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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-170
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-170
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: technical note 16 Jan 2020

Submitted as: technical note | 16 Jan 2020

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This preprint is currently under review for the journal CP.

Technical Note: The analogue method for millennial-scale, spatiotemporal climate reconstructions

Oliver Bothe and Eduardo Zorita Oliver Bothe and Eduardo Zorita
  • Helmholtz Zentrum Geesthacht, Institute of Coastal Research, 21502 Geesthacht, Germany

Abstract. Inferences about climate states and climate variability of the Holocene and the deglaciation rely on sparse paleo-observational proxy data. Combining these sparse proxies with output from climate simulations is a means for increasing the understanding of the climate throughout the last ~ 21 millennia. The analogue method is one approach to do this. The method takes a number of sparse proxy records and then searches within a pool of more complete information (e.g., model simulations) for analogues according to a similarity criterion. The analogue method is non-linear and allows considering the spatial covariance among proxy records. Beyond the last two millennia, we have to rely on proxies that are not only sparse in space but also irregular in time and with considerably uncertain dating. This poses additional challenges for the analogue method, which have seldom been addressed previously. The method has to address the uncertainty of the proxy-inferred variables as well as the uncertain dating. It has to cope with the irregular and non-synchronous sampling of different proxies.

Here, we propose a specific way of dealing with these obstacles. We use uncertainty ellipses for tuples of individual proxy values and dates and, thereby, consider the dating as well as the data uncertainty. Results highlight the potential of the method to reconstruct the climate of the last ~ 15 millennia. However, in the present case, the reconstructions show little variability of their central estimates but large uncertainty ranges. The reconstruction by analogue provides not only a regional average record but also allows assessing the climate state compliant with the used proxy predictors. These fields reveal that uncertainty are also large locally. Our results emphasize the ambiguity of reconstructions from spatially sparse and temporally uncertain, irregularly sampled proxies.

Oliver Bothe and Eduardo Zorita

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Status: open (until 12 Mar 2020)
Status: open (until 12 Mar 2020)
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Oliver Bothe and Eduardo Zorita

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Reconstruction data and information about valid analogues O. Bothe https://doi.org/10.17605/OSF.IO/PJ9EG

Oliver Bothe and Eduardo Zorita

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Latest update: 26 Feb 2020
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Short summary
The similarity between indirect observations of past climates and information from climate simulations can increase our understanding of past climates. The further we look back the more uncertain our indirect observations become. Here, we discuss the technical background for such a similarity-based approach to reconstruct past climates for up to the last 22 thousand years. We highlight the potential and the problems.
The similarity between indirect observations of past climates and information from climate...
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