, so the
bias isn't even the same--the reconstruction is apples and oranges.
C. The wavelet method is problematic. We have found in our own work that you cannot
simply combine the content in different at like frequencies, because different proxies
have different signal vs. noise characteristics at different frequencies--for some
records, there century-scale variability is likely to be pure noise. They end up
therfore weighting noise as much as signal. For some of the records used, there are real
age model problems. The timescale isn't known to better than +/- a couple hundred years
in several cases. So when they average these records together, the century-scale
variability is likely to be nonsense.
D. They didn't do statistical verification. This is absolutely essential for such
reconstructions (see e.g. the recent Cook et al and Luterbacher et al papers in
Science). They should have validated their reconstruction against long-instrumental
records, as we and many others have. Without having done so, there is no reason to
believe the reconstruction has any reliability. This is a major problem w/ the paper. It
is complicated by the fact that they don't produce a pattern, but just a hemispheric
mean--that makes it difficult to do a long-term verification. But they don't attempt any
sort of verification at all! There are some decades known to be warm from the available
instrumental records (1730s, some in the 16th century) which the Moberg reconstruction
completely misses--the reconstruction gives the impression that all years are cold
between 1500 and 1750. The reconstruction would almost certainly fail cross-validation
against long instrumental records. If so, it is an unreliable estimate of past changes.
We're surprised the Nature Reviewers didn't catch this.
E. They also didn't validate their method against a model (where I believe it would
likely fail). We have done so w/ our own "hybrid frequency-domain" method that combines
information separately at low and high-frequencies, but taking into account the problem
mentioned above. This is described in:
Rutherford, S., Mann, M.E., Osborn, T.J., Bradley, R.S., Briffa, K.R., Hughes, M.K.,
Jones, P.D., [3]Proxy-based Northern Hemisphere Surface Temperature Reconstructions:
Sensitivity to Methodology, Predictor Network, Target Season and Target Domain, Journal
of Climate, in press (2005).
In work that is provisionally accepted in "Journal of Climate" (draft attached), we show
that our method gives the correct history using noisy "pseudoproxy" records derived from
a climate model simulation with large past changes in radiative forcing. Moberg et al
have not tested their method in such a manner.
F. They argue selectively for favorable comparison w/ other work:
(1) Esper et al: when authors rescaled the reconstruction using the full instrumental
record (Cook et al, 2004), they found it to be far more similar to Mann et al, Crowley
and Lowery, Jones et al, and the roughly dozen or so other empirical and model estimates
consistent w/ it. Several studies, moreover [see e.g.: Shindell, D.T., Schmidt, G.A.,
Mann, M.E., Faluvegi, G., [4]Dynamic winter climate response to large tropical volcanic
eruptions since 1600, Journal of Geophysical Research, 109, D05104, doi:
10.1029/2003JD004151, 2004.] show that extratropical, land-only summer temperatures,
which Esper et al emphasises, are likely to biased towards greater variability--so its
an apples and oranges comparison anyway.
(2) von Storch et al: There are some well known problems here: (a) their forcing is way
too large (Foukal at al in Science a couple months back indicates maybe 5 times too
large), DKMI uses same model, more conventional forcings, and get half the amplitude and
another paper submitted recently by the Belgium modeling group suggests that some severe
spin-up/initialization problems give the large century-scale swings in the model--these
are not reproducible.
(3) Boreholes: They argue that Boreholes are "physical measurements" but many papers in
the published literature have detailed the various biases in using continental ground
surface temperature to estimate past surface air temperature changes--changing snow
cover gives rise to a potentially huge bias (see e.g. : Mann, M.E., Schmidt, G.A.,
[5]Ground vs. Surface Air Temperature Trends: Implications for Borehole Surface
Temperature Reconstructions,Geophysical Research Letters, 30 (12), 1607, doi:
10.1029/2003GL017170, 2003).
Methods that try to correct for this give smaller amplitude changes from borehole
Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., [6]Optimal
Surface Temperature Reconstructions using Terrestrial Borehole Data, Journal of
Geophysical Research, 108 (D7), 4203, doi: 10.1029/2002JD002532, 2003]
[[7]Correction(Rutherford and Mann, 2004)]
Most reconstructions and model estimates still *sandwich" the Mann et al reconstruction.
See e.g. figure 5 in: Jones, P.D., Mann, M.E., [8]Climate Over Past Millennia, Reviews
of Geophysics, 42, RG2002, doi: 10.1029/2003RG000143, 2004.
Ironically, MM say our 15th century is too cold, while Moberg et al say its too warm.
To recap, I hope you don't mention MM at all. It really doesn't deserve any additional
publicity. Moberg et al is more deserving of discussion, but, as outlined above, there
are some real problems w/ it. I have reason to believe that Nature's own commentary by
Schiermeier will actually be somewhat critical of it.
I'm travelling and largely unavailable until monday. If you need to talk, you can
possibly reach me at 434-227-6969 over the weekend.
I hope this is of some help. Literally got to run now...
At 02:14 PM 2/4/2005, Andy Revkin wrote:

Hi all,
There is a fascinating paper coming in Nature next week (Moberg of Stockholm Univ., et
al) that uses mix of sediment and tree ring data to get a new view of last 2,000 years.
Very warped hockeystick shaft (centuries-scale variability very large) but still
pronounced 'unusual' 1990's blade.
i'd like your reaction/thoughts for story i'll write for next thursday's Times.
also, is there anything about the GRL paper forthcoming from Mc & Mc that warrants a
I can send you the Nature paper as pdf if you agree not to redistribute it (you know the
embargo rules).
that ok?
thanks for getting in touch!

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

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

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