Saturday, June 2, 2012


cc: Jens Hesselbjerg Christensen <>, Eigil Kaas <>
date: Fri, 07 Jan 2005 14:51:53 +0100
from: Martin Stendel <>
subject: [Fwd: Mike Mann's claims]
to: Hans von Storch <>, Eduardo Zorita <>, Keith Briffa <>

Dear Hans,
sorry for the late reply. I was involved with finishing up the final report of a recently
finished EU project.
The problem we are facing here is the reconstruction of climate variability on a
multicentury time scale from a calibration period of about 100 years. There is therefore
only limited possibility to directly compare the Mann reconstructions (for the "real
world") and the von Storch results (in the "model world").
We do not know the transfer function which projects the proxies on the temperature (but we
will likely underestimate the low frequency contribution for methodical reasons). However,
the proxies themselves are not directly comparable as well, since in the "real world" they
always are an integral over some climate variation, while the pseudoproxies in the model
are not. Even if they were, we could not anticipate they have the same temporal behaviour.
Furthermore, it is required that the climate in the calibration period does not differ
significantly from that of the reconstruction period. Since there were no major volcanic
eruptions in the 20th century (of the order of Tambora), it is not clear if this assumption
holds, and it is thus likely that we underestimate these effects in any reconstruction. It
is not clear to me whether this effect will be the same in the real world and in the model
(and how large it is).
The von Storch simulations and our results can as well not be compared with each other in a
straightforward way. The model we have used in our simulation is similar but not identical
to the model von Storch's group has used:
* The atmospheric model is the same, however we have used a higher resolution (T42
compared to T30 in the GKSS simulation). A direct comparison of these two models has
been conducted in the EU project GLIMPSE. While both models are able to depict the
general temperature trends ("Little Ice Age", 20th century warming etc.), we find
differences in detail. Most striking, our simulation shows a considerably more blocking
situations over Western Europe during cold periods (LMM and early 19th century) than
the T30 GKSS version in spite of a much smaller forcing (see below).

* The ocean models are different. We have used the OPYC model, whereas the von Storch
group used the HOPE model.

* There are considerable differences in forcing between the two simulations. Apart from
the often mentioned magnitude of the solar and volcanic forcing (our forcings being
considerably smaller), our volcanic forcing has a latitudinal dependence and takes into
account both short-wave and long-wave effects, although only in a simplified form. This
results in comparably large negative forcings in our experiment for large extratropical
eruptions. Furthermore, we take into account the contribution of vegetation changes.
Although globally small, this effect cannot be neglected regionally.

In the paper we have submitted to Climate Dynamics we show that our low frequency
variability lies in between the Mann curve and the von Storch simulation. Given all the
differences mentioned above, it is difficult to make a more quantitative assessment. An
answer to the question would e.g. require to redo the von Storch analysis with our data and
compare these two results.
Hans, I already sent you a copy of the manuscript. There was, however, an error in Fig. 2.
The Mann data Irene downloaded from the official WCD-P page were already smoothed, but this
was not mentioned in the readme text (but has been corrected now). When she smoothed the
data sets in Fig. 2, she therefore applied the smoothing twice. The effect is not very
large and does not change our statements, but it is visible. I attach the corrected file.
I don't have any other papers on this issue in the pipeline, and I am not reviewing the
papers Keith mentioned.
I agree that this issue urgently needs further clarification given the potential political
implications. Please keep us updated!
Best regards from Copenhagen, also on behalf of Eigil and Jens
-------- Original-Nachricht --------

Betreff: Mike Mann's claims
Datum: Tue, 04 Jan 2005 19:34:24 +0100
Von: [1]
An: [2], [3]
CC: [4], [5]

Dear Martin, dear Keith,
Mike Mann has made the following claims:
"You should be aware that a comment is in press in "Science" casting significant doubt on
the claims of Von Storch and Zorita, and another paper, in review, suggests that their
conclusions are incorrect, . A 3rd paper, by the Danish Meteorological Institute (DMI)
group using the same model as von Storch, cannot reproduce the von Stroch results (they
find much less variability than von Storch), suggesting that their were some serious
problems with the von Storch simulation as well as with their analysis of the simulation
results. I would suggest that you get in touch with these individuals (e.g. Keith Briffa:
[6] or Martin Stendel: [7] for a more balanced view of the Von
Storch claims."
May I ask you to verify this statement and, if true, send us a copy of your papers? And,
possibly, explain your "more balanced views"?
All the best
Hans von Storch
Institute for Coastal Research, GKSS Research Center
Max-Planck-Strasse 1, 21502 GEESTHACHT, Germany
ph: +49 4152 87 1831, fx: +49 4152 87 2832
mobile: + 49 171 212 2046
[8]; [9]
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