In order to carry out a study of the origins and thermodynamic mechanisms of the large-scale climate oscillations and glaciations of the earth which have occurred over the last few hundred thousand years, a simplified thermodynamic model of the glaciers-ocean-atmosphere global system is constructed. The dynamics of the system are analyzed by computer, and the perturbations due to deviations of the earth's orbit and to tectonic forces are examined. The characteristic regimes of the system are auto-oscillations, which exist with realistic numerical values of all parameters. Auto-oscillations occur in the northern hemisphere owing to nonlinear interactions between two large inertial components which are determined by the heat capacity of the ocean and mass accumulation in continental ice sheets. The southern hemisphere represents an aperiodic system where oscillations are induced and occur on account of energy and mass transfer across the equator. The periods of calculated auto-oscillations vary from 20,000 to 80,000 years. The length of climatic waves generated in the presence of external disturbances exceeds the auto-oscillation period of the model. These results are in good agreement with paleoclimatic reconstruction data. The calculated variations in the mean temperature of both hemispheres, the temperature differences between the equator and pole, the sizes of marine and continental ice covers, the ocean level, and other values are of the same order of magnitude as those of empirical data. The transition from a relatively warm epoch (when continental ice sheets are absent) to conditions characteristic of the Pleistocene is modeled. The calculated curves show how weak temperature fluctuations are succeeded by large-scale oscillations. Thus the simulation results not only provide an answer to the question concerning the cause of oscillations in the earth's climate and glaciation during cold epochs, but they also explain the absence of oscillations during warm epochs; in the absence of the second inertial link (continental ice) the system is essentially aperiodic.