Subject: thoughts and Figure for MWP box
Date: Mon Jul 18 17:12:06 2005
Dear Peck, Eystein and Tom
At this point we thought it was important to review where we think we are with the MWP
First, we have no objection to a Figure . Our only concerns have been that we should
1/... be clear what we wish this Figure to illustrate (in the specific context of the MWP
box) - note that this is very different from trying to produce a Figure in such a way as to
bias what it says (I am not suggesting that we are, but we have to guard against any later
charge that we did this). We say this because there are intonations in some of Peck's
previous messages that he wishes to "nail" the MWP - i.e. this could be interpreted as
trying to say there was no such thing, and
2/ ...agree that we have done this in the best way.
The truth is that there IS a period of relative warmth around the end of the 1st and start
of the 2nd millennium C.E. , but that there are much fewer data to base this conclusion on
(and hence the uncertainty around even our multiple calibrated multi-proxy reconstructions
are wide). The geographical spread of data also impart a northern (and land) bias in our
early proxy data. My understanding of Tom's rationale with the Figure is that we should
show how, because the timing of maximum pre-20th century warmth is different in different
records, the magnitude of the warmest period (for the Hemisphere , or globe, as a whole) is
less than the recently observed warmth.
The reconstructions we plot in Chapter 6 already express the mean Hemispheric warmth (after
various selection and scaling of data), and so the additional information that the MWP box
figure should show must relate to the scatter of the proxy data. There seems to be a
consensus that this is best done by showing individual records , and we are happy to agree.
What we worry very much about, however, is that we should not produce a Figure that then
conflicts with the picture of proxy evidence for Hemispheric mean warmth as a whole,shown
in the main Chapter Figure. By showing a composite (as Tom has done) and scaling against
another (30-90degrees N) temperature record - this is just what is done.
As we promised, Tim has produced a similar Figure, using the same series plus a few extras,
but omitting the composite mean and the scaling against instrumental temperatures. The idea
was to include as many of the original input series (to the various reconstructions) as we
could - though avoiding conflicting use of different versions of the same data. The
precise selection of records will have to be agreed and, presumably, based on some clear,
objective criteria that we would need to justify (this will not be straight forward). This,
along with Tom's plot (forwarded by Peck) is in the attachment.
We would like to get your opinion now, and especially Tom's, on the points regarding the
composite and scaling. We would be in favour of just showing the series - but do they make
the point (and emphasise the message of the text in the box)? Or does the scatter of the
various series as plotted, dilute the message about the strength of 20th century mean
warming (note the apparently greater scatter in the 20th century in our figure than in
Tom's)? Can you all chip in here please.
Keith and Tim
P.S. We agreed in Beijing that we should definitely ask Tom to be a CA .
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.