Throughout the past three million years, variability in the oxygen-isotopic composition of the ocean, caused by changing ice-sheet mass on the continents, has been concentrated at the frequencies associated with changes in the earth's orbital geometry. The amplitude of variability has increased towards the present. An increase in variability associated with changes in the obliquity of the Earth's rotational axis (period 41 ka) during the early Pleistocene was followed by an increase in power related to the precession cycle (23 ka) and associated ellipticity cycle (ca. 100 ka) during the past million years. Although deep-sea sediments are the best place to observe this evolution in climatic variability, we will not be able to understand it without more data from other geological sources.