The role of the oceans in the formation of the earth's climate is discussed. A simple model for global air-sea interaction is proposed which takes into account the latitudinal variation of the planet's radiation budget, atmospheric sensible and latent heat transport due to baroclinic instability of zonal flow, and heat transport by ocean currents. The model permits assessment of the characteristics of climate (global temperature differences and meridional heat fluxes in the atmosphere and ocean, mean temperatures at the poles and equator, typical wind velocities, etc.) using the astronomical parameters of the planet and basic information about its atmosphere and ocean. The model was used to compare the variants of the earth's present climate and that of the Mesozoic era (on the assumption that both poles were located in the open ocean) and to determine the climatic effect of a possible variation in the earth's rate of rotation. The estimates indicate a pronounced weakening of the temperature zonality and indicate, in particular, the absence of polar glaciers in the Mesozoic era.