date: Fri, 19 Nov 2004 08:20:01 -0500
from: "Michael E. Mann" <mann@virginia.edu>
subject: Re: draft paragraph for PAGES/CLIVAR
to: Keith Briffa <k.briffa@uea.ac.uk>, valerie.masson@cea.fr, beer@eawag.ch, gschmidt@giss.nasa.gov

   Thanks Keith,
   Your changes look great. I agree that "competing" was a bad word, has an unintended
   negative connotation...
   Will make all of these changes and send on to the working group co-chairs,
   Mike
   At 06:02 AM 11/19/2004, Keith Briffa wrote:

     Dear Mike et al.
     sorry to be slow - but here are my very few suggested modifications of the paragraph
     (shown in italics) . I did not the use of the word competing - as used to describe the
     different reconstructions-  as they are not. The other bits are just to add emphasis
     slightly differently.
     Cheers and looking forward to meeting next time .
     Keith
     At 17:11 15/11/2004, Michael E. Mann wrote:

     sorry, one slight revisions (I added on one sentence at the end to specifically address
     the two bulleted points that were listed with this item).
     Climate Variability over the Last Few Millennia

     Well-dated, high resolution proxy reconstructions and model simulations, incorpoating
     estimates of natural forcings, both suggest that late 20th century warmth at a
     hemisheric or global scale is anomalous in the context of the past 1000-2000 years.
     Significant differences exist, however, between various published estimates. Some
     differences between estimated extratropical and full (combined tropical and
     extratropical) hemispheric mean temperature changes in past centuries may be consistent
     with seasonal and spatially-specific responses to climate forcing. Forced changes in
     large-scale atmospheric circulation such as the NAO, and internal dynamics related to El
     Nino, may play an important role in explaining regional patterns of variability and
     change in past centuries.  Despite progress in recent years, important uncertainties and
     caveats exist, however, with regard to both empirical reconstructions and model
     estimates. One important issue relates to the varying seasonality and spatial
     representativeness of  different estimates.  Another important issue involves the
     reliability of the statistical methods used for proxy-based climate reconstruction. To
     date, only limited work has been done using common predictor sets to compare the
     fidelity of reconstructions based on different techniques and even these appear to yield
     contradictory results concerning the potential underestimation of long-term trends.
     Further work is required in this area.  An additional important issue involves the
     reliability of estimates of past climate forcing used to drive simulations of climate
     change over the past millennium or longer.  Dramatically different estimates of volcanic
     and solar radiative forcing, in particular, have been used in various different
     simulations, making a direct comparison among simulations difficult. Further work is
     also required to develop improved, concensus estimates of various radiative forcings,
     and in the case of coupled model simulations, the use of appropriate ensembles of
     simulations ( including those driven with common forcings) over the past few millennia.
     At 12:00 PM 11/15/2004, Michael E. Mann wrote:

     Dear Keith, Valerie, Juerg, and Gavin,
     First, I wanted to say that I enjoyed seeing and talking with each of you last week at
     the working group meeting. Looking forward to more of these get togethers in the future.
     I was asked to write a paragraph on the key scientific issues and questions related to
     the topic "Climate Variability over the last few millennia". Each of your names was also
     listed. So I've drafted a paragraph, and would like to get your suggestions. I'd like to
     submit this Friday, so please get back to me before then. If I don't hear from you by
     then, I'll assume you're ok w/ the current wording...
     Thanks in advance for your help,
     mike
     Climate Variability over the Last Few Millennia

     Proxy reconstructions and model simulations both suggest that late 20th century warmth
     is anomalous in the context of the past 1000-2000 years.  Significant differences exist,
     however, between various competing estimates. Some differences between estimated
     extratropical and full (combined tropical and extratropical) hemispheric mean
     temperature changes in past centuries may be consistent with seasonal and
     spatially-specific responses to climate forcing. Forced changes in large-scale
     atmospheric circulation such as the NAO, and internal dynamics related to El Nino, may
     play an important role in explaining regional patterns of variability and change in past
     centuries.  Despite progress in recent years, important uncertainties and caveats exist,
     however, with regard to both empirical reconstructions and model estimates. One
     important issue relates to the varying seasonality and spatial representativeness of
     competing estimates.  Another important issue involves the reliability of the
     statistical methodologies used for proxy-based climate reconstruction including
     potential extensions back in time. Such methodologies have been tested using a long
     forced simulation of coupled climate models. Multiple such analyses, however, come to
     conflicting conclusions with regard to the likely fidelity of current methods used in
     proxy-based climate reconstruction.  An additional important issue involves the
     reliability of estimates of past climate forcing used to drive simulations of climate
     change over the past millennium or longer.  Dramatically different estimates of volcanic
     and solar radiative forcing, in particular, have been used in various different
     simulations, making a direct comparison among simulations difficult.
     ______________________________________________________________
                         Professor Michael E. Mann
                Department of Environmental Sciences, Clark Hall
                           University of Virginia
                          Charlottesville, VA 22903
     _______________________________________________________________________
     e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
              [1]http://www.evsc.virginia.edu/faculty/people/mann.shtml

     ______________________________________________________________
                         Professor Michael E. Mann
                Department of Environmental Sciences, Clark Hall
                           University of Virginia
                          Charlottesville, VA 22903
     _______________________________________________________________________
     e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
              [2]http://www.evsc.virginia.edu/faculty/people/mann.shtml

     --
     Professor Keith Briffa,
     Climatic Research Unit
     University of East Anglia
     Norwich, NR4 7TJ, U.K.

     Phone: +44-1603-593909
     Fax: +44-1603-507784
     [3]http://www.cru.uea.ac.uk/cru/people/briffa/

   ______________________________________________________________
                       Professor Michael E. Mann
              Department of Environmental Sciences, Clark Hall
                         University of Virginia
                        Charlottesville, VA 22903
   _______________________________________________________________________
   e-mail: mann@virginia.edu   Phone: (434) 924-7770   FAX: (434) 982-2137
            [4]http://www.evsc.virginia.edu/faculty/people/mann.shtml

