The climate modeling program at GISS is primarily aimed at the development of coupled atmosphere-ocean models for simulating Earth's climate system. Primary emphasis is placed on investigation of climate sensitivity --globally and regionally--including the climate system's response to diverse forcings such as solar variability, volcanoes, anthropogenic and natural emissions of greenhouse gases and aerosols and paleo-climate changes. A major focus of GISS GCM simulations is to study the human impact on the climate as well as the effects of a changing climate on society and the environment. The GISS GCM is prominently featured in the Intergovernmental Panel on Climate Change (IPCC) reports (the upcoming AR5 as well as past reports), and over 50 TB of climate model results have been publicly archived for the 5th Coupled Model Intercomparison Project. This project has included simulations for the historic period, future simulations out to 2300, and past simulations for the last 1,000 years, the last glacial maximum and the mid-Holocene.