Milankovitch forcing in paleoclimate data

This study addresses the strength of the statistical relationship between paleoclimate data and the Earth orbital forcing. A methodology called the nonparametric additive model (NPAM) was used to relate δ18O data of the North Greenland Ice Core Project (NGRIP) ice core and reconstructed temperatures of the Vostok ice core to eccentricity, obliquity, and precession. Both data sets depended linearly on precession and approximately linearly on obliquity, but relations to eccentricity had more complex forms. Percentage variance reductions obtained by these 3 Earth orbital parameters were almost identical for the 122 950 yr NGRIP data and the 422 766 yr Vostok data. Specifically, variance explained by eccentricity was 40.2 ± 3% and 36.6 ± 1.7% of the variance of NGRIP and Vostok data, respectively. The contributions of obliquity and precession to the variance were 27.9 ± 3% and 31.1 ± 1.7% for the 2 data sets.