To: Caspar Ammann <firstname.lastname@example.org>
Subject: Re: [Fwd: Storch drift]
Date: Fri, 12 Aug 2005 11:21:20 -0400
Cc: Stefan Rahmstorf <email@example.com>, firstname.lastname@example.org, Keith Briffa <email@example.com>, Tim Osborn <firstname.lastname@example.org>, Phil Jones <email@example.com>
Thanks for the comments. Frankly, Von storch is being duplicitous here.
He may tell certain audiences (like the NCAR group last month) that he
is not suggesting that the GKSS simulation is reealistic, because he
knows he'll get skewered if he claims othewise. But then he turns around
to the press, and talks about how the Moberg et al reconstruction
matches their model, etc. I frankly consider this dishonest, at best!
If what Stefan says is true (that the entire long-term trend, including
the cold LIA in the model, is all due to the spinup problem), then it
completely invalidates the use of that model for testing statistical
reconstruction methodologies which require physically-consistent
patterns of variance in the calibration period to reconstruct the past.
But that's a separate issue.
As we now know, the far more damning fact is that Von Storch et al
knowingly applied a procedure which is not the MBH98 procedure, and they
think they can get away w/ admitting this now in some obscure Italian
journal which isn't even in the ISI database. Tim/Phil/Keith: you may
not know about the latter, but Caspar should be able to fill you in on
Meanwhile, lets enjoy the media fiesta on MSU...
Caspar Ammann wrote:
> this is very important news indeed. The runs will get a huge hit from
> this. The only way a coupled model can get a continued trend (without
> invoking an energy leak somewhere) is when there is a terrible
> deep-ocean spin up available even for their present day
> initialization, not to speak about the subsequent shock to
> pre-industrial conditions. Did you really say 1.5 degrees? Wow, that
> is quite a bit. Seems to me they must have used Levitus ocean data
> with an atmospheric restart file, then hit it with the solar/GHG
> changes. It seems rather large of a drop to come from a fully coupled
> stage. 1.5 degrees is about 30% too large to be exclusively from the
> atmospheric composition and solar irradiance, thus my suspicion
> regarding levitus. Now it would be important to know what happend
> because some people are using the run as a possible real-world
> scenario (although Hans in talks does not claim so).
> PS Now, bare in mind that the Science paper applies to the
> reconstruction, and for the general discussion the influence of spinup
> should not make that big of a difference (other than inflating the
> difference of the coldest period to the calibration period, which
> creates some issues discussed by Mike previously).
> Michael E. Mann wrote:
>> Storch drift
>> Stefan Rahmstorf <firstname.lastname@example.org>
>> Thu, 11 Aug 2005 15:37:27 +0200
>> Gavin Schmidt <email@example.com>, Keith Briffa
>> <firstname.lastname@example.org>, email@example.com
>> Hi Mike,
>> here is some interesting new info on the drift problem in the VS04
>> runs. Irina Fast and Gerd B�rger submitted a comment about this to
>> Science some months ago; it was rejected and they did not pursue it.
>> I'm trying to encourage them to resubmit this elsewhere. I do not
>> have the ms. but have seen several graphs. There are two key points.
>> 1. The ECHO-G run started at year 900, the VS04 paper of course shows
>> only results starting from year 1000. I've seen the full run now.
>> Between 900 and 1000, the NH temperature drops by about 1.5 �C!
>> That's how severe their initialisation problem is. From my experience
>> of how the THC responds after such step-function changes in forcing,
>> the strong warming from 1050-1150 in VS04 could well be a rebound
>> effect from the 1.5 �C cooling that precedes it, since the THC tends
>> to oscillate on such a time scale when forced rapidly.
>> 2. Irina has run ECHO-G initialised with modern climate and then
>> switching to pre-industrial conditions similar to the run shown by
>> VS04, but without any further variability in the forcing. Thus, this
>> shows the pure drift from initialising this run - this is what Tim
>> has been estimating in MAGICC. The actual drift in ECHO-G is even
>> larger and more persistent than what Tim found: there is a cooling
>> between the years 1000 and 2000 of over 0.6 �C, and this is an almost
>> linear trend over the whole time. I.e., not just drifting during the
>> first few centuries, but over the entire 1000-year period.
>> Cheers, Stefan
Michael E. Mann
Director, Earth System Science Center (ESSC)
Department of Meteorology Phone: (814) 863-4075
503 Walker Building FAX: (814) 865-3663
The Pennsylvania State University email: firstname.lastname@example.org
University Park, PA 16802-5013