This two year project is an evaluation, comparison and diagnosis of the high-latitude performance of four climate models that have been used in CO2-sensitivity experiments. Systematic departures of primary atmospheric variables (e.g temperature, pressure, etc.) from observed distributions will be assessed in context of CO2 sensitivity experiments. These departures will be diagnosed in terms of the model physics, and the differences in the model's fidelity to the present climate will be used to assess the importance of various physical processes in the high- latitude climate system. This study is of fundamental importance because it promises to lead to improvements of GCMs in the treatment and understanding of Polar climate.