Friday, May 18, 2012


cc: "Olga Solomina" <>, Eystein Jansen <>,, Valerie Masson-Delmotte <>, "Ricardo Villalba" <>
date: Thu, 6 Jan 2005 17:02:37 -0700
from: Jonathan Overpeck <>
subject: Re: Fwd: Re: Fwd: Re: [Wg1-ar4-ch06] IPCC last 2000 years data
to: Keith Briffa <>

Thanks Keith. Eystein and I just discussed this all again and we have a proposed plan for

Olga (and others - please note!) - we're running into serious space problems and are
making lots of hard cuts all over the chapter. We'd therefore suggest reducing the glacier
discussion in sections and to a mimimum, and a level required by those
sections (Keith and Valerie decide for now). We then want to take out and condense that
information that is focused on one very important aspect of the glacier story. We propose
to put this in a new cross-cutting box (label it Box 6.1: Long-term perspective on recent
global glacier retreat).

Given that chapter 4 will have everything regarding the recent (instrumental) record of
glacier mass balance, and the fact that many readers will be thinking - "well glaciers
melted in the past for purely natural reasons, didn't they," we want to highlight with just
a couple (2-3 paragraphs and a compelling figure) that we can put the current near-global
glacier retreat into a long-term perspective (the figure should show long records from many
sites, some going back well into the Holocene - can we do that?) , and that we can explain
why (e.g., due to orbital forcing) the glaciers melted in the past. We can also (can we?)
show that the current globally synchronous retreat cannot be explained by the same natural
forcing. The current retreat must therefore be due to some other cause (e.g., human driven
global warming). That's my take, but the data/records must speak for themselves - we can't
be biased in any way.

Of course, we need a brief intro that says why the issue is important, and how glaciers
respond to climate. David Rind provided this ref, but we know there are others:

: Greene et al. (GRL, 26, 1909-1912, 1999) did an analysis of 52 glaciated areas from
30-60N and found that the highest correlation between their ELA variations in the last 40
years was with summer season freezing height and winter season precip. The warm season
freezing height was by far more important.

Olga - does this make sense, and can you take charge of this? We think we can get Lonnie
Thompson and Ellen Mosley Thompson to help with tropical, and Atle Nesje to help with
high-latitude. Given the importance of this issue, they should at least help (review/edit),
but if we don't hear from you, we'll ask them to try for the first draft - time is very
short, and they can be CAs. We worry you might not be on-line right now, but your already
contributed prose can serve as a good start.

We don't need a fig unless we can generate a good one. But it would be very nice! What do
you think?

Please let us know what you think (Olga especially, but we want to make sure that Keith and
Valerie are ok with this - it will give you more room, although some of the space will
still come out of your sections).

Thanks, Peck and Eystein.

am sending this to get you in this loop re the discussion for slimming down the 2000
year section Basically , IN THIS BIT - the decision is to reduce the glacier evidence to
a very much smaller piece , coached in the sense of how the glacier evidence is
problematic for interpreting precise and quantitative indications of the extent of
regional or Hemispheric Warmth (and even cold) - issues of translating tongue position
or volume into specific temperature and precipitation forcing . Hence , I am having to
remove the stuff you sent and am asking if you could consider trying to write a brief
section dealing with the issues I raise ? I also attach some initial comments by David
Rind (on the full first draft of the chapter sent round by Eystein) for consideration
Sorry about this - but presumable (as you suggested earlier) some of this can go in the
10K bit. You can shout at me (and the others) later!
Hi Keith - Happy new year. Hopefully, you had a good holiday. I've had a chance to read
your section and hopefully you've had a chance to read what I sent just before the
holidays. The purpose of this email is to help get a focus on the finish line (just a
few days away) and to get a dialog going that will hopefully help you finish section If you'd like to talk on the phone, just let me know.

Please see my email from right before xmas holidays for original comments. Plus, here
are the new ones from both me and David Rind:
0) as leader of this KEY section, we need you to take the lead integrating everything
you think should be integrated, editing and boiling it down to just ca 4 pages of final
text (e.g., 8 pages of typed text plus figs). This means cutting some material (e.g.,
forcings and simulations) and perhaps moving glacier record (MUCH boiled down) to a box.
See below.
00) note that we can also perhaps move some of the details to the appendix (although we
won't write this until after the current ZOD crunch, save an outline of what you might
want in there).
1) I like your figure ideas, with the comments:
1a) I don't think you need figure 1d - the SH recons are sketchy since not much data,
and it might be better to just discuss in a sentence or three. Any space saved is good
too. Not sure about your proposed 1e - have to see it, I guess.
1b) Figure 2 looks interesting. I'm trying to get the latest Arctic recon from Konrad
Hughen - it is quite robust and a significant multi-proxy update. Should be published in
time, though not sure thing since he's still hot on including his (our) AO recon which
is more sketchy
1c) I think we can save space and improve organization if we DO NOT include Fig 3.
However, this is open for debate - see David's comments below.
2) I agree with David's comments in general - so see them below. The prickly issue is
where to put the forcings and simulated changes. I am close to having the prose from the
radiation chapter, including the latest Lean and Co's view on solar - this will make
many of the existing simulations involving inferred past solar forcing suspect (I will
send in a day or so I hope). This means that we might be best saving space and
downplaying this work some. I'm not sure, but wanted to debate it with you. Also, Chap 9
will have simulations in spades, so we can save space by letting them do it. Also, as
David points out, we can focus on it elsewhere in our chapter more concisely - leaving
you to focus on the VERY important obs record of temp and other changes. Can you tell,
I'm still not 100% sure? I'll send another email to you and others about this in a bit.
3) Your section is too long and needs to be condensed. Thus, you need to think through
what's most important and what's less so. For example, we need to figure out how to
condense the glacier record of change. David thinks it should be a separate section that
cuts across time scales (i.e., Holocene and last 2000 years). Perhaps we should try to
make it into a box - 3 to 5 short paragraphs and a figure or two. Either way we have to
really wack it. What do you think - you and I should be on the same page with Eystein
before discussing w/ Olga perhaps. Or you can discuss with her - you're the lead on this
4) you're doing an impressive job! Lots to keep track of.
Next, here is what David has offered. Take it all with a grain of salt, but I have read
it and he has many good points. On the structural or any other points, I'm happy to
discuss on the phone, or you can just debate with him and me on email.
******* From David Rind 1/4/05 ****************
6.3 Understanding Past Climate System Change (forcing and response)
6.3.1 Introduction (0.5 pages)
6.3.2 The Current Interglacial Last 2000 years (4 pages)
Figure 1 should be of the last 2000 years, with appropriate caveats, not just since 1860
(which will undoubtedly be in other chapters).
pp. 8-18: The biggest problem with what appears here is in the handling of the greater
variability found in some reconstructions, and the whole discussion of the 'hockey
stick'. The tone is defensive, and worse, it both minimizes and avoids the problems. We
should clearly say (e.g., page 12 middle paragraph) that there are substantial
uncertainties that remain concerning the degree of variability - warming prior to 12K
BP, and cooling during the LIA, due primarily to the use of paleo-indicators of
uncertain applicability, and the lack of global (especially tropical) data. Attempting
to avoid such statements will just cause more problems.

In addition, some of the comments are probably wrong - the warm-season bias (p.12)
should if anything produce less variability, since warm seasons (at least in GCMs)
feature smaller climate changes than cold seasons. The discussion of uncertainties in
tree ring reconstructions should be direct, not referred to other references - it's
important for this document. How the long-term growth is factored in/out should be
mentioned as a prime problem. The lack of tropical data - a few corals prior to 1700 -
has got to be discussed.
The primary criticism of McIntyre and McKitrick, which has gotten a lot of play on the
Internet, is that Mann et al. transformed each tree ring prior to calculating PCs by
subtracting the 1902-1980 mean, rather than using the length of the full time series
(e.g., 1400-1980), as is generally done. M&M claim that when they used that procedure
with a red noise spectrum, it always resulted in a 'hockey stick'. Is this true? If so,
it constitutes a devastating criticism of the approach; if not, it should be refuted.
While IPCC cannot be expected to respond to every criticism a priori, this one has
gotten such publicity it would be foolhardy to avoid it.
In addition, there are other valid criticisms to the PC approach. Assuming that the PC
structure stays the same was acknowledged in the Mann et al paper as somewhat risky,
given the possibility of altered climate forcing (e.g., solar). Attempting to
reconstruct tropical temperatures using high latitude PCs assumes that the PCs are
influenced only by global scale processes. In a paper we now have in review in JGR, and
in other papers already published, it is shown that high latitude climate changes can
directly affect the local expression of the modes of variability (NAO in particular).
So attempting to fill in data at other locations from PCs that could have local
influences may not work well; at the least, it has large uncertainties associated with
The section from p.18-20 - simulations of temperature change over the last millennium ,
including regional expressions - should not be in this section. It is covered in the
modeling section (several different times), and will undoubtedly be in other chapters as
well. And the first paragraph on p. 19 is not right - only by using different forcings
have models been able to get similar responses (which does not constitute good
agreement). The discussion in the first paragraph of p. 20 is not right - the dynamic
response is almost entirely in winter, which would not have affected the 'warm season
bias' paleoreconstructions used to prove it. It also conflicts with ocean data (Gerard
Bond, personal communication). Anyway, it's part of the section that should be dropped.
pp. 20-28: The glacial variations should be summarized in a coherentglobal picture.
Variations as a function of time should be noted - not just lumped together between 1400
and 1850 - for example, it should be noted where glaciers advanced during the 17th
century and retreated during the 19th century, for that is important in understanding
possible causes for the Little Ice Age (as well as the validity of the 'hockey stick').
The discussion on the bottom of p.25-27 as to the causes of the variations is
inappropriate and should be dropped - note if solar forcing is suspect, every paragraph
that relates observed changes to solar forcing will be equally suspect (e.g., see also
p. 44, first paragraph).
Bottom of p. 27: Greene et al. (GRL, 26, 1909-1912, 1999) did an analysis of 52
glaciated areas from 30-60N and found that the highest correlation between their ELA
variations in the last 40 years was with summer season freezing height and winter season
precip. The warm season freezing height was by far more important. Therefore, the
relationship of glacier variations to NAO changes (which are important only in winter),
as discussed in this paragraph, while perhaps valid for a period of time in southern
Norway, is not generally applicable.
p. 34-36 on forcings: note that this is redundant to what is discussed in several later
sections (e.g., 6.5.2); and other chapters), and that is true of forcing in general for
the whole of section 6.2. I would strongly suggest dropping forcing from section, at least, and perhaps giving it its own number, or referring to
othersubsections for it. It has a different flavor from the responses, and the section
is already very big. Forcing does need to be discussed in the paleoclimate chapter, for
reasons of climate sensitivity and explaining observations, but that is what Chapter 6.5
is about.

(In summary - already is taking on one controversy - paleotemperatures, which is
needs to do better, It should not have to deal with the forcing problems as well, and
especially not in an off-handed way.)
Specific comments: p. 36: 6 ppm corresponds to a temperature response of 0.3 to 0.6�K
using the IPCC sensitivity range.
p. 36, last paragraph: one could equally well conclude that the reconstructions are
showing temperature changes that are too small. This is the essence of the problem with
the last 2000 years: if the reconstructions are right, either there was no solar
forcing, or climate sensitivity is very low. If the real world had more variability,
either there was solar forcing, or climate sensitivity is high (as is internal
variability). I've tried to say this in the climate sensitivity sub-chapter.
pp. 37-41: obviously a lot of overlap, but it shouldn't be hard to combine these.
p. 39, first paragraph: but can the models fully explain what is thought to have
happened? Quantification is important here, because many of the same climate/veg models
are being used to assess future changes in vegetation.
p. 42 - first full paragraph: what are the implications of the methane drop without a
CO2 drop?
p. 43, middle paragraph: obviously should mention solar-orbital forcing in this
p. 44, first paragraph: again, assuming a solar forcing
p. 45, first paragraph: overlap with pp. 20-28.
Second paragraph: overlap with p.39, last full paragraph
p. 52 - repeat of p. 43.
******* END From David Rind 1/4/05 ****************

Date: Wed, 5 Jan 2005 12:24:47 -0700
To: Keith Briffa <>
From: Jonathan Overpeck <>
Subject: Re: Fwd: Re: [Wg1-ar4-ch06] IPCC last 2000 years data
Cc: Eystein Jansen <>,,
Fortunat Joos <>, joos <>,
"Ricardo Villalba" <>
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Hi Keith and Co - I think David likes a good debates, so the main thing is to consider
his comments and respond appropriately. Although the first priority has to be on the ZOD
text and display items, maybe you can go back over his comments AFTER the looming
deadline and further discuss things with David and others. For now, just work away.
The biggest issue is how to handle forcing and simulations - i.e., where to put
different pieces in the chapter. Eystein and I will help the team work through this.
More soon, but for now just proceed as you have been proceeding. There is real merit to
the concept that your section is about how climate varied over the last 2ka, and what
caused these variations. The flip side is that we need to get a clear vision of how this
differs from what goes into the other sections. Eystein and I will work more on this
Your plan re: glaciers is good. That's a tough one, but it has to be boiled WAY down.
Moreover, my gut is to focus on the extent to which these complicated natural archives
(e.g., complicated by ppt change) support or do not support the other proxy
evidence/conclusions. This is why I was thinking we might think about a box, and to
include the Lonnie perspective in it - e.g., glaciers are now melting everywhere (almost
- we know why they are not in those places) in a manner unprecedented in the last xxxx
years. Make sense? See what Olga says, and if needbe, I can help focus that stuff more.
Thanks! Peck

Hi Peck (et al)
I am considering comments (including David's) re last 2000 years - some are valid =
some are not . Will try to chop out bits but we need this consensus re the forcing and
responses bit - I am for keeping the forcings in as much as they relate to the specific
model runs done - and results for last 1000 years as I suspect that they will not be
covered in the same way elsewhere . David makes couple good points - but extent to which
forcings different (or implementation) perhaps need addressing here. The basic agreement
I mean is that the recent warming is generally unprecedented in these simulations.

It will take time and input from the tropical ice core /coral people to do the regional
stuff well . I think the glaciological stuff is a real problem - other than just showing
recent glacial states (also covered elsewhere) - of course difficult to interpret any
past records without modelling responses (as in borehole data), but this requires
considerable space . My executive decision would be to ask Olga to try to write a couple
of papragraphs on limits of interpretation for inferring precisely timed global
temperature changes? What do others think? I only heaved Olga's stuff in at last moment
rather than not include it - but of course it needs considerable shortening. The
discussion of tree-ring stuff is problematic because it requires papers to be published
eg direct criticism of Esper et al. We surely do not want to waste space HERE going into
this esoteric topic? All points on seasonality , I agree with , but the explicit stuff
on M+M re hockey stick - where is this? ie the bit about normalisation base affecting
redness in reconstructions - sounds nonsense to me ?
I have to consider the comments in detail but am happy for hard direction re space and
focus. If concensus is no forcings and model results here fine with me - Peck and
Eystein to rule

Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth
715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
direct tel: +1 520 622-9065
fax: +1 520 792-8795

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.
Phone: +44-1603-593909
Fax: +44-1603-507784


Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth
715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
direct tel: +1 520 622-9065
fax: +1 520 792-8795

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