The NCAR Climate System Model, version one, is described. The spinup procedure prior to a fully coupled integration is discussed. The fully coupled model has been run for 300 yr with no surface flux corrections in momentum, heat, or freshwater. There is virtually no trend in the surface temperatures over the 300 yr, although there are significant trends in other model fields, especially in the deep ocean. The reasons for the successful integration with no surface temperature trend are discussed.