CPD Climate of the Past Discussions CPD 1814-9359 Copernicus GmbH Göttingen, Germany 10.5194/cpd-7-3325-2011 Impact of postglacial warming on borehole reconstructions of last millennium temperatures Rath V. 1 González Rouco J. F. 1 Goosse H. 2 Universidad Computense de Madrid, Facultad CC. Físicas, Departamento de Astrofísica y CC de la Atmosfera, Ciudad Universitaria, 28040 Madrid, Spain Centre de recherches sur la terre et le climat Georges Lemaître, Earth and Life Institute, Université Catholique de Louvain, 2 chemin du Cyclotron, 1348 Louvain-la-Neuve, Belgium 12 10 2011 7 5 3325 3347 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past-discuss.net/7/3325/2011/cpd-7-3325-2011.html The full text article is available as a PDF file from http://www.clim-past-discuss.net/7/3325/2011/cpd-7-3325-2011.pdf

The investigation of observed borehole temperatures has proved to be a valuable tool for the reconstruction of ground surface temperature histories. However, there are still many open questions concerning the significance and accuracy of the reconstructions from these data. In particular, the temperature signal of the warming after the Last Glacial Maximum is still present in borehole temperature profiles. It is shown here that this signal also influences the relatively shallow boreholes used in current paleoclimate inversions to estimate temperature changes in the last centuries by producing errors in the determination of the steady state geothermal gradient. However, the impact on estimates of past temperature changes is weaker. For deeper boreholes, the curvature of the long-term signal is significant. A correction based on simple assumptions about glacial-interglacial temperature changes shows promising results, improving the extraction of millennial scale signals. The same procedure may help when comparing observed borehole temperature profiles with the results from numerical climate models.

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