Thursday, December 29, 2011


cc:, "'Tim Osborn'" <>, "'Fortunat Joos'" <>, "'Jonathan Overpeck'" <>, "'David Rind'" <>, "'Bette Otto-Bleisner'" <>,, "'Ricardo Villalba'" <>,, "'Valerie Masson-Delmotte'" <>, "'Dominique Raynaud'" <>, "'Keith Briffa'" <>, "'Phil Jones'" <>,,,,,,, "'Thorsten Kiefer'" <>, "'Eric W Wolff'" <>,,,,,, "'Michael Schulz'" <>,, "'Bette Otto-Bliesner'" <>,,,,,, "'Laurent Labeyrie'" <>, "'Gavin Schmidt'" <>
date: Wed, 15 Apr 2009 11:46:30 +0200
from: Stefan Rahmstorf <>
subject: Re: AW: Key new IPCC relevant paleo-science
to: "'Eystein Jansen'" <>

Dear Eystein and Peck,

I can also see arguments for either version. A full integration of paleo
information throughout the report would be great - if done well. But for
practical reasons I think a separate paleo chapter is likely to work
better, simply because of the expertise of people and the way IPCC works
chapter by chapter. You need to bring people with paleo expertise
together for discussion and writing of the relevant text. If you want
the paleo information spread around all chapters, you need people with
paleo expertise on each chapter - and more than one person.
Unfortunately, most colleagues dealing with modern climate still have
little knowledge about paleo issues. Therefore, getting the paleo people
together in one chapter seems the more practical way to proceed and more
likely to bring a critical mass of paleo experts together for thorough
discussion of the available evidence.

However, I think it will be essential then to take some steps to insure
a better integration of the paleo information with the rest of the
report, especially when it comes to drawing conclusions about the
future. We all remember the problems we had with this last time. The
future projections chapter 10 dealt almost exclusively with GCM results;
no discussion about issues like sea level or risk of abrupt change based
on paleo results was included there. On the other hand we were
"forbidden" to have such a discussion in the paleo chapter, with the
argument that any discussion of the future should be left to chapter 10.

One way around this that has been discussed recently is to have one
chapter on "Model simulations of future climate change scenarios" which
is like the old chapter 10, but then followed by a chapter providing an
overall "Assessment of future climate risks". This would be based on a
critical discussion of all evidence - the GCM projections shown in the
previous chapter, but also recent observations and paleo evidence. It
could provide a discussion of what GCMs are not yet good at (sea level /
ice sheets / abrupt changes / methane release from permafrost etc) and
what we know about those risks. I.e., such a chapter would not just give
"best guess" scenarios for future climate but a full risk assessment, as
requested by governments. This would overcome the previous chapter 10
attitude (quote: "if it's not in a GCM it is speculation, and IPCC does
not deal in speculations") which has lead to the problems the AR4 had
e.g. with the sea level issue by focusing only on what current models give.
I would strongly support this approach - it would need to be agreed at
the scoping meeting; once the chapter structure is fixed, it will be too
late to get this right.

Cheers, Stefan

Stefan Rahmstorf


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