from: Tom Wigley <wigleyatXYZxyz.ucar.edu>
subject: Re: past 1000 yr
to: Tim Osborn <t.osbornatXYZxyz.ac.uk>
Tim Osborn wrote:
> Hi Tom - I'd be happy to contribute if I have something worth
> contributing! I'm a bit rushed today and away tomorrow, but can
> respond to further emails later in the week.
> At 14:31 03/10/2004, Tom Wigley wrote:
>> Caspar Ammann and I plan to publish some MAGICC
>> results for the past 100 years.
> Presume you mean 1000 years, hence relevance of ECHO-H/von Storch.
>> Part of the reason is the new
>> solar forcing, as in my Science note with Peter Foukal.
> Yes I saw that. With a brief scan I didn't realise that you were
> presenting a new forcing history, just discussing reasons why
> long-term changes may be lower than previously estimated. But
> presumably you can use such reasoning to develop a new forcing history
> - or, better, a range or even a PDF of such histories. And then
> extend it using 14-C or 10-Be, or a combination?
WE SAY *NO* LOW FREQ FORCING. C-14/Be-10 ARE PROXIES FOR MAGNETIC FIELD
IS NO ADEQUATE THEORY RELATING THESE TO LUMINOSITY CHANGES -- IN FACT
THEY ARE *NOT* RELATED. SO WE ARE SUGGESTING A DIFFERENT FORCING
IMPLICATIONS AS IN THE FIGURE. NO SOLAR-INDUCED LIA, IN ACCORD WITH THE
RECONSTRUXIONS. FURTHER, THERE IS SOME RECENT WORK SUGGESTING THAT PART
C-14/Be-10 CHANGESW ARE DUE TOCHZNGES IN THE *EARTH'S* MAGNETIC FIELD.
>> So we
>> address both forcing and senstivity uncertainties. In
>> addition, the drift due to incorrect initialization is an issue.
> Surely not so in MAGICC? But yes, it is in GCMs and particularly so
> in ECHO-G.
OF COURSE WHAT I MEAN IS TO USE MAGICC TO QUANTIFY THE INITIALIZATION
>> I have not yet read the Storch paper or your comment -- but
>> did you mention this problem?
> We said that ECHO-G had a redder spectrum than other model simulations
> (there was no room to say that it showed greater fluctuations, but we
> cited the Jones/Mann paper which has an intercomparison figure in
> it). We didn't talk about the reasons for this (drift early on,
> strong solar forcing throughout and no tropospheric aerosols to
> mitigate recent warming) because we'd already said that the simulation
> didn't necessarily represent real climate history.
>> Also, can you remind me just what was done with the ECHO
> Main problem in terms of introducing "drift" (or "adjustment") was
> that they used a control run with present day CO2 as initial
> conditions. Although they allowed a 70-year spin-up (prior to AD
> 1000) to adjust back to pre-industrial CO2, this doesn't look long
> enough and the adjustment probably goes on for the first 400 years of
> the run - i.e. there is gradually disappearing cooling trend over this
> period. All based on MAGICC runs, but still fairly convincing
> (including non-zero heat flux out of the ocean in ECHO-G itself).
SEE THE STOUFFER PAPER IN CLIM DYN 23, 327 (2004).
>> If you have something to add on this, you can join as a co-author.
> I'm not quite sure what you plan, nor the input you need, but
> hopefully I can help.
WHAT I WOULD LIKE IS YOUR BEST ESTIMATE OF THE MAGNITUDE OF THE SPURIOUS
INITIALIZATION EFFECT IN
TERMS OF FORCING.
> Dr Timothy J Osborn
> Climatic Research Unit
> School of Environmental Sciences, University of East Anglia
> Norwich NR4 7TJ, UK
> e-mail: t.osbornatXYZxyz.ac.uk
> phone: +44 1603 592089
> fax: +44 1603 507784
> web: http://www.cru.uea.ac.uk/~timo/
> sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm