Saturday, March 17, 2012


date: Wed, 5 Jan 2005 17:53:34 -0700
from: Jonathan Overpeck <>
subject: [Wg1-ar4-ch06] Important chapter 6 coordination feedback from CLAs

Hi all Chap 6 LAs: There has been some debate about what material goes where, and how three
main sections of our chapter (3,4 and 5) should relate to each other and the rest of the
AR4 document. Attached and below is some specific guidance (look for your name in bold).
Please let Eystein and Peck know if there are any questions.

Section 6.2 is also key, but is focused more on methods, and is thus not part of the debate
that sparked the feedback below.

Thanks, Peck and Eystein.

Notes on required balance between Chap 6 Sections 3, 4, and 5
Input from Peck and Eystein for all LA and key CA's to read.
David Rind has brought up the issue of how discussion of forcing and paleo simulations fit
in to the various parts of the chapter. It is key that we reduce redundancy to a minimum,
and that the various sections cross-reference and support each other. Moreover, we want our
chapter to mesh well with the rest of the AR4 WGI report. Over the last12 hours we have had
lots of discussion, and Eystein and I propose the following plan:
1) section 6.3 (Understanding past change - various parts) - focus is on what climate
change happened and why, but only where relevant to policy. For example, for 6.3.2 - it's
all about whether late 20th century warmth etc is unprecedented and likely due to humans.
Can natural variability be a possible cause of what's happened over the last 100 years, and
if so, to what extent. Confidence?
Thus, in this section, have to include discussion of forcing and simulations in order to
assess (understand) the described past change.
Keith ( - your section can proceed as planned, with the figs you suggest (e.g.,
showing hypoth forcing, simulated change and reconstructed change). Need to work in
compatibility with the Chapter 2 discussion of solar and volcanic forcing. Read on
Valerie ( - both Eystein and Peck need to give you more specific feedback - you'll
get this soon, so please keep time open to work fast and furiously.
Dominique ( - you have material to integrate, but still a big job. Key is to keep
it focused on what is relevant to policy makers. Eystein's comments are key.
David and Stefan (Deep Time Box) - this is looking good - next iteration is nearing
completion according to David.
2) section 6.4. (Model Evaluation) - this section should be focused less (much less) on
what happened in the past, and more on how paleo supports or does not support the
performance of models (whole hierarchy) begin used by the IPCC to assess future climate
Can draw from Section 6.3, and should not be redundant.
Section leaders - please revise with the above in mind. Keep focused on model evaluation,
and only wrt to those models (categories of models) being used by other WG1 chapters to
assess future change.
3) section 6.5 (Synthesis) - this section is designed to pull thing together from all the
previous sections, as well as other chapters (e.g., chapter 2) and not yet tapped sources,
to make short key statements about topics highly relevant to policy makers. The section 6.5
subsections should cut across time scales and model types.
What are the key take home messages that haven't already been made in previous sections?
How can we make our chapter more seamless with others?
Keith - we have decided to eliminate Section 6.5.2. This means you can use any of that
prose (David's) as appropriate or needed. This frees up your section to integrate forcings
as planned in section
Fortunat and Dominique (6.5.3) - this section SHOULD have implications for the future, and
should be more explicit in terms of why the issues you raise in the existing prose is
relevant (e.g., CO2 feedback and orbital amplification - the point is that the climate
system can amplify subtle changes in forcing, but connect to policy implications)
Ricardo and Keith (6.5.4) - modes - this needs to be condensed and this might be made
easier by referring back to section 6.3 more. Otherwise, you are on the right track. I'll
try to get Julie Cole (we found a baby sitter!!) to help with the tropical part (for too). Maybe bring in Indian Ocean. Hopefully, you (Ricardo, since Keith is buried
in create the new section - stay focused on issues that are relevant to policy and
decision makers.

Ramesh and Valerie (6.5.5) - extremes - I've already contacted you both about this one.
Hopefully Valerie will add to Ramesh's good start, and I'll chip in as well. Let's Ramesh
work on 6.5.9
Jean-Claude and Dominique (6.5.6) - abrupt change - looking forward to seeing what you can
do here. Evaluate and integrate Fortunat's contribution as appropriate. Needs to complement
and not repeat what's in the other abrupt change sections you are help lead (6.3.3 and
Dick and Dominique (6.5.7) - sea level - need this soon!! This is straightforward in that
this is the primary place for sea level in our chapter. It must be focused on what's
relevant to policy makers - e.g., what paleo says about likely future sea level change.
Must also be well referenced, and can have a figure. Must anticipate and be complementary
to what's in other chapters. Lastly, needs to be 1 page single-spaced. I can help if
needed, but hope Dick and Dominique lead this in a strong manner.
David and Co (6.5.8) - you get a tad more space, but we like your focus on a QUANTITATIVE
analysis of forcing and response; and sensitivity. We're hoping you'll share your next
version with Stefan, Fortunat, Bette, and us as soon as you can. We understand that you
will have no figures.
Ramesh and Dan (6.5.9) - looking forward to something here - remember it must be relevant
to policy makers and not repeat what's in other parts of chapter. I suggest the main theme
be that paleo illustrates how global climate change will manifest itself regionally. In
many cases, the regional changes will be more extreme and hard to anticipate/predict than
broader scale (hemispheric and global) changes. Need to provide examples - drought, flood
frequency, storms, regional warming, monsoon shifts, etc, but be careful to complement,
rather than repeat other sections. Perhaps the trick is to make the extremes and abrupt
change sections above more generic and make the regional section more specific to certain
regions. In the end we might want a map of world with annotations of what the paleo
data/analysis suggests should be a major concern region by region. For example, in the SW
US, it's a) more frequent, longer drought, b) lower river flows c) increased occurrence of
large floods (which, by the way, usually don't help with drought), d) greater incursion of
tropical storm moisture (related to floods - both Pacific and Atlantic storms get into SW),
e) increased winter temps (more moisture stress if we get rid of sub-freezing weather, f)
more , decreased snowpack (less river flow), and g) much hotter temps. Paleo can only
inform - provide examples and proof that it can happen - a through d. The others are more
difficult to tease out of paleo, and should be left for the regional prediction chapter. I
could write this up if you'd like, but the key is to figure out a way to keep it to 2 pages
single spaced - perhaps provide an overview of the issue with a few key examples (chosen
strategically - maybe SW US, Europe, East Africa, and South Asia - can bring in sea level
rise too, and how that might combine with other factors (e.g., more tropical storms), and
an enhanced monsoon generated river flow/floods to really hurt coastal areas. Let me know
what I can do to help.
Please note that although we have gotten rid of two section numbers, we will stick with the
original section numbers for now to avoid confusion. This will change, of course, in the
final ZOD.

Thanks, 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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