The compact Earth system model OSCAR v2.2: description and first results

This paper provides a comprehensive description of OSCAR v2.2, a simple Earth system model. The general philosophy of development is first explained, followed by a complete description of the model's drivers and various modules. All components of the Earth system necessary to simulate future climate change are represented in the model: the oceanic and terrestrial carbon cycles - including a bookkeeping module to endogenously estimate land-use change emissions - so as to simulate the change in atmospheric carbon dioxide; the tropospheric chemistry and the natural wet-lands, to simulate that of methane; the stratospheric chemistry, for nitrous oxide; 37 halogenated compounds; changing tropospheric and stratospheric ozone; the direct and indirect effects of aerosols; changes in surface albedo caused by black carbon deposition on snow and land-cover change; and the global and regional response of climate - in terms of temperature and precipitation - to all these climate forcers. Following the probabilistic framework of the model, an ensemble of simulations is made over the historical period (1750-2010). We show that the model performs well in reproducing observed past changes in the Earth system such as increased atmospheric concentration of greenhouse gases or increased global mean surface temperature.