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Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data

Fig. 3. Comparisons between different Northern Hemisphere temperature reconstructions.
Comparisons between different Northern Hemisphere temperature reconstructions and instrumental record. Shown are smoothed (40 year lowpassed) reconstructions and, in the case of the Mann et al reconstruction, the associated 95% confidence interval. Shown for comparison are the HPS00 reconstruction, and the areally-weighted mean of gridded HPS00 borehole reconstructions. The borehole-derived temperature curves in this figure are as modified in the Rutherford and Mann 2004 correction (JGR 109, D1, 1107), corrected for an error in gridbox weighting. The original figure can be seen here.
Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data
J. Geophys. Res. - Atmospheres
Vol. 108 No. D7, 03 April 2003
doi: 10.1029/2002JD002532

Michael E. Mann1, Scott Rutherford 1, Raymond S. Bradley2, Malcolm K. Hughes3, and Frank T. Keimig2.

1 Department of Environmental Sciences, University of Virginia, Charlottesville VA, USA
2 Department of Geosciences, University of Massachusetts, Amherst MA, USA
3 Laboratory of Tree-Ring Research, University of Arizona, Tucson AZ, USA
We derive an optimal Northern Hemisphere mean surface temperature reconstruction from terrestrial borehole temperature profiles spanning the past five centuries. The pattern of borehole ground surface temperature (GST) reconstructions displays prominent discrepancies with instrumental surface air temperature (SAT) estimates during the 20th century, suggesting the presence of a considerable amount of noise and/or bias in any underlying spatial SAT signal. The vast majority of variance in the borehole dataset is efficiently retained by its two leading eigenvectors. A sizable share of the variance in the first eigenvector appears to be associated with non-SAT related bias in the borehole data. A weak but detectable SAT signal appears to be described by a combination of the first two eigenvectors. Exploiting this eigendecomposition, application of optimal signal estimation methods yields a hemispheric borehole SAT reconstruction that is largely consistent with instrumental data available in past centuries, and is indistinguishable in its major features from several published long-term temperature estimates based on both climate proxy data and model simulations.

Download the data from this study:

An error was made in the gridbox weighting in the original optimal weighted reconstruction, as described in
Rutherford and Mann 2004 Correction to Mann et al. 2003 Optimal Surface Temperature Reconstructions
The corrected versions of the optimally weighted reconstruction, plus other data files, are available below:

Raw gridded borehole trends
Reconstruction for each gridpoint
Optimal weighted reconstruction (corrected for gridbox weighting error, 2004)
Areally weighted mean reconstruction
EOF1, EOF2, PC1, PC2, and the Data Description.

The borehole data from the University of Michigan's Global Database of Borehole Temperatures is also available from the WDC Paleo Archive.

To read or view the full study, please visit the AGU website.
It was published in JGR Atmospheres, Vol. 108 No. D7, 03 April 2003 doi: 10.1029/2002JD002532

Support for this work was received from the Earth Systems History Program (NOAA and NSF), and Department of Energy (USA).

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National Oceanic and Atmospheric Administration
3 April 2003