Warm Paleocene/Eocene climate as simulated in ECHAM5/MPI-OM
1Max Planck Institute for Meteorology (MPI-M), Hamburg, Germany
2International Max Planck Research School on Earth System Modelling (IMPRS-ESM), Hamburg, Germany
Abstract. We investigate the late Paleocene/early Eocene (PE) climate using the coupled atmosphere-ocean-sea ice model ECHAM5/MPI-OM. The surface in our PE control simulation is on average 297 K warm and ice-free, despite a moderate CO2 concentration of 560 ppm. Compared to a pre-industrial reference simulation (PR), low latitudes are 5 to 8 K warmer, while high latitudes are up to 40 K warmer. This high-latitude amplification is in line with proxy data, yet a comparison to sea surface temperature proxy data suggests that the Arctic surface temperatures are still too low.
To identify the mechanisms that cause the PE-PR temperature difference, we fit a zero-dimensional energy balance model to the ECHAM5/MPI-OM results. Doubled pCO2 in PE compared to PR, increased atmospheric water vapour, and a slightly increased longwave cloud radiative forcing together cause about 2/3 of the PE-PR temperature difference; planetary albedo changes cause about 1/3. Our results support the hypothesis that local radiative effects as well as topographic changes, rather than increased meridional heat transports, were responsible for the "equable" PE climate.