Saturday, May 19, 2012


cc:,,,,, Renato Spahni <>
date: Fri, 3 Feb 2006 15:03:26 -0700
from: Jonathan Overpeck <>
subject: Re: [Wg1-ar4-ch06] [Fwd: Greenhouse Gas Figure for IPCC]

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

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
>- 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.

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

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