Friday, May 11, 2012


date: Mon, 28 Apr 2003 14:46:11 +0100
from: Phil Jones <>
subject: Fwd: Re: Fwd: RE: Rog Outline

Somewhere in this message is Mike's review of the seasonal cycle paper.

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Date: Mon, 28 Apr 2003 09:02:43 -0400
To: Phil Jones <>
From: "Michael E. Mann" <>
Subject: Re: Fwd: RE: Rog Outline
HI Phil,
Re, DeFreitas--good to hear. That piece that Jim Salinger just forwarded is especially
Thanks for the message. I just got the record from Cronin before your email, so we're in
pretty good shape. It would be nice if we can get the Briffa/Obsborn, Cook, and D'Arrigo
et al series, but already we can do a reasaonble 2K composite. I've mostly been trying
to seek out the long (2K) series so we can do the longer composite, but I suppose it
would be useful to show a few key new records (especially tropical ones) that are
I'm also working on filling in some details and preparing rought drafts of the various
sections, so perhaps within a week we can merge what we have...
Review on the JGR paper appended below. As you might imagine, my main sensitivity was w/
conclusions about implications for e.g. Mann et al which I didn't think necessarily
followed from this analysis. The revisions requested are mostly changes in wording, and
it should be straightforward to address them in a final version...
General Comments:
This is an interesting manuscript, raising some important issues regarding seasonality
of past temperature trends that are interesting in there own right, and may have
potential implications for certain paleoclimate reconstructions. These issues are worthy
of discussion in the literature, and JGR is an appropriate venue. The authors, as is
typical, have done a careful job with their analysis, and it appears sound, as do the
primary conclusions, although I have some specific reservations. The primary criticism
is that the authors imply a greater generality to their conclusions than can actually be
justified, given the limitations of the available data series. There are a number of
important caveats that need to be invoked in the interpretation of the results, and the
limitations in drawing large-scale conclusions from the limited data need to be
acknowledged up front. There are a number of underlying issues regarding the nature of
the seasonal and spatial details of past climate change (in particular, forced climate
change) which likely impact the interpretation of the results, which are not given
adequate discussion in the manuscript at present. Given the space available in a JGR
paper (vs. e.g. a GRL article), there is no excuse for not providing more detailed
discussion where appropriate. I provide several specific comments below along these
lines which should be addressed in a revised version of the manuscript.
Specific Comments
1) Abstract--the generality of the conclusions are overstated in the abstract. The
evidence is only from Europe and China (i.e, only the fringes of the Eurasian continent
alone) but the wording argues that implications apply to other regions. It isn't even
clear that the conclusions apply to the interior of the Eurasian continent, let alone
any of North America (see comments below). It is a leap of faith, then, to assume that
the results generalize to extratropical hemispheric (let alone, full hemispheric)
trends, and the authors need to be more cautious in drawing general conclusions.
2) Introduction, first sentence: There is a potential "straw man" argument being
introduced here. Precisely which "annual temperature" reconstructions are being referred
to here? The statement made could arguably apply to Crowley and Lowery (2000), which is
based on scaling a composite of largely extratropical (and mostly summer-sensitive)
proxy records against the annual mean Northern Hemisphere mean instrumental series. It
is far more difficult, however, to argue that the authors' statements fairly
characterize the Mann et al (1998;1999) annual mean temperature reconstruction. In the
latter case, half of the area of the hemispheric mean surface temperature reconstruction
comes from tropical latitudes (i.e., latitudes below 30N), and the proxy indicators
primarily used to calibrate the tropical annual-mean patterns of variance are almost
certainly not boreal warm-season in nature (for the example, the ENSO-scale patterns of
tropical SST variance in the reconstruction are calibrated, in large part, by a
combination of cold-season drought sensitive tree-ring data from Mexico, tropical
tree-ring data, and tropical corals and ice cores--none of which could be argued to
exhibit a boreal warm-season sensitivity bias!). The authors arguments cannot be argued
to apply to these reconstructions (as seems to be implied by later comments--see below).
3) Discussion of Figures 1 and 2 on pages 5-6: the authors should compare a single
long-term composite series based on averaging the various (potentially, standardized)
station JJA-DJF series with that which is available for the full NH back through the mid
19th century. The point here is to see how well they compare in terms of the general
trends during the interval (back through the mid 19th century) of overlap--in fact,
based on inspection of e.g. Figure 1, I don't think that there will be much similarity,
and, if that is the case, then it demands extreme caution in generalizing about the true
large-scale or hemispheric nature of inferred trends in summer-winter temperature
differences based on the sparse long series available to the authors.
4) Related to point #3 above, recent studies (see e.g. the discussion in the Mann, 2002
piece which is in the reference list but not actually cited in the text, and also the
results of Shindell et al, 2003) have shown that large seasonal differences in
temperature trends are expected in past centuries because of the seasonally-specific
response, in particular, to volcanic forcing (see Kirchner et al, 1999). The largest
seasonal differences are likely to occur in the continental centers, where volcanic
forcing tends to impart a large summer cooling but also typically a sizeable
dynamically-induced warming (related to the response of the Northern Annual Mode, or
'AO' or 'NAO' to volcanic stratospheric aerosol forcing) in the following winter The
large differences, however, are observed over the continental centers, and in fringe
regions such as Europe or China, the response may not even be of the same sign as the
continental mean response, which is dominated by the behavior of the continental
centers. Thus, any spatial network (proxy or instrumental) which exhibits a bias with
respect to the sampling of the continents is likely to exhibit a bias in terms of the
estimate of summer-winter temperature differences (Mann, 2002). Since the authors
instrumental network only samples the fringes of the Eurasian continent, it is very
unlikely to capture the true winter-summer difference in Eurasian continental mean
temperature, let alone Northern Hemisphere extratropical continental (Eurasia and North
America) temperature, let alone Northern Hemisphere extratropical mean (land and ocean)
temperature, let alone true Northern Hemisphere (tropical and extratropical, land and
ocean) temperature! Once again, this calls for caveats in the interpretation of the
present results with regard to hemisphere-scale implications.
5) Related to the above, why don't the authors show, in Figure 1, the results for some
of the long available North American series (which includes several long east coast
series, but also a series in Minnesota back to the early 19th century) to establish the
similarity of the longer-term summer-winter trends in the two continents (this too
should be included in the composite discussed in point #3 above).
6) End of first paragraph on page 6, the authors might note that certain modeling
studies (Shindell et al, 2003) have indeed already looked at potential
seasonally-distinct temperature changes in past centuries, that are associated with the
seasonally-distinct signature of the response to known natural climate forcings.
7) Figure 3 indicates a relationship that holds during the latter 20th century,
presumably somewhat specific to the mix of internal and forced variability that
dominates over that period. This may not be representative of the situation in earlier
centuries, where the primary pattern of forced variability is by volcanic and solar
forcing which impart distinct regional and seasonal signatures in the temperature field
(see Shindell et al, 2001;2003) that are likely to be quite different from those
associated with anthropogenic forcing (GHG and aerosol) which dominate during the
interval examined by the authors. Related to this, have the series been detrended before
calculating the correlations shown in Figure 3? This has a bearing on the
8) 3rd paragraph on page 7, the discussion of previous work (e.g. Mann et al, 1998;1999)
here is misleading for the reasons spelled out in point #2 above. The arguments
assuming a warm-season sensitivity bias do not apply to the full hemispheric
reconstruction but, at most, the extratropical component of the reconstruction. The
statement (2 sentences up from bottom of paragraph) "Their implicit assumption that the
relative trends..." is not a fair statement in reference to the Mann et al multiproxy
reconstructions, and the discussion needs to be revised here. An analysis (Rutherford et
al, to be submitted) shows, using a common statistical method, but distinct data sets,
that the multiproxy network of Mann et al calibrates and cross-validates cold-season
variability more skillfully than the tree-ring maximum latewood density ('MXD') density
network of Briffa and coworkers, while the Briffa et al MXD network, in turn, calibrates
warm-season variance more skillfully than the multiproxy network. In short, the
conclusions drawn here don't apply to reconstructions of tropical surface temperature
variability, nor to multiproxy data used to reconstruct that variability, so the
implications of the authors results for multiproxy reconstructions of full Northern
Hemisphere annual mean temperature are not clear. The authors need to downplay their
conclusions in this regard.
9) The authors and this reviewer are in common agreement that seasonally-specific
biases are likely to be present in most climate proxy data, and that these biases need
to closely considered in the process of climate reconstruction. This is a fair point,
and one worth emphasizing in the conclusions But the specific conclusions of the authors
in this study regarding summer-winter differences based on the series analyzed do not
clearly generalize to other proxy-based surface temperature reconstructions
(particularly multiproxy reconstructions with an equal tropical and extratropical
emphasis) for the reasons spelled out above, and this point, in fairness, should be
Kirchner, I., G.L. Stenchikov, H.-F. Graf, A. Robock, and J.C. Antuna, Climate model
simulation of winter warming and summer cooling following the 1991 Mount Pinatubo
volcanic eruption, Journal of Geophysical Research, 104 (D16), 19039-19055, 1999.
Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar forcing of
regional climate change during the Maunder Minimum, Science, 294, 2149-2152, 2001.
Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of
"Little Ice Age" Surface Temperature Changes, Journal of Climate, in press, 2003.
At 01:44 PM 4/28/2003 +0100, you wrote:

Now had a chance to catch up a little. On de Freitas I hope something is going to
but I don't to say anything yet. Hans and Clare will write to the publishers and try to
the reviews from de Freitas. Hans is now convinced he should go, but wants to do on a
cause basis and by the book so any backlash can be dealt with in a fair manner.
I think I might have mentioned this to you in an email from Duke, but I must have
something wrong as I've lost some emails. I can't find the one from you saying you'd
the recent JGR paper on the annual cycle, for example. I was bleary eyed at times at
but I'm sure I read it ! Can you send the review if it's easy to locate ?
On RoG all the series you've mentioned would be good to get. Tim is away here so I
can't ask him if he's sent the Eurasian one, but I'll check when he's here. All the
seem good ones to go for. I'll email Dahl-Jenssen to see if I can get anything.
As for the title, why don't we go for 'Climate during the past two millennia',
still with the
empahsis on the last one. This way it won't be too different from the one we gave to
The first millennia will be semi quantitative and would just be smoothed versions -
averages of what we can get, scaled against NH extended summers. We should probably
put less emphasis on the MWP as Ray/Henry/Malcolm are working on that and more on
the LIA in discussion - thinking aloud here. We could ask Ray for a draft in a couple
months and exchange bits of text. I did think of Climate during the Christian Era !!!
but that
was going too far ! So, we will use AD and BC dates if needed, remembering AD goes
At the EGS there was a 300 year coral series from Malindi, Kenya from Rob Dunbar
we should get. I'll email Rob if I can find his email address.
Finally, I've written two sections on instrumental and documentary for section 2.
someone to type these in here and I'll work on them a bit before sending. I need to get
Astrid's views on a few sentences on the Norse. Also I'll start a reference list as
this might
be a good way to start - who we must reference and also acknowledge. When I began the
writing I realised it wouldn't take too long as there isn't that much space. So
Figures, Refs,
Captions, Acknowledgements are crucial.
Ed also has some Nepalese reconstructions - he's just got a paper in proof stage.
are not that long though, late 1500s. When he comes through you could ask him for those
At 16:59 26/04/03 -0400, you wrote:

Hi Phil,
I've managed to get my hands on the long chinese reconstruction, and have sent out
requests for data to Ed Cook (the long RCS series from Esper et al), Tim (their long
Eurasian reconstruction as published in the '99 Science piece--haven't hear from Tim
yet, can you look into this?), D'Arrigo/Jacoby (Sol Dav Mongolia record) , and Cronin
(Chesapeake Bay spring temperature reconstruction). Ray apparently has been trying to
get the Dye3/GRIP borehole data from Dahl-Jensen for some time, but without
success--perhaps you could also try to get ahold of these?
I'm going to make a preliminary attempt based on the few long (2K) records I already
have (western U.S., China, Quelccaya o18, Fennoscandia) to use as a placeholder in the
paper if nothing else, and we can improve on this as we get more data. Since we'll
probably only want to form a composite at decadal resolution, we can probably scan many
of the records if we haven't received them (I'm supporting an undergrad on a grant who,
among other things, will be able to scan in series for us--they start in less than a
let me know what you think. thanks,

Date: Thu, 24 Apr 2003 13:59:28 -0400
From: "Michael E. Mann" <>
Subject: Fwd: RE: Rog Outline
Can I get from you the Eurasian composite that you and Keith published in the Science
perspective in '99? Phil and I are working on trying to do a simple-minded composite of
a few of the 2K length temperature proxies for a piece we're working on together.
thanks in advance for any help you can provide,

Date: Thu, 24 Apr 2003 11:14:26 +0100
Sender: f028 <>
From: f028 <>
To: "Michael E. Mann" <>
X-EXP32-SerialNo: 00104935
Subject: RE: Rog Outline
X-Mailer: InterChange (Hydra) SMTP v3.61.08
Let's try and do this. I'll get back to you with more ideas next week.
So for the moment, let's go with the last few or two millennia. I'll
talk to a few who are here at Duke.
Send revisions then assuming last few millennia, but the main emphasis
will still be the last one.

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

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

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

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