The recovery of higher-resolution ice cores spanning more of the past 1,000,000 years by the ongoing EPICA project may help shed more light on the matter. A new, high-precision dating method developed by the team allows better correlation of the various factors involved and puts the ice core chronologies on a stronger temporal footing, endorsing the traditional Milankovitch hypothesis, that climate variations are controlled by insolation in the northern hemisphere. The new chronology is inconsistent with the "inclination" theory of the 100,000-year cycle. The establishment of leads and lags against different orbital forcing components with this method—which uses the direct insolation control over nitrogen-oxygen ratios in ice core bubbles—is in principle a great improvement in the temporal resolution of these records and another significant validation of the Milankovitch hypothesis. An international climate modelling exercise (Abe-ouchi et al., Nature, 2013) demonstrated that climate models can replicate the 100,000-year cyclicity given the orbital forcing and carbon dioxide levels of the late Pleistocene. The isostatic history of ice sheets was implicated in mediating the 100,000-year response to the orbital forcing. Larger ice sheets are lower in elevation because they depress the continental crust upon which they sit, and are therefore more vulnerable to melting.
