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Comparison of Large-Scale Proxy-Based Temperature Reconstructions over the Past Few Centuries M.E. Mann, Department of Environmental Sciences University of Virginia, USA S. Rutherford (U. Virginia, USA), T.J. Osborn (CRU, UK) EGS XXVI General Assembly Nice, France March 29, 2001
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OVERVIEW Review of Existing Proxy-Based Northern Hemisphere Temperature Reconstructions Sensitivity of Proxy-Based Estimates of Northern Hemisphere Temperature to: Conclusions Non-stationarity Differing proxies, distribution, Seasonality, Differing Statistical Methodology Regularized Expectation Maximization (“RegEM”) method
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Science
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MANN ET AL MULTIPROXY NETWORK Symbols: Tree – tree-ring; plus – PCs of dense tree-ring networks, star - ice core/ice melt, ‘C’ – coral, early instrumental- square – temperature – diamond – precipitation. From Mann et al., 1998.
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BRIFFA ET AL MXD DENDRO NETWORK
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MULTIPROXY MXD DATA
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Alternative Statistical Approach: (T. Schneider, Analysis of Incomplete Climate Data: Estimation of Mean Values and Covariance Matrices and Imputation of Missing Values, J. Climate, 14, 853-871, 2001) Regularized Expectation Maximization (“RegEM”) Algorithm
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Regularized Expectation Maximization Algorithm iterate Estimate Covariance Matrix Regularize with ridge regression Adjust Imputed Values
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SENSITIVITY TO NON- STATIONARY?
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submitted
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Training Interval Reconstruction Interval
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NINO3 INDEX
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SENSITIVITY TO TYPE OF PROXY DATA USED?
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Mann et al, Earth Interactions, 2000
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NORTHERN HEMISPHERE (0-90N) (ANNUAL MEAN)
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NORTHERN HEMISPHERE (0-90N) (ANNUAL MEAN)
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ANNUAL MEAN RECONSTRUCTIONS
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SENSITIVITY TO STATISTICAL METHODOLOGY?
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ANNUAL MEAN COMPARISONS
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NOT MASKED MASKED WARM SEASON COMPARISONS (HEMISPHERIC)
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WARM SEASON COMPARISONS (EXTRATROPICAL)
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PATTERN CORRELATION
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CONCLUSIONS Main hemispheric trends in proxy-based climate reconstructions are robust with respect to the precise methodology, type of proxy indicators used, seasonality of reconstructions. Non-stationary during the calibration period does not seem to be important. The principle source of differences in hemispheric reconstructions is associated with spatial sampling variations. The next most significant source of sensitivity of hemispheric reconstructions is the precise nature of the statistical reconstruction methodology
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