date: Wed Mar 16 16:57:46 2005
from: Keith Briffa <k.briffaatXYZxyz.ac.uk>
subject: Re: last millennium - responding to Susan
to: Jonathan Overpeck <jtoatXYZxyzrizona.edu>
I am slowly getting teaching duties behind me and certainly turning my attention back to
IPCC. I have spoken wit Phil re the observations chapter and we have discussed the need to
show pre 20th instrumental data in our chapter in a manner that is relevant to the
comparison with more recent instrumental (ie N.Hemisphere or global mean) records , and the
possibility of showing ensembles of regional temperature records , and composites in a way
that possibly bares on the discussions with Susan. We are still considering this question ,
but certainly there needs to be some "frozen grid" curves as flagged in the ZOD.
I am not sure of the context of the discussion you are having with Susan , or the logic for
what Tom Crowley is trying to do with the ensemble curves of various palaeo-series.
I flagged clearly at the outset that I would like to do some regional comparisons of
various data/reconstructions . This required more time and input than was achievable for
the ZOD. I still think this is desirable though. Similarly , there is far too little in the
current version about moisture variability in the last 2000 years and too little on the
S.Hemisphere in general. It was always clear that there would be much more discussion on
the scaling issue and specific reference to work that will explore the effect of regional,
seasonal and methodological differences in aggregation and scaling (including timescale
dependent effects). The problem is that the work on much of this is not yet done or
published. It should be immediately apparent that our greatest enemy , acting against a
thorough exposition of these issues , is the lack of sufficient allotted space.
Now , returning to the Crowley Figures , I do not see how not showing an integrated and
"appropriately" scaled record helps to clarify the picture on the precedence of recent
warming in any clear way. On the contrary , it merely confuses the issue by omitting to
tackle the knotty problem of expressing an underlying mean large-scale signal , that
emerges from the regional noise only through aggregation of demonstrably appropriate
palaeo-records . This aggregation should allow quantification (with appropriate
uncertainty) of the extent of warming and provide clearly defined target for comparison
with model simulations.
If it thought appropriate , yes we can show individual records , but just normalising them
over a common base ignores the different sensitivities and regional distribution issues .
I am not convinced this selective presentation clarifies anything. I would be happy for
this discussion to opened to the rest of the author team.
At 16:28 15/03/2005, you wrote:
Hi Keith - I can't remember when you said you'd be able to get back into the IPCC fray,
but I hope it is soon. Please let me and Eystein know what you think regarding the email
I just cc'd to you. We should respond to Susan asap. Hope things are going well. Thanks,
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
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fax: +1 520 792-8795
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.