Equilibrium temperatures are found for several hypothetical atmospheres with large water vapor concentrations (vapor pressure from 50 mb to 1013 mb) at stratospheric levels. Radiative equilibrium is computed using the Air Force radiation algorithm LOWTRAN 7 with no clouds or aerosols. The initial starting condition of an isothermal atmosphere at about -100°C warms to over +100°C at the base of the water vapor layer and becomes isothermal to the surface within 1 to 2 years. Temperatures are sufficiently warm to maintain large quantities of water in vapor form but are too hot for the surface to be habitable. The temperature and pressure in the highest levels are such that cirrus clouds will form. These clouds would reflect a large portion of incoming solar radiation, thereby likely altering atmospheric stability and surface temperature.