date: Fri, 19 Nov 2004 08:20:01 -0500 from: "Michael E. Mann" subject: Re: draft paragraph for PAGES/CLIVAR to: Keith Briffa , 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