In order to interpret quantitatively the paleoclimatic record of the past 800,000 years, computationally very efficient climate models must be used. This is achieved by the reduction of complexity in the climate system components that are modelled, primarily in the ocean and the atmosphere. Such Earth System Models of Intermediate Complexity (EMICs), pioneered by us in the early 1990s and further developed since then, permit multi-millennial integrations over entire ice age cycles , as well as massive ensemble simulations to obtain probabilistic estimates of climate relevant quantities. Our palette of EMICs that we have developed, the Bern2.5D and the Bern3D models, were employed to directly simulate quantities that are measured in paleoclimatic archives such as ice cores and ocean sediments (see Greenhouse Gas Concentrations in Ice Cores and Past Climate and Biogeochemical Studies in Ice Cores). Our recent studies have focused on noble gas concentrations for ocean temperature reconstruction, metal tracer distributions to quantify and understand past ocean circulation changes, or the effect of changes in orbital parameters on the habitability on planets. We have also used these models to project future climate change, in particular to quantify the rise of sea level projected for the next 1000 years, or to assess the implications of the combination of climate targets to avoid dangerous climate change.
We are currently using the Bern3D model, an Earth System Model of Intermediate Complexity, that consists of a 3-dimensional ocean circulation model (frictional-geostrophic) that is coupled to a moisture-energy balance model for the atmosphere and a thermodynamic sea ice model. In addition to a prognostic marine-land carbon cycle component including isotopes, the model is equipped with modules for noble gases Ar, Kr, and Xe, the noble gas isotope 39Ar, cosmogenic radionuclides 9Be, 10Be, and 14C, 230Th, 231Pa, 143Nd, and 144Nd. We also use the PlaSim model (Planet Simulator) to investigate the effect of changes in obliquity, irradiation, and planet mass on the atmospheric circulation structure. Recent model development activities concern the formulation of simplified ice sheet components that will be coupled to the Bern3D model.