In recent years Arctic sea ice has been declining more rapidly than predicted by climate models. One question to be answered in this study is what the sole influence of a rapidly declining Arctic sea ice cover is on the global atmospheric and oceanic circulation as opposed to increased greenhouse gas concentrations. FESOM is the Finite Elemente Sea ice Ocean Model developed at the Alfred Wegener Institute. It has the advantage that it is possible to define a globally variable horizontal resolution and to focus on regions of interest such as the Arctic and coastal regions. This model has been coupled to the global atmospheric model ECHAM developed at the Max-Planck-Institute for Meteorology in Hamburg, Germany. The models are coupled using the OASIS coupler. A 360-year long control simulation with pre-industrial greenhouse gas and aerosol concentrations has been performed. After a spin-up phase of 160 years every 20 years simulations with a sudden ice albedo decrease and with a sudden CO2 increase have been branched off from the control simulation. Both the atmosphere and the ocean react differently to the different forcings. One of the most striking results is that the Atlantic Meridional Overturning circulation is strongly decreasing during the 20 years of sudden CO2 increase, while this is not the case for the simulations with sudden ice albedo decrease even though in both cases the Arctic sea surface salinity is decreasing due to the melting sea ice.