Although quantitative isotopic data from speleothems has been used to evaluate isotope-enabled model simulations in the past, currently no consensus exists regarding the most appropriate methodology through which achieve this. Motivated by the fact that a number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, we have explored different approaches on how to use speleothem data for data-model comparisons in a paper that is now open for discussion at Climate of the Past Discussions (https://www.clim-past-discuss.net/cp-2019-25/):
Comas-Bru, L., Harrison, S. P., Werner, M., Rehfeld, K., Scroxton, N., Veiga-Pires, C., and SISAL working group members: Evaluating model outputs using integrated global speleothem records of climate change since the last glacial, Clim. Past Discuss., 2019, 1-53, 10.5194/cp-2019-25, 2019.
In this study, we show that the SISAL database reproduces the first-order spatial patterns of isotopic variability and is therefore useful to assess a model’s ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotopic data for model evaluation, including screening the observations, the optimum period for the modern observational baseline, and the selection of an appropriate time-window for creating means of the isotope data for palaeo time slices.
Figure 1 shows an example on how to circumvent the issue of speleothem records being discontinuous in nature, which complicates procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. This example illustrates a technique through which the absolute isotopic values during any time period could be used for model evaluation.
![](https://research.reading.ac.uk/palaeoclimate/wp-content/uploads/sites/78/Unorganized/BPP_BlogPost_Figure-01-1024x594.jpg)
Bartlein, P. J., Harrison, S. P., Brewer, S., Connor, S., Davis, B. A. S., Gajewski, K., Guiot, J., Harrison-Prentice, T. I., Henderson, A., Peyron, O., Prentice, I. C., Scholze, M., Seppä, H., Shuman, B., Sugita, S., Thompson, R. S., Viau, A. E., Williams, J., and Wu, H.: Pollen-based continental climate reconstructions at 6 and 21 ka: a global synthesis, Climate Dynamics, 37, 775-802, https://doi.org/10.1007/s00382-010-0904-1, 2011.
Harris, I., Jones, P. D., Osborn, T. J., and Lister, D. H.: Updated high-resolution grids of monthly climatic observations – the CRU TS3.10 Dataset, International Journal of Climatology, 34, 623- 642, https://doi.org/10.1002/joc.3711, retrieved from https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.01/ on November 2018, 2014.