The intensification of glaciation in the Mid‐Pliocene and the Earth's obliquity variation

The intensification of glaciation in the northern hemisphere during the past 3 Myr has clearly been confirmed by δ 18 O record for deep‐sea sediment cores extending over the past 5–6 Myr. For earth models with a lower mantle viscosity of greater than 10 22 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.