Laia Comas-Bru, Sandy P. Harrison, Martin Werner, Kira Rehfeld, Nick Scroxton, Cristina Veiga-Pires, Syed Masood Ahmad, Yassine Ait Brahim, Sahar Amirnezhad Mozhdehi, Monica Arienzo, Kamolphat Atsawawaranunt, Andy Baker, Kerstin Braun, Sebastian Franz Martin Breitenbach, Yuval Burstyn, Sakonvan Chawchai, Andrea Columbu, Michael Deininger, Attila Demeny, Bronwyn Dixon, Istvan Gabor Hatvani, Jun Hu, Nikita Kaushal, Zoltan Kern, Inga Labuhn, Matthew S. Lachniet, Franziska A. Lechleitner, Andrew Lorrey, Monika Markowska, Carole Nehme, Valdir F. Novello, Jessica Oster, Carlos Perez-Mejias, Robyn Pickering, Natasha Sekhon, Xianfeng Wang, Sophie Warken, Tim Atkinson, Avner Ayalon, James Baldini, Miryam Bar-Matthews, Juan Pablo Bernal, Ronny Boch, Andrea Borsato, Meighan Boyd, Chris Brierley, Yanjun Cai, Stacy Carolin, Hai Cheng, Silviu Constantin, Isabelle Couchoud, Francisco Cruz, Rhawn Denniston, Virgil Dragusin, Wuhui Duan, Vasile Ersek, Martin Finne, Dominik Fleitmann, Jens Bernd Fohlmeister, Amy Frappier, Dominique Genty, Steffen Holzkamper, Philip Hopley, Vanessa Johnston, Gayatri Kathayat, Duncan Keenan-Jones, Gabriella Koltai, Ting-Yong Li, Mahjoor Ahmad Lone, Marc Luetscher, Dave Mattey, Ana Moreno, Gina Moseley, David Psomiadis, Jiaoyang Ruan, Denis Scholz, Lijuan Sha, Andrew Christopher Smith, Nicolas Strikis, Pauline Treble, Ezgi Unal-Imer, Anton Vaks, Stef Vansteenberge, Ny Riavo G. Voarintsoa, Corinne Wong, Barbara Wortham, Jennifer Wurtzel, Haiwei Zhang

• Although quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for data–model comparisons. Here, we illustrate this using 456 globally distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothemAlthough quantitative isotope data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to using the speleothem data for data–model comparisons. Here, we illustrate this using 456 globally distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates the process of 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. To circumvent this issue, we illustrate techniques through which the absolute isotope values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model's ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotope data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on δ18O values, 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.…