date: Thu, 16 Feb 2006 00:19:18 +0100
from: Eystein Jansen <Eystein.JansenatXYZxyz.uib.no>
subject: Re: Bullet debate number 1
to: Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Keith Briffa <k.briffaatXYZxyz.ac.uk>
I think we should avoid discussing the Moberg et al results in the exec. bullet. I also
think we need to have a statement about the MWP in the bullet, and I cannot really
understand why the most central conclusion from the very nice recent Osborn et al. Science
paper cannot be highlighted in the first bullet. My suggestion is:
o Some of the post-TAR studies indicate greater multi-centennial Northern Hemisphere
temperature variability than was shown in the TAR, due to the particular proxies used, and
the specific statistical methods of processing and/or scaling them to represent past
temperatures. The additional variability implies cooler temperatures, predominantly during
the 12th to 14th, the 17th, and the 19th centuries. The warmer period in the 11th century
is in general agreement with the results shown in the TAR. Consideration of the regional
records of temperature for the 11th century indicate that it is unlikely that the spatial
extent of warming during this time period was as significant as in the second half of the
At 11:46 -0700 15-02-06, Jonathan Overpeck wrote:
Hi Keith (and Eystein - we need your opinion) - thanks for the quick response. I think
it easier (imagining the mess of email that could result) if we focus on one
bullet/email. So I'll start w/ the first, and hope that Eystein can also weigh in.
With regard to the first one below, I agree that we can leave statistics out of it. Good
But, I think we must at least address Susan's concern. To do otherwise would be
counterproductive. She makes sense. I think your MWP results is quite appropriate - they
were published in Science, and in my reading of the paper, you are convincing. If it's
in the chapter, it makes sense to draw on it for the exec summary. Please defend more
convincingly, or suggest an alternative way to deal with Susan's concern - what is the
significance (not statistical) of this one record being warmer? We need to say it.
If you really want to leave as is, please write your response in a way that I can
forward to Susan - we can't ignore he comment in this case, because other (me, at least)
think it makes sense. So we have to convince her too - this is big stuff for the AR4,
and will be in the TS/SPM. We can't be as vague as the current bullet is.
And as for the MWP box fig, I think it should be as you suggest - combine the existing
fig w/ the new one from Tim and your paper. I think Tim might already be working on it?
Sorry to be a tough guy, but this bullet needs to be more clear.
do not think you will like what I say here , but I am going to give straight answers to
The new draft says enough in the text now about "far-less-accurately dated" and
"low-resolution proxy records that can not be rigorously calibrated" in relation to
this paper (Moberg et al.) . It is not appropriate to single the one series out for
specific criticism in the summary . The use of the word "only" implies we do not believe
it. Mike Mann's suggestion begs a lot of questions about what constitutes "significantly
warmer". You need to have a Null Hypothesis to test . If you mean would the estimates in
Moberg and the other reconstructions (during medieval time) show significantly different
means using a t-test - then of course not , but this tells us nothing other than they
are not likely samples from totally different populations - an almost impossible test to
pass given the wide uncertainties on all reconstructions . Incidentally, we do not have
formal (calibration ) uncertainties for Moberg anyway (just boot-strapped uncertainty on
the average low-frequency curve).
I think the vagueness is necessary - "suggests slightly" and is appropriate.
I would not call out The results of Tim and my paper either. It is just an aside in the
Medieval box at present , perhaps with a Figure to accompany the original if you agree,
but without more text in the Chapter , which I do not consider appropriate, it should
not be highlighted as a bullet.
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
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