Overview

Together with several other German research institutions, our working group participates in the project “From the Last Interglacial to the Anthropocene: Modeling a Complete Glacial Cycle”. This large joint project is funded by the German Ministry for Education and Research (BMBF) and 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 to this period. The model results are combined with homogeneised 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.

Emphasis is on the following topics:

1. to identify and quantify the relative contributions of the fundamental processes which determined the Earth’s climate trajectory and variability during the last glacial cycle,
2. to simulate with comprehensive Earth System Models (ESMs) the climate from the peak of the last interglacial (the Eemian warm period) up to the present, including the changes in the spectrum of variability, and
3. to assess possible future climate trajectories beyond the present century during the next millennia with sophisticated ESMs tested in such a way.

Our working group contributes to two subprojects: one consists in coupling an high resolution ice sheet model to the regional climate model COSMO-CLM with the aim to enable high resolution regional paleoclimate simulations with focus on the dynamics of ice sheets, to combine the results with proxy data and ultimately to derive coarse resolution ice sheet parameterisations for global models from these simulations. Presently, COSMO-CLM is being setup for the Greenland region and comparisons with recent observations are performed.

The other subproject deals with the regional modelling of stable water isotopes as a contribution to the observation and model based data framework: because stable water isotopes (H₂¹⁶O, H₂¹⁸O, HDO) are recorded in most paleoclimatic archives (e.g. ice cores, sediment cores, stalagmites) the data-model comparison will focus on this proxy. 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 in models. Stable water isotopes and relevant fractionation processes have therefore to be implemented into all components of the used ESMs. To account for the high spatial variability of isotope fields, dynamical downscaling with the regional model COSMO-CLM is applied. To this end, KIT has implemented stable water isotopes into all relevant components of COSMO-CLM. This work has benefitted considerably from a close cooperation with ETH Zürich, where water isotopes had already been implemented into the atmospheric and land surface component of the weather and forecast version of COSMO (COSMOiso).

The isotope enabled COSMO-CLMiso is currently validated against modern water isotope observations (Global Network of Isotopes in Precipitation and regular observations at KIT). Subsequent to this, steady-state climate simulations of mid-holocene and last glacial maximum will be carried out. Towards the end of this project we will complement the steady-state simulations by short transient simulations of Heinrich event 1 and Younger Dryas.