cc: k.briffa@uea.ac.uk, p.jones@uea.ac.uk date: Mon, 26 Mar 2001 13:56:14 -0600 from: tom crowley subject: Briffa et al reconstruction 2001 to: Tim Osborn Dear Tim, Keith, and Phil, Tim, thanks for the data. attached is a ps file comparing the Briffa et al 2001 time series rescaled to NH mean annual temp using the 1881--1960 interval for fitting (r = 0.81). The UKMO data set refers to the recent paper submitted to GRL. Also shown is a stretched version of a modified Crowley-Lowery time series (termed CL6) - the stretch refers to the rescaling required to agree with a model best fit to the instrumental part of the record (which in turn implies a sensitivity of about 3.0 C for a doubling of CO2) Over the interval 1407-1960 the decadally smoothed correlation between CL6 and Briffa.rescl is 0.76. The correlation from 1000-1993 of the model to the stretched CL6 record is 0.84 (0.94 over the instrumental record!), the residuals are better behaved in the TC Science paper, in the sense that there is now no misfit with the instrumental record. The stretched reconstructions would agree with the borehole estimates of temperature change over the interval 1600-1950. Another point of interest is that the CO2 drop of about 6 ppm from the 16th to 17th centuries could be intererpreted in terms of a global avg SST decrease of about 0.6 C - less than the 0.25 predicted by the CL6 record but comparable to the rescaled Briffa record (one problem with this constraint is that CO2 also seems to be low in the 18th century, so I need to think about this more). Any comments? If there is some agreement as to the legitimacy of this exercise several shortcomings in the Crowley 2000 study (the instrumental record disagreement), then some important advances in understanding. That still leaves the Mann et al record outside the fold but I continue to worry whether his calibration, which extends to 1980, results in a "flattening" of the regression line and overestimate of paleotemperatures that you people discussed in one of your Nature papers. Any comments? Tom Attachment Converted: "c:\eudora\attach\Briffa rescl NH ann.ps" Thomas J. Crowley Dept. of Oceanography Texas A&M University College Station, TX 77843-3146 979-845-0795 979-847-8879 (fax) 979-845-6331 (alternate fax)