Sunday, June 3, 2012


date: Fri, 8 Sep 2006 20:52:08 +0200
from: Dominique Raynaud <>
subject: Re: [Wg1-ar4-ch06] Latest version of the Chap 6 Executive Summary
to: Jonathan Overpeck <>, IPCC Chapter 6 <>

Dear Peck and ch.6 LA's

I propose two modifications:

page 6-1 lines 15 to 19 and page 6-3, line 35. They are highlighted in cyan color.

The purpose is to make sure that we highlight that greenhouse gases very likely have played
a major role in the amplification process.

Have all a nice week end


Hi Chapter 6 LA's:

Please review the attached latest version of the chapter 6 executive summary. As before,
changes have only been made for the purpose of clarification - thank you to those who
provided feedback. Most changes (highlighted in yellow) are quite minor, however a
couple warrant some highlighting to make sure we have the optimal final wording:

1) the glacial bullet was debated by a couple team members and we decided that the
bullet needed to be more specific. For example, the use of the terms early and
mid-Holocene wasn't precise. So, how do you like:

o Glaciers of several mountain regions of the Northern Hemisphere retreated in
response to orbitally-forced regional warmth between 11,000 and 5000 years ago, and were
smaller at times prior to 5,000 years ago than at the end of 20th century, or were even

Note that this formulation also manages to get in the role of orbital forcing and the
fact that this orbital forcing caused regional, as opposed to hemispheric or global,
temperature anomalies. The revised bullet is also now more consistent with the glacial
box figure in terms of years cited. Ok?

2) Fortunat came up with the magic bullet (we think) describing the climatic
implications of the recent pre-industrial trace gas changes when he suggested:

The small preindustrial greenhouse gas variations also provide indirect evidence for a
limited range of decade- to century-scale variations in global temperature.

Sound ok to all?

3) Fortunat also queried regarding the why Europe, Asia and Australia were not included
along with parts of Africa and North America in the drought of the last 2000 bullet. The
reason for not including this other regions is that we don't have much evidence for
recurrent droughts lasting decades or longer in these other regions. They may have
happened, but the literature is apparently not well developed in this regard. Thus,
without the backup in the main text, we can't expand the bullet to include more regions.
No reviewers in any review cycle provided insights to change this assessment, so we feel
it's better to leave as it is. Also, it would be a substantive change to include them at
this stage - another reason to leave as is. Ok?

4) Then there is the tricky bullet on the amplification of orbital forcing. We
appreciate the debate on this one and suggest we go with the following:

Changes in greenhouse gas concentrations, ice sheet growth and decay, ocean circulation
and sea ice changes, biophysical feedbacks, and aerosol (dust) loading have very likely
influenced this amplification.

Note that the use of "influenced this amplification" (the "amplification" is a main
topic of the bullet - don't want to lose it) helps clarify that some of the listed
factors may have reduced the amplifications, some increased. Also, it makes the use of
the term "very likely" more sound - hard to imagine the factors listed played no roles.
Is this ok?

Again, many thanks for your input. Please note that we're close to having a CLA edited
(and shortened as necessary) complete final draft, and plan to circulate this early next
week for FAST final checking. Please set aside time so that you can read and suggest
final edits within 24 hours of receipt.

Best, Peck and Eystein


Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth

715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
direct tel: +1 520 622-9065
fax: +1 520 792-8795

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