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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 10 Oct 2019

Submitted as: research article | 10 Oct 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Climate of the Past (CP).

Methodological and physical biases in global to sub-continental borehole temperature reconstructions: an assessment from a pseudo-proxy perspective

Camilo Melo-Aguilar1,2, J. Fidel González-Rouco1,2, Elena García-Bustamante3, Norman Steinert1,2, Johann H. Jungclaus4, Jorge Navarro3, and Pedro J. Roldan-Gómez1 Camilo Melo-Aguilar et al.
  • 1Universidad Complutense de Madrid, 28040 Madrid, Spain
  • 2Instituto de Geociencias, Consejo Superior de Investigaciones Cientificas-Universidad Complutense de Madrid, 28040 Madrid, Spain
  • 3Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), 28040 Madrid, Spain
  • 4Max Planck Institut für Meteorologie, Hamburg, Germany

Abstract. Borehole-based reconstruction is a well-established technique to recover information of the past climate variability based on two main hypothesis: first, that past ground surface temperature (GST) histories can be recovered from borehole temperature profiles (BTPs); and second, that the past GST evolution is coupled to surface air temperature (SAT) changes and thus, past SAT changes can be recovered from BTPs. Compared to some of the last millennium (LM) proxy-based reconstructions, previous studies based on the borehole technique indicate a larger temperature increase during the last centuries. The nature of these differences has fostered the assessments of this reconstruction approach searching for potential causes of bias. Here, we expand previous works to explore potential methodological and physical bias using pseudo-proxy experiments with the Community Earth System Model-Last Millennium Ensemble (CESM-LME). A heat-conduction forward model driven by simulated surface temperature is used to generate synthetic BTPs that are then inverted using singular value decomposition. This procedure is applied to the set of simulations that incorporate all the LM external forcing factors as well as those that consider the concentration of the green house gases (GHG) and the land use land cover (LULC) changes forcings separately. The results indicate that methodological issues may impact the representation of the simulated GST at different spatial scales, with the temporal logging of the BTPs as the main sampling issue that may lead to an underestimation of the simulated GST 20th century trends. Our analysis also shows that in the surrogate reality of the CESM-LME the GST does not fully capture the SAT warming during the industrial period and thus, there may be a further underestimation of the past SAT changes due to physical processes. Globally, this effect is mainly influenced by the GHG forcing whereas regionally, LULC changes and other forcings factors also contribute. These findings suggest that despite the larger temperature increase suggested by the borehole estimations during the last centuries of the LM relative to some other proxy reconstructions, both the methodological and physical biases would result in a underestimation of the 20th century warming.

Camilo Melo-Aguilar et al.
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Camilo Melo-Aguilar et al.
Camilo Melo-Aguilar et al.
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Short summary
This study explores potential sources of bias on borehole-based temperature reconstruction from both methodological and physical factors using pseudo-proxy experiments that consider ensembles of simulations from the Community Earth System Model. The results indicate that both methodological and physical factors may have an impact on the estimation of the recent temperature trends at different spatial scales. Internal variability arises also as an important issue influencing pseudo-proxy results.
This study explores potential sources of bias on borehole-based temperature reconstruction from...