Preprints
https://doi.org/10.5194/cp-2019-170
https://doi.org/10.5194/cp-2019-170

  16 Jan 2020

16 Jan 2020

Review status: a revised version of this preprint was accepted for the journal CP and is expected to appear here in due course.

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

 
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Oliver Bothe and Eduardo Zorita

Data sets

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: 08 Mar 2021
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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.