cc: maureen.joseph@eci.ox.ac.uk, lindam@ucar.edu, m.hulme@uea.ac.uk, shs@leland.stanford.edu, peter.whetton@dar.csiro.au, giorgi@ictp.trieste.it, tkarl@ncdc.noaa.gov, cubasch@dkrz.de, ckfolland@meto.gov.uk, stocker@climate.unibe.ch, hewitson@egs.uct.ac.za
date: Tue, 22 Aug 2000 16:38:02 -0600 (MDT)
from: Jerry Meehl <meehl@meeker.ucar.edu>
subject: Re: Tables on extremes
to: Timothy Carter <tim.carter@vyh.fi>


Dear Tim,

I second the comments made by Mike Hulme concerning the table.  

Additionally, a recent modification was the addition of asterisks
to a few of the
model results in the table, and I include only these below: 

                               Obs                   Models 

Fewer frost days               virtually certain      likely*
                                                (higher minimum temps) 

More heat waves               inconclusive           very likely*
                                              (higher maximum temps)

fewer cold waves              very likely            very likely*
                                                 (higher miminum temps)

with the note at the bottom:

* no direct model analyses but physically plausible based on other
simulated model changes;
comparable changes simulated by the models are noted in parentheses

This takes into account that some of these categories (e.g. fewer frost
days) have not been explicitly documented in a model, but such changes
are "physically plausible" and could be shown if the models
were analyzed for such changes.  A couple of people commented that if
someone went looking for a paper where, for example, fewer frost days were
documented in a model, there wouldn't be such a paper.
You may want to reflect this in your table somehow.

Regarding
abrupt collapse of the THC, no AOGCM to date has ever spontaneously
simulated such a condition in any of the various scenario runs to 2100.
With very large forcing (4XCO2) the THC 
nearly stopped after some period of time 
(not abruptly) in one model but it re-started
again over time.
I have consulted with Ron Stouffer who has worked on the THC text for Ch.
9, and he has added the following sentence to the text of Ch. 9:

"It seems that the likelihood of a collapse of the THC is less
than previously thought in the SAR based on the AOGCM results to date."

This does not really address the "abrupt" collapse issue
per se, but is aimed
more at any collapse with almost any forcing and is thus more general.
Does this help out at all?

Best regards,

Jerry

 On Mon, 21 Aug 2000, Timothy Carter wrote:

> To: Barrie Pittock (Ch 3/WG II - Maureen at ECI: Please pass this on to
> Barrie)
>     Linda Mearns (Ch 10+13/WG I; Ch 3/WG II)
>     Mike Hulme (Ch 10+13/WG I)
>     Steve Schneider (Ch 1/WG II)
>     Peter Whetton (Ch 10+13/WG I)
>     Tom Karl (Ch 2/WG I)
>     Chris Folland (Ch 2/WG I)
>     Filippo Giorgi (Ch 10/WG I)
>     Bruce Hewitson (Ch 10/WG I)
>     Jerry Meehl (Ch 9/WG I)
>     Ulrich Cubasch (Ch 9/WG I)
>     Thomas Stocker (Ch 7/WG I)
> 
> Dear colleagues,
> 
> Some of you will be already be aware that Working Group II are in the
> process of constructing a (revised) table of extreme climatic phenomena
> based on WG I information. The Table is designed to portray globally
> generalised information on anticipated future changes in extremes as well
> as observed evidence for qualitatively similar changes in the instrumental
> record. We are using a typology of extremes described in Chapter 1/WG II
> (This is Steve Schneider's chapter, and I am attaching a marked up version
> of this table, tab1-1#2.doc, for Steve's comment following our Lisbon
> discussion and to inform other colleagues of our threefold classification
> of extremes).
> 
> Jerry Meehl recently circulated a draft Table with some of this extremes
> information summarised for Chapter 9, using the WG I confidence scale
> agreed in Victoria. Some of you may have already sent Jerry comments on
> this Table.
> 
> The Working Group II Table (in Chapter 3) used inputs from WG I following
> discussion among a few of us at a side meeting in Auckland on extremes
> (e.g. Tom Karl contributed some confidence measures for observed changes).
> 
> At the WG II meeting in Lisbon 2 weeks ago we revised this Table using new
> information from the draft Meehl et al. Chapter 9 Table. Our revised Table
> was circulated to the WG II authors and generated much discussion. 
> 
> In particular, WG II authors are very uncomfortable with the WG I
> confidence scale and we were strongly recommended to use the Schneider and
> Moss 5 point scale, which has been adopted by WG II.
> 
> We have also included information on Tropical Cyclones based on the Ch 10 Box.
> 
> Furthermore, we have added two "singular" phenomena (THC cessation and WAIS
> collapse), though these do not appear with confidence levels attached in
> Jerry's Table or elsewhere in WG I. They are of importance for impacts and
> we would like to include them.
> 
> On the basis of the discussion in Lisbon, I have redrafted the Table once
> again and am circulating it among the listed persons for comment
> (tab3-9#4.doc). Your suggestions would be much appreciated as this Table
> may well find its way into the TS and maybe even the SPM of WG II, because
> it is of obvious relevance to impacts work.
> 
> I would appreciate your comments and suggestions by 31 AUGUST (latest) so
> that I can make any necessary revisions before distributing this to the WG
> II authors.
> 
> 
> Finally ........
> 
> To Jerry, Ulrich and Thomas: Ch 9 has a statement on the THC slowdown in
> AOGCMs that is repeated in the SPM and has been repeatedly cited by the
> Global Climate Coalition, Saudi Arabia and some others who have read this
> through VERY CAREFULLY, to question the validity of any WG II exploratory
> impact assessments that relate to a possible cooling over Europe. 
> 
> "Most models show weakening of the thermohaline circulation (THC), which
> contributes to a reduction of the warming in the North Atlantic regions.
> Even in models, where the THC weakens, there is still a warming over Europe
> to to increased greenhouse gases."
> 
> However, there is apparently no statement on the likelihood of an abrupt
> COLLAPSE of the THC, though this has been modelled by intermediate
> complexity models and is reported in some detail in Ch 7/WG I, though not
> in the Ch 7 ES except in very vague terms (Thomas?). It is also explored in
> some detail in Chapter 19/WG II (Synthesis). I wonder if this "not
> impossible" scenario, which would mean large scale disruption of the
> climate over the North Atlantic region (probably including significant
> cooling) and is hence a low probability but high impact event, should be
> accorded some qualitative confidence rating too somewhere in WG I, to
> counterbalance the somewhat "optimistic" Ch 9 conclusion?
> 
> Any assistance (by 31 August!) would be much appreciated.
> 
> Best regards,
> 
> Tim Carter (Ch 3/WG II; Ch 13/WG I)
>