The IPSL-CM4 model (Marti et al. 2010) couples four components of the Earth system: LMDZ-4 (Hourdin et al. 2006) for atmospheric dynamics and physics, OPA (Madec et al. 1997) for ocean dynamics, LIM (Fichefet and Maqueda 1997; 1999) for sea ice dynamics and thermodynamics, and ORCHIDEE (Krinner et al. 2005) for the land surface. Sulphate aerosols concentrations are externally imposed and direct and indirect aerosol forcings are considered (Quaas et al. 2004, Dufresne et al. 2005). This model participates to the CMIP3 project, the multimodel ensembles climate projections used in the intergovernmental panel on climate change (IPCC) assessment report (IPCC-AR4).
Two different resolutions of this model have been used:
Low resolution: 2.5°x4° (72x96L19) for the atmosphere and about 2°, with a meridional resolution of 0.5° near the Equator (149x182L31) for the ocean.
Mid-resolution: 1.25°x2.5° (143x144L19) for the atmosphere and about 2°, with a meridional resolution of 0.5° near the Equator (149x182L31) for the ocean.
IPSL-CM4-LOOP [Cadule et al., 2011] comprises a coupling between the IPSL-CM4 model and the two carbon cycle models: PISCES (Pelagic Interactions Scheme for Carbon and Ecosystems Studies) biogeochemical model [Aumont et al., 2003] for the ocean part and ORCHIDEE (ORganizing Carbon and Hydrology in Dynamic EcosytEms) model for the terrestrial part [Krinner et al., 2005]. PISCES includes 3 nutrients, 2 phytoplanktons, 2 zooplanktons, one detritus and semi-labile dissolved organic matter. It explicitly represents the collimation of phytoplankton growth by light and three nutrients: phosphate, iron and silicate. Two sizes are considered for both the phytoplankton (nano-phytoplankton and diatoms) and the zooplankton (micro-plankton and mesozooplankton). ORCHIDEE is a dynamic global vegetation model (DGVM) which calculates energy and hydrology budgets, carbon assimilation, allocation and decomposition and vegetation competition. ORCHIDEE distinguishes 13 PFTs amongst which the natural and agricultural vegetation distributions are prescribed. The vegetation carbon model is coupled to the atmosphere every 30 minutes, whereas monthly mean values were used in the older IPSL-CM2-C version of the model (Dufresne et al., 2002).