Thursday, December 15, 2011


From: Jonathan Overpeck <>
To: Eystein Jansen <>
Subject: Re: [Wg1-ar4-ch06] comments to (mainly for Keith)
Date: Mon, 10 Jan 2005 14:40:27 -0700
Cc: Keith Briffa <>,,, joos <>

I agree; Keith should have the room, and section 6.5.8 should be
compatible - has Fortunat followed the discussion between
David/Stefan. Can you guys (David, Stefan, Keith, and Fortunat)
ensure this?

Thanks, Peck

>interesting discussion on an important topic. If space is the
>limiting factor we may have to evaluate whether to cut back on less
>central issues elswhere in the chapter. We will to a large extent be
>judged on how we tackle the hockey stick, sensitivity, unprecedented
>20th century warming isuues in view of palaeo, and if a slight
>expansion is what it takes to do this properly, then I am
>sympathetic to that (without having heard Peck on the issue).
>At 16:32 +0000 10-01-05, Keith Briffa wrote:
>>thanks David
>>have to say that it is very difficult to say much in the minimal
>>space - and we really need a page to discuss the problems in the
>>reconstruction and and interpretation of the various forcings in
>>different models - I am just going to put this down in an over
>>abbreviated way and ask for specific corrections for you and Stefan
>>et al. The detail perhaps depends on what the final Figure looks
>>like and Tim is trying to put it together but lots of weird and
>>interesting stuff / questions arise as we do - especially relating
>>to past estimates of solar irradiance used by different people. At
>>15:29 10/01/2005, David Rind wrote:
>>>(I tried to send this earlier and it got hung up; apologies if it
>>>eventually gets through and you get a second version.)
>>>Well, yes and no. If the mismatch between suggested forcing, model
>>>sensitivity, and suggested response for the LIA suggests the
>>>forcing is overestimated (in particular the solar forcing), then
>>>it makes an earlier warm period less likely, with little
>>>implication for future warming. If it suggests climate sensitivity
>>>is really much lower, then it says nothing about the earlier warm
>>>period (could still have been driven by solar forcing), but
>>>suggests future warming is overestimated. If however it implies
>>>the reconstructions are underestimating past climate changes, then
>>>it suggests the earlier warm period may well have been warmer than
>>>indicated (driven by variability, if nothing else) while
>>>suggesting future climate changes will be large.
>>>This is the essence of the problem.
>>>At 9:28 AM +0000 1/10/05, Keith Briffa wrote:
>>>>THanks Stefan
>>>>At 21:13 07/01/2005, Stefan Rahmstorf wrote:
>>>>>some comments added in the text for the past millennium, plus I
>>>>>wrote some extra sentences on the implications of the dispute
>>>>>(repeated below).
>>>>>Hope it is useful,
>>>>>>Note that the major differences between the proxy
>>>>>>reconstructions and between the model simulations for the past
>>>>>>millennium occur for the cool periods in the 17th-19th
>>>>>>Centuries; none of these reconstructions or models suggests
>>>>>>that there was a warmer period than the late 20th Century in
>>>>>>the record.
>>>>>>A larger amplitude of preindustrial natural climate variability
>>>>>>does not imply a smaller anthropogenic contribution to 20th
>>>>>>Century warming (which is estimated from 20th Century data, see
>>>>>>Chapter XXX on attribution), nor does it imply a smaller
>>>>>>sensitivity of climate to CO2, or a lesser projected warming
>>>>>>for the future.
>>>>>Stefan Rahmstorf
>>>>>Wg1-ar4-ch06 mailing list
>>>>Professor Keith Briffa,
>>>>Climatic Research Unit
>>>>University of East Anglia
>>>>Norwich, NR4 7TJ, U.K.
>>>>Phone: +44-1603-593909
>>>>Fax: +44-1603-507784
>>>>Wg1-ar4-ch06 mailing list
>>>Wg1-ar4-ch06 mailing list
>>Professor Keith Briffa,
>>Climatic Research Unit
>>University of East Anglia
>>Norwich, NR4 7TJ, U.K.
>>Phone: +44-1603-593909
>>Fax: +44-1603-507784
>>Wg1-ar4-ch06 mailing list
>Eystein Jansen
>Bjerknes Centre for Climate Research and
>Dep. of Earth Science, Univ. of Bergen
>All�gaten 55
>N-5007 Bergen
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Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences

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