The intensification of glaciation in the northern hemisphere during the past 3 Myr has clearly been confirmed by Δ 18O record for deep-sea sediment cores extending over the past 5--6 Myr. For earth models with a lower mantle viscosity of greater than 1022 Pa s inferred from several geophysical observables, perturbations in the Earth's dynamic ellipticity in response to this long term climatic change might have produced an increase of the average Earth's obliquity 0.06¿ through the resonant effect associated with the orbits of Jupiter and Saturn. This predicted obliquity change may consequently operate as a negative feedback on solar insolation, resulting in a reduction of the intensification of glaciation. ¿ 1998 American Geophysical Union