From	Michael E. Mann	Date	Fri, 01 Dec 2000 12:58:19 -0500
To	Tim Osborn
CC	Scott Rutherford, Michael E. Mann
Subject	Re: New tree-ring density data
Scott, Tim, Here's the abstract. If the results pan out, then several us us may want to be discussing this work on the talk circuit. This is the first stab! Notice how safe (a very results-insensitive abstract!) mike XXVI General Assembly, Spring EGS Meeting Comparison of Large-Scale Proxy-Based Temperature Reconstructions Over the Past Few Centuries MANN, M.E.; RUTHERFORD, S; OSBORN, T.J. OA28.0 Study of past climates: Climate of the past millennium JOUZEL, J.; (co-conveners: JONES, P.D.; MANN, M.E.) Comparison of Large-Scale Proxy-Based Temperature Reconstructions Over the Past Few Centuries M.E. Mann(1), S. Rutherford(1), and T.J. Osborn(2) (1) Univ. of Virginia, USA, (2) Climate Research Unit, Univ. East Anglia, UK A promising approach to the problem of reconstructing patterns of past climate variability involves the application of spatial climate field reconstruction (CFR) techniques to networks of proxy climate indicators (e.g., Mann et al 1998;2000--see http://www.ngdc.noaa.gov/paleo/ei/ei_cover.html). This approach seeks to exploit the complimentary information in a diverse network of proxy indicators by determining the most consistent relationships between these networks of data and the leading spatial patterns of climate variability during a recent "calibration" period of overlap with the modern instrumental record. The calibrated relationship is then used to estimate large-scale patterns of climate variability in the past from the proxy data. This method makes no assumptions regarding the relationship between a given proxy indicator and specific local annual/seasonal climate variable, but does assume that the proxy indicator is tied to some combination of large-scale patterns of climate variability. Alternatively, it is possible to estimate large-scale temperature patterns from a relatively homogenous network of proxy climate indicators (e.g., tree-ring density data--see Briffa et al, 1998) by invoking a local calibration between each climate indicator and the climate variable (e.g., summer temperature) of interest. This approach is more conservative in the amount of information it seeks to extract from the proxy data network, but it is free from assumptions regarding the large-scale patterns of past climate variability. Recent reconstructions of Northern Hemisphere annual-mean and warm-season temperature patterns using these respective approaches and data show some similarities, but also some important differences. Here we investigate these differences more closely, examining the sensitivity of Northern Hemisphere temperature pattern reconstructions to (a) the underlying proxy data used, (b) the particular method used to estimate large-scale patterns from these data, and (c) the target seasonality of the reconstruction. By controlling independently for each of these three factors, we gain insight into the reasons for differences between various proxy-based estimates of past large-scale temperature variability. _______________________________________________________________________ Professor Michael E. Mann Department of Environmental Sciences, Clark Hall University of Virginia Charlottesville, VA 22903 _______________________________________________________________________ e-mail: mann@virginia.edu Phone: (804) 924-7770 FAX: (804) 982-2137 http://www.evsc.virginia.edu/faculty/people/mann.html