Thursday, May 3, 2012


cc: joos <>, Eystein Jansen <>, Bette Otto-Bleisner <>,, Keith Briffa <>
date: Fri, 01 Sep 2006 16:37:36 +0200
from: Stefan Rahmstorf <>
subject: Re: urgent IPCC need
to: Jonathan Overpeck <>

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 century.
- 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.
- [DEL: Paleoclimate model simulations are broadly consistent with the reconstructed NH
temperatures over the past 1000 years. :DEL] 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-20^th 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: [1]
(My former addresses are read by my assistant Brigitta.)

Stefan Rahmstorf

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