Sunday, March 25, 2012

2852.txt

cc: Jonathan Overpeck <jtoatXYZxyzrizona.edu>, Keith Briffa <k.briffaatXYZxyz.ac.uk>, Eystein Jansen <eystein.jansenatXYZxyz.uib.no>, rahmstorf@pik-potsdam.de, drind@giss.nasa.gov, FortunatJoosatXYZxyzil.arizona.edu
date: Thu, 13 Jan 2005 12:57:08 -0500
from: David Rind <drindatXYZxyzs.nasa.gov>
subject: Re: 6.5.8 revisions
to: Tim Osborn <t.osbornatXYZxyz.ac.uk>

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Hi Tim (and others),

Thanks for your comments.

I've looked at the suggested changes (in red on Tim's document) and I
basically agree with them. I've incorporated them into the
accompanying version. We cannot, however, avoid using the Late
Maunder Minimum time period to assess climate sensitivity for a
number of reasons, but primarily because so many people have tried
doing it (as indicated by the references). In addition, it relates
very strongly to two main topics of controversy: the possible
importance of solar forcing (for which this period is the poster
child), and the validity of the "hockey stick" reconstruction. I
think the conclusion, that there is too much uncertainty to derive a
meaningful result, is not a negative one - it's something that needs
to be said, in the face of the tendency of some people to say the
opposite. The only way to clearly show this is through the details as
provided.

With respect to "equilibrium climate" and the presence of volcanos:
volcanic aerosols do not last long enough in the atmosphere (~one
year residence time)to throw models significantly out of radiative
balance when 50 year runs are being considered. Nor do they induce
large ocean surface temperature changes, much less interaction with
the deeper layers of the ocean which is what adds an unresolved
cooling (or warming) and induces larger radiative imbalances. It is
the latter component that is the chief difference between the
transient simulations and equilibrium simulations for CO2 changes,
for example. The only way that volcanos (or any climate forcing) can
force the system out of radiative balance is to provide large and
continuing trends (like is happening now); over this time period,
none of the model simulations had that. (The other way is to have
large forcing trends prior to this time period - and that's discussed
in the following sentence in the text.) Anyway, to avoid confusion,
I've removed the term equilibrium and now refer to radiative balance.

[I assume the figures Tim referred to (and which I now refer to in
the text) have been shown in Keith's section previously; they
certainly should not be waiting for the end of this chapter to make
their first appearance. It's not mandatory that they be referred to
here, but if they already exist, it's useful to relate to them.]

David


At 4:19 PM +0000 1/13/05, Tim Osborn wrote:
>At 23:50 12/01/2005, Jonathan Overpeck wrote:
>>Toward that end, I wonder if you two (or maybe just Tim if Keith is
>>working more on 6.3.2.1) could read and comment/edit on:
>>
>>Section 6.4.3.2 -evaluation of transient model runs of the last millennium
>>
>>and
>>
>>Section 6.5.8 - synthesis of climate sensitivity issues
>>
>>Eystein and I are asking that you do this FAST because these
>>sections must be compatible with your section 6.3.2.1 (and because
>>you guys know as much as any about the material in these two other
>>sections!).
>
>Dear Peck (plus cc to others - have I sent it to the appropriate people?),
>
>Keith and I have looked at these sections and the attached documents
>contain my tracked changes. They seem to be compatible with Keith's
>section and the figures. We've put in a couple of simple
>cross-references to the figures from Keith's section. Plus some
>minor changes. Plus some comments, particularly about the
>section(d) of the climate sensitivity section. Keith expands upon
>these latter comments with the following:
>
>--------------------
>It would be wise NOT to refer to the Maunder Minimum time period.
>Anyway, 1675-1715 is (by most opinions) the LATE Maunder Minimum (an
>accidental name that derives from the random non-availability of
>documentary/paleo data for the earlier part of the period in some
>[Swiss] study by Pfister and people). Up to then, MM was taken to
>be 1645/50 to 1715. By using this terminology you divert objective
>analysis of TOTAL forcing change (particularly given volcanic
>uncertainty).
>
>The definition of "today" is also crucial as it affects (albeit not
>precise) estimation of forcing changes from the earlier period. The
>wider the comparison base, the more imprecise the estimates. The
>narrower the base, the more you could argue about likely
>non-equilibrium (see Tim's comment in attached document).
>
>The volcanic forcing likely means that the LMM is likely not in
>equilibrium either! Nice if base period for estimates of changes
>(forcings and temperatures) could be compatible with the base period
>used in Figure 1).
>
>We will cross reference this section from ours.
>--------------------
>
>Cheers
>
>Tim and Keith
>
>
>Attachment converted: Toltec:6.4.3.2_osborncomments.doc (WDBN/MSWD) (0008C15A)
>Attachment converted: Toltec:6.5.8_osborncomments.doc (WDBN/MSWD) (0008C15B)
>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


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