From	Tom Wigley	Date	Wed, 06 Oct 2004 11:58:16 -0600
To	Tim Osborn
Subject	Re: past 1000 yr
SEE CAPS 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. OOPS! YES. > > >> 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 CHANGES. THERE IS NO ADEQUATE THEORY RELATING THESE TO LUMINOSITY CHANGES -- IN FACT THEORY SUGGESTS THEY ARE *NOT* RELATED. SO WE ARE SUGGESTING A DIFFERENT FORCING HISTORY, WITH IMPLICATIONS AS IN THE FIGURE. NO SOLAR-INDUCED LIA, IN ACCORD WITH THE PROXY CLIMATE RECONSTRUXIONS. FURTHER, THERE IS SOME RECENT WORK SUGGESTING THAT PART OF THE 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 'DRIFT'. > > >> 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 >> run? > > > 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. > > > Cheers > > Tim > > > Dr Timothy J Osborn > Climatic Research Unit > School of Environmental Sciences, University of East Anglia > Norwich NR4 7TJ, UK > > e-mail: t.osborn@uea.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 > > >