Modelling the mid-Pliocene Warm Period climate with the IPSL coupled model and its atmospheric component LMDZ4
1Laboratoire des Sciences du Climat et de l'Environnement/IPSL, CEA-CNRS-UVSQ, UMR8212, Orme des Merisiers, CE Saclay, 91191 Gif-sur-Yvette Cedex, France
2UPMC Université Paris 06, UMR7619, Sisyphe, 75005, Paris, France
3CNRS, UMR7619, Sisyphe, 75005, Paris, France
Abstract. This paper describes the experimental design and model results of the climate simulations of the mid-Pliocene Warm Period (mPWP, ca. 3.3–3 Ma) using the Institut Pierre Simon Laplace model (IPSLCM5A), in the framework of the Pliocene Model Intercomparison Project (PlioMIP). We use the IPSL atmosphere ocean general circulation model (AOGCM), and its atmospheric component alone, to simulate the climate of the mPWP. Boundary conditions such as sea surface temperatures (SSTs), topography, ice sheet extent and vegetation are derived from the ones imposed by the Pliocene Model Intercomparison Project (PlioMIP), described in Haywood et al. (2010, 2011). We first describe the IPSL model main features, and then give a full description of the boundary conditions used for atmospheric model and coupled model experiments. The climatic outputs of the mPWP simulations are detailed and compared to the corresponding control simulations. The simulated warming is 1.94 °C in the atmospheric and 1.83 °C in the coupled model experiments. In both experiments, warming is more important at high latitudes. Simulated precipitation has a different behaviour in the coupled model than in the atmospheric model alone, because of the reduced gradients in imposed SSTs, which impacts the Hadley and Walker circulations. In addition, a sensitivity test to the change of land-sea mask in the atmospheric model, representing a sea-level change from present-day to 25 m higher during the mid-Pliocene, is described. We find that surface temperature differences can be important (several degrees Celsius) but are restricted to the areas that were changed from ocean to land or vice versa. In terms of precipitation, there is no impact on polar regions although the change in land-sea mask is important in these areas.