cc: Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Stefan Rahmstorf <rahmstorfatXYZxyzan-klima.de>, Anders Levermann <levermannatXYZxyz-potsdam.de>, Eva Bauer <eva.baueratXYZxyz-potsdam.de>, Eystein Jansen <eystein.jansenatXYZxyz.uib.no>, Keith Briffa <k.briffaatXYZxyz.ac.uk>, email@example.com, Fortunat Joos <joosatXYZxyzmate.unibe.ch>, plattneratXYZxyzmate.unibe.ch
date: Wed, 15 Feb 2006 10:06:20 -0700
from: Jonathan Overpeck <jtoatXYZxyzrizona.edu>
subject: Re: Fwd: Re: Millennium Simulations
to: Tim Osborn <t.osbornatXYZxyz.ac.uk>
Hi Tim et al - Now that I see both (thanks Tim),
I strongly prefer 1500-1899. In addition to the
reasons spelled out by Tim, I like agree with the
point made by Tim a while back - that we're a
paleo chapter and it makes sense to see the
climate as evolving naturally until the 20th
century when anthro forcing starts to push the
system out of the natural envelop of variability.
The natural forcing only runs, just carry on as
they had for the previous 900 years. It is a
compelling way to view what the anthro forcing is
doing to the system.
Moreover, I think it would be confusing to use
one ref period for a-d, and a different one for e.
So, unless someone can really sway me and
Eystein, I say we move forward w/ the fig as
originally envisioned by Tim, but with the
suggested changes to colors and labels.
>I have redone all plots for the two alternative
>baseline periods - see attached PDF. Please
>look at them on the screen as well as printing
>them, because with some printers you can hardly
>see the paler greys and the yellow lines whereas
>they seem quite bright on my screen.
>Page 1 is 1500-1899. Page 2 is 1961-1990.
>Mine and Keith's opinion:
>1500-1899 looks better for panels (a), (c) and
>(d). They look equally as good for panel (c).
>For panel (e) we are unsure and below are some
>arguments for and against.
>[Obviously I can tidy up the 1961-1990 version a
>bit more, in terms of labelling etc., though it
>is clearly going to be tricky to find gaps for
>the key and titles and the vertical scale of
>panel (d) would need to be changed/extended a
>bit and then wouldn't match the scale I used for
>panel (e). So 1961-1990 is a bit harder to get
>everything looking good and consistent.]
>At first we thought that the new 1961-1990
>version of panel (e) looked better for the
>reason that there is clearer separation between
>the "all forcings" (thick lines) and the
>"natural-only forcings" (thin lines) in the
>early 20th century.
>On closer inspection, however, we then were
>swayed back to the 1500-1899 version of panel
>(e), because the reason for the clearer
>separation of the "Nat" and "All" runs in
>1961-1990 version is that the stronger solar
>forcing runs (dark and pale blue and green) are
>pushed downwards. But pushing them downwards
>means that during the "Little Ice Age" period
>these runs (especially the dark and pale blue
>ones) are clearly in the bottom part of the
>range of the reconstructions relative to
>1961-1990 - and the question is why should we
>say that the "Nat" runs cannot capture the first
>phase of 20th century warming when we have
>started them from cooler conditions, purely on
>the basis of the amount of warming achieved in
>the other runs by the time the reference period
>is reached. This seems harder to defend. It
>relates back to my earlier comments about (1)
>using as long a reference period as possible;
>and (2) thinking about climate changing from the
>relative stable period, rather than going
>backwards from the present period with its
>strong transient changes.
>If the decision is made to go with 1961-1990,
>then Keith suggests sticking with 1500-1899 for
>panels (a)-(d) as before, and make the new EMIC
>runs (currently panel (e)) into a stand-alone
>figure with 1961-1990 baseline.
>Views required urgently!
>Attachment converted: Macintosh
>HD:modelsA-E_2versions.pdf (PDF /�IC�) (00113BD7)
>Dr Timothy J Osborn
>Climatic Research Unit
>School of Environmental Sciences, University of East Anglia
>Norwich NR4 7TJ, UK
>phone: +44 1603 592089
>fax: +44 1603 507784
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
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