Quantitative estimate of the Milankovitch-forced contribution to observed Quaternary climate change

A number of records commonly described as showing control of climate change by Milankovitch insolation forcing are reexamined. The fraction of the record variance attributable to orbital changes never exceeds 20%. In no case, including a tuned core, do these forcing bands explain the overall behavior of the records. At zero order, all records are consistent with stochastic models of varying complexity with a small superimposed Milankovitch response, mainly in the obliquity band. Evidence cited to support the hypothesis that the 100 Ka glacial/interglacial cycles are controlled by the quasi-periodic insolation forcing is likely indistinguishable from chance, given the small sample size and near-integer ratios of 100 Ka to the precessional periods. At the least, the stochastic background ‘‘noise’’ is likely to be of importance. r 2004 Elsevier Ltd. All rights reserved.