Deep-sea sediment records suggest Northern Hemisphere glaciation intensified at approximately 2.75 Ma. In this paper we simulate the fluctuations of the late Pliocene Northern Hemisphere ice-sheets volume using the LLN 2-D model, forced by the astronomically derived insolation and by scenarios of CO2 concentrations. The model simulates the waxing and waning of the Northern Hemisphere ice volume in an acceptable agreement with geological reconstructions, and in particular supports the geological evidence that the development of significant Northern Hemisphere ice sheets started between 2.75 and 2.55 Ma, a time interval accompanied by quite high and stable eccentricity values, and increased obliquity amplitude. When the CO2 concentration is lower than a threshold value, the Milankovitch forcing explains the suddenness and specific timing of this entrance into the Ice Age during the late Pliocene.