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Reconstruction data and information about valid analogues for "Technical Note: Considerations on using uncertain proxies in the analogue method for spatiotemporal reconstructions of millennial-scale climate"
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Description: 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 to consider the spatial covariance among proxy records. Beyond the last 2 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 its central estimate but large uncertainty ranges. The reconstruction by analogue provides not only a regional average record but also allows to assess 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.
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