From	Jonathan T. Overpeck	Date	Wed, 12 Jan 2005 16:55:36 -0700
To	Bette Otto-Bleisner, Keith Briffa, Tim Osborn, Eystein Jansen, peltier@atmosp.physics.utoronto.ca, Stefan Rahmstorf, cddhr@giss.nasa.gov
CC	Dominique Raynaud, Jean-Claude Duplessy
Subject	Urgent - FINAL review/edits of 6.5.8 Sensitivity
Hi all on the list above... Some of you have received this already straight from David, but some other key people have not. Eystein and I would appreciate it very much if you would please read/comment/and edit the attached section 6.5.8 (Sensitivity) NO LATER THAN THURSDAY NOON, Eastern time (6PM GMT). Please send responses to all on the address list ABOVE, plus Peck. Thanks, Peck X-Sieve: CMU Sieve 2.2 X-Sender: drind@4dmail.giss.nasa.gov Date: Wed, 12 Jan 2005 13:29:53 -0500 To: joos From: David Rind Subject: Re: Fwd: Re: Fwd: 6.5.8 Sensitivity Cc: David Rind , Jonathan Overpeck , Dominique Raynaud , Eystein Jansen , trond.dokken@bjerknes.uib.no, peltier@atmosp.physics.utoronto.ca, Jean-Claude Duplessy , rahmstorf@pik-potsdam.de, cddhr@giss.nasa.gov X-Virus-Scanned: amavisd-new at email.arizona.edu X-Spam-Status: No, hits=-2.272 required=7 tests=BAYES_00, HTML_20_30, HTML_MESSAGE, MIME_SUSPECT_NAME X-Spam-Level: Dear Fortunat (and others), Here is the revised section 6.5.8. I've put in most of your changes (and also most of those suggested by Stefan, particularly with regards to clarifying the sign of the radiative forcing). Most importantly, I've removed the table - I agree it seems to imply a solidity that is really not there. The one thing I have not done is condense it greatly (of course!). The real reason for going into such detail, rather than just saying, "well, the forcing and response are uncertain, so we can't conclude anything", is I think it's important to show that paleoclimate scientists have gone to some effort to try to deduce climate sensitivity from the paleorecord, the parameter that is probably of most interest to IPCC. In that respect the details are important, as are the magnitudes of uncertainty represented in the different studies. Obviously, at any point in the proceedings the section can be shortened, but I thought it useful to start with this level of quantification, and show paleoclimate has this similarity with the rest of IPCC in addition to more qualitative concepts. I've responded to your individual comments below. At 6:15 PM +0100 1/11/05, joos wrote: Dear David, Here my comments on the updated climate sensitivity section. Please apologize if I formualate my comments straight away, but I need to leave very soon. Many of my comments might have to do with presentation. Your main conclusions in paragraph f are fine. My view is that it would be ideal to address the issue from a probabilistic view point. this is of course not always possible. 1) Maunder Minimum section: Several studies using Monte Carlo approaches show that almost any climate sensitivity is posssible when taking into account uncertainties in radiative forcing input data as well as observational records over the 20 century as constraints. See the Paris report for more information. The uncertainty does not only arise from indirect aerosol effect, but also form the whole range of forcing agents that all have an uncertainty attached. E.g. Reto Knutti did some evaluation of his results where he assumed that the aerosol forcing is exactly know (No error) -> even then climate sensititivity remains unconstraint. Clearly, uncertainty is growing when going further back in time than the last century as done here. Then, the numbers provided in the table are useless, as you now state in the last sentence of the revised text. 2) Other sections: I think similar concerns also hold for the other sections. For example, the LGM global cooling is very uncertain. I have just heard yesterday a talk by Ralph Schneider who showed how different SST reconstructions (Alkenone, Cd/Ca, MAT, radiolare etc) disagree. global SST cooling might be anywhere between 0 and 4 K or so. Of course, CLIMAP and the recent GLAMAP update provide a reasonable estimate. However, the point is that uncertainies are huge. The table is a very focused and stand alone thing for the reader. It gives the impression that climate sensitivity for different period can be well evaluated. However, this is not the case. 3) My conclusion: - The table should be dropped. I have quite a strong feeling here, as it seems to me that the number in the table are very hard to defend and should not be made prominent. The table and reference to it has been dropped. - The whole section should be condensed considerably. Your main conclusions in paragraph f are fine. Well, removing the table will shorten this section! Further comments: 1) section d) 1. para: solar forcing reduction estimate range up to 0.65% for MM e.g. Reid, 97 and Bard et al. Correction made, and reference added (and I also corrected the numbers as Stefan suggested, although the upper number is actually larger given the Reid estimate). 2) section d, last para equilibrium The statement that transient effects are not important is very hard to defend: 2a) The warming and forcing up to today is considered. Certainly, we are now far from equilibrium ( a lag of 30 years or so). 2b) the volcanic forcing is very pulse like and I do not see how the equilibrium concept holds here. It can only be evaluated in a transient way. 3c) The MM is probably not in equilibrium climate, as solar forcing has likely varied over the MM as indicated by radiocarbon, althoug sunspots were not present I've removed the word "transient" but I have justified the equilibrium aspect of the sentence with a reference (we investigated that issue by running from 1500 through the Maunder Minimum, and seeing what the prior changes in solar forcing did to the Maunder Minimum cooling - the effect, as noted in the reference, was small in our model). 3) section b) end of 1. para: How should such a 'general climate sensitivity' be defined? For now I've simply suggested what should also be factored in; I don't know that it's our place to come up with a new definition per se, although if IPCC is interested, we could try! 4), section c) Somewhat a mix of model and observations. end of 2 para: It is not clear which forcing was operating in these different models (at least it is not stated in the text) and hence one can not directly imply a climate sensitivity in the way done here. For this the forcing that went into the model simulations must be known. I looked at each of the references and saw what forcing they actually used - they were all very similar except for one which used current orbital parameters (not really important). This comment is now included. Hope this is useful and looking foreward to further debate the issue. Thanks for the comments! David ps - Jonathan, the attached Endnote library includes the references we discussed yesterday, as well as all the ones relevant for this section. -- /////////////////////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////////////////////// -- 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 http://www.geo.arizona.edu/ http://www.ispe.arizona.edu/ Attachment Converted: "c:\eudora\attach\newest_6.5_2.8.doc" Attachment Converted: "c:\eudora\attach\IPPC_2007_1_Rind_Copy"