cc: mmanning@al.noaa.gov, wg1-ar4-ch06@joss.ucar.edu, v.ramaswamy@noaa.gov, p.m.forster@reading.ac.uk, Marquis@ucar.edu, Renato Spahni <spahni@climate.unibe.ch>
date: Fri, 3 Feb 2006 15:03:26 -0700
from: Jonathan Overpeck <jto@u.arizona.edu>
subject: Re: [Wg1-ar4-ch06] [Fwd: Greenhouse Gas Figure for IPCC]
to: Valerie.Masson@cea.fr

Hi Valerie et al. - let's all weigh in before 
Renato generates the final SOD graphic. My 
thoughts

1) I don't feel strongly about the delta D data 
being smoothed or not (it makes sense, but will 
it make a difference? - go ahead if others 
agree), but I think we should keep isotopic data, 
rather than temperature - to avoid the confusion 
with the most recent data not being the warmest - 
or even close. It's regional temp, I know, but 
some readers might realize this. We can say in 
the caption that delta D is a regional temp 
record. I'm just one vote, here...

2) I agree with the vert grey shaded areas, and 
will go one step farther for a compromise. I vote 
we keep the shading on the real interglacials of 
the last 450kyrs, and delete the grey shading on 
the earlier "interglacials" - they are different, 
clearly, and we can make that point in the 
caption. Valerie's reasoning then works the other 
way - the grey shading helps readers get the 
point about how the length of interglacials 
comparable to the Holocene have varied, with MIS 
11 being the phattest.

Thanks, Peck

>Jonathan Overpeck a crit :
>
>>Hi Fortunat, Renato and friends: Here's my 
>>thoughts on what you have sent wrt to chap 6:
>>
>>1) for the EPICA/VOSTOK figure, I agree we 
>>should go with the version WITH N2O and WITH 
>>the anthropogenic increase 
>>(ipcc_ghg650kyr_v1ant) Renato - would you 
>>please resend with the delta D label fixed. 
>>Thanks - otherwise, nice job.
>>
>>
>I have a few comments on the figure ipcc_ghg650kyr_v1ant.
>
>- the deuterium data should be smoothed to 
>appear with a resolution similar to the GHG 
>records (we usually use step functions for 
>deuterium plots because the measurements are 
>conducted as averages for bag samples => not 
>single points).
>
>- it is possible to show temperature 
>fluctuations rather than deuterium, if you 
>prefer.
>
>- I am worried about the vertical grey lines on 
>this figure, assumed to define "interglacial 
>periods". It is tricky and depends on some 
>hypothesis (thresholds on deuterium or GHG). For 
>instance stage 7.5, 7.3 should also appear as 
>interglacials with the thresholds used for the 
>other warm periods.
>As we are aware of (preliminar) Dome C age scale 
>problems for stages 13-15, the grey bars may 
>give false impressions regarding the duration of 
>the oldest warm episodes.
>
>Valrie.


-- 
Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences

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