A suite of simulations, with a new high-resolution climate model (CM2.5) developed at GFDL, were used to study the observed long-term decline of winter rainfall over parts of southern Australia. In addition to a control simulation, ensembles of simulations were performed that included various combinations of changing radiative forcing, including those from natural sources (volcanic eruptions and solar irradiance changes) and anthropogenic sources (changes in greenhouse gases, aerosols, ozone, and land use changes).