Keywords:climate modeling, Pliocene, Eocene
Warm periods of the past offer the chance to test climate models, not just through comparisons with proxy data, but also through model intercomparisons. The idea of an analogue to future global climate change, albeit with caveats, has additionally created much interest in these past periods. Two examples of these warm periods are the focus of intercomparison projects which have been established to utilize up-to-date paleodata to reconstruct formal boundary conditions for climate simulations. The Pliocene Model Intercomparison Project (PlioMIP), now in its second phase, focuses on the late Pliocene, approximately 3 Ma, while the Deep-Time Model Intercomparison Project (DeepMIP) looks back further to the period between the latest Paleocene and the early Eocene, approximately 55-50 Ma. Ice sheets in the polar regions are either smaller than those of today or are completely absent. Here, some results using the mid-resolution MIROC4m coupled atmosphere-ocean general circulation model will be presented. These results will focus on the most basic experiments specified in the projects, adhering to the protocols and using the boundary conditions provided. It is found that zonal mean sea surface and surface air temperatures exhibit stronger agreement with proxy data at low to mid-latitudes. Surface albedo and greenhouse gases are shown to contribute greatly to warming, especially at high latitudes. In the experiments using DeepMIP boundary conditions, different initial conditions can yield similar climate states but with differences in the Atlantic meridional overturning and downwelling in the Southern Ocean.