Wednesday, December 21, 2011


From: Jonathan Overpeck <>
To: Gabi Hegerl <>
Subject: Re: cheers!
Date: Tue, 19 Sep 2006 11:37:49 -0600
Cc: Keith Briffa <>, Eystein Jansen <>

Hi Gabi - we do loose quite a bit (e.g., boreholes and other proxies)
back beyond 500, so that's why we drew the "very likely" line there.
But, we did stay as strong as the TAR back 1300, so that was our
compromise on certainty. I believe the forcing series also start to
get more uncertain pretty fast back beyond even 400 years ago, but
I'm pretty impressed with the match between simulated and observed NH
climate back ca. 700 years (e.g., our Figs 6.13 and 6.14). Thus, I
bet you are right that we know back to 700 pretty well, but not well
enough to go with "very likely" in the all important chap 6 bullet.

Not sure this helps, but we do need to pay attention as we do the SPM
to get the right balance.

I'll cc to Keith in case he wants to chime in, which would be appreciated.

thanks, peck

>p.s. hope you are all recovered etc!
>I have one chapter question: We were waffling back and forth if we
>SHOULD go with the chapter 6
>assessment on the last 500 being better reconstructed than say last
>700, but in the end, we stuck with
>last 700 because some results rely on using a long timehorizon to
>separate like ghg and solar signals.
>To say that very likely a substantial fraction of the variance on
>those records is externally forced (nother
>words, detectable external signals in reconstructions).
>Does this seem ok to you? In the SPM session we had some waffling
>about 5 vs 7 centuries.
>Jonathan Overpeck wrote:

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

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