Wednesday, December 21, 2011


From: Jonathan Overpeck <>
To: Eystein Jansen <>
Subject: Re: urgent IPCC need
Date: Fri, 1 Sep 2006 15:25:20 -0600
Cc: Keith Briffa <>, Stefan Rahmstorf <>, Bette Otto-Bleisner <>,

Hi all - today has been a hectic one, with lots of good input from multiple folks. In the
end, we agreed to stick with our existing bullets, which changes only where they would
improve the clarity of what we were saying. Please check the attached - need Fortunat's
detailed look in particular. Changes are all in yellow highlight. Two special issues:

1) There is still concern that this bullet is too vague to be as useful as it could be:

o It is very likely that the global warming of 4 to 7 �C since the Last Glacial
Maximum (ca. 21,000 years ago) occurred at an average rate about ten times slower than the
warming of the 20th century.

but, perhaps the safest thing would be to leave as is.

2) As for the 1998/2005 warmest in last 1000 years issue, we suggest adding nothing new to
the ES, in line with our chapter policy from Bergen, BUT adding something in the chapter
along the lines of: " There is currently insufficient knowledge to form a consensus on the
issue of how the warmth of individual years of the last 100 years compare with individual
years of the last 1000 years" Keith, would you like to make a suggestion on the wording and

The reasoning expressed by Stefan on this issue is undoubtedly shared by others outside our
team, and perhaps a paper be written on this key topic to help the community reach better

Thanks for your continued dialog and work! Have a good weekend.

best, Peck and Eystein

dear All, thanks for being alert.
I think we have an agreement that Martin�s comments are useful, but that we should
change only those sentences where they clarify. Otherwise i agree with Stefan and
Keith�s statements below.
At 15:45 +0100 01-09-06, Keith Briffa wrote:

I forgot to say that I too disagree with removing the first sentence re simulations
being consistent with reconstructed NH temps. As Sefan says we need the context , and
our results are independent of Chapter 9 in this regard.
At 15:37 01/09/2006, Stefan Rahmstorf wrote:

Hi Peck,
Martin as in Manning? I have found his feedback very useful so far, so we should
definitely look at what he suggests - he mostly tends to look for whether our sentences
are clear. Obviously, he cannot suggest real changes in meaning, only issues of clarity,
but the latter I would take very seriously. Mostly I find his small rewordings good, I
comment on the larger points and exceptions below.
- I am against deleting the bullet on speed of deglacial change. This point is extremely
effective. Just two days ago an oil industry person told me that there have been big
natural climate changes like ice ages in the past, hence we need not worry. I responded
that the biggest warming in recent climate history was the end of the last Ice Age - but
that warming by about 5 �C took about 5,000 years, not a hundred. "Oh" he said, "Really
so long? I didn't know that." I think it is a very important point, we need to make it.
Maybe not in term of "average rate", may we should just say: the warming of 4-7 �C took
about 5,000 years, as compared to a future change of up to the same magnitude within a
- Next ice age bullet in 30k seems fine to me.
- exceptional warmth: the SPM said:
20th C T increase likely the largest in a millennium - that is strengthened (perhaps
very likely now?)
1990s likely the warmest decade in a millennium - that again is strengthened
1998 likely the warmest year - I'd say this is unchanged (except for 2005 challenging
it), likely is only 66%! Even though the annual proxy data may be uncertain, as a
physicist I would find it unlikely that there is a mechanism to cause a big warm outlier
year that beats 1998 from a much cooler background state. How would that work - where
would the heat come from?
So in my view we could actually say that these past SPM statements held up or were
strengthened - but in fact I also like the bullet as it is.

- Paleoclimate model simulations are broadly consistent with the reconstructed NH
temperatures over the past 1000 years. The rise in surface temperatures since 1950 very
likely cannot be reproduced without including anthropogenic greenhouse gases in the
model forcings, and it is very unlikely that this warming was merely a recovery from the
pre-20th century cold period.
On this I disagree with deleting the first sentence, as the second one needs it to
follow logically. And why should the paleo chapter suddenly make a statement on
post-1950 warming, if it is not in the context of the past millennium?
Cheers, Stefan
To reach me directly please use:

(My former addresses are read by my assistant Brigitta.)
Stefan Rahmstorf

Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.
Phone: +44-1603-593909
Fax: +44-1603-507784

Eystein Jansen
Bjerknes Centre for Climate Research and
Dep. of Earth Science, Univ. of Bergen
All�gaten 55
N-5007 Bergen
Phone: +47-55-583491 - Home: +47-55-910661
Fax: +47-55-584330


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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