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Modeling European and Arctic (Paleo)Climate at Regional Scales

Fig. 1: Description see text.

Together with several other German research institutions, the working group “Regional Climate and Water Cycle” participates in the project “From the Last Interglacial to the Anthropocene: Modeling a Complete Glacial Cycle”. This large joint project, funded by the German Ministry for Education and Research (BMBF), seeks to improve our understanding of the last glacial cycle (starting at about 130 ka BP) by extending and applying global and regional Earth system resp. climate models (ESMs, RCMs) to this period. The model results are compared with proxy data to validate the models, to assess the representativity of the proxies and to construct an observation and model based data framework to understand climate system dynamics and variability during the last glacial cycle with the ultimate goal to identify possible future climate trajectories beyond the present century during the next millennia.

Stable water isotopes (H216O, H218O, HDO) lend themselves particularly well for ESM and RCM validation purposes because they  are recorded in most paleoclimatic archives (e.g. ice cores, sediment cores, stalagmites) and the methods to model them with global and regional models are quite advanced. Stable water isotopes are fractionated during several transport-related phase changes, such as evaporation, cloud condensation, rainout, re-evaporation, and formation of ice. For this reason, the stable isotope ratio of atmospheric water vapor and precipitation is an especially powerful tool to validate the complex and variable hydrological cycle, especially precipitation and evaporation/sublimation, in models. We use a climate version of the isotope enabled regional climate model CCLMiso (originally developed at ETH Zurich as COSMOiso) to produce present and past regional climatologies of water isotopes for Europe and the Arctic. With our validation activities, we could show that the better accounting for regional effects with the higher resolution of the regional climate model resulted in an improved agreement between the model results and the observed data, as compared to the global model results. Fig. 1 shows a model-data comparison (with GNIP data) for the HDO excess δD in European precipitation for the period 2010 to 2014 in winter. The colored area is the mean modeled δD in precipitation, colored dots are the GNIP observations.

Future work will include steady-state climate simulations of mid-holocene and last glacial maximum; towards the end of this project we will complement the steady-state simulations by short transient simulations of Heinrich events and the Younger Dryas.

[Working group: Regional Climate and Water Cycle]