text: The reality is that, except in the most general terms, we are unable to satisfactorily explain past variations of climate. Over the recent 2 million years why did the primary mode of climate oscillation change from a 40,000 year (axial tilt) periodicity to one close to 100,000 years (linked to eccentricity)? And how do we explain the recent glacial cycles, given that annual solar insolation intercepted by the Earths disc changes little between near circular and more eccentric orbits? Even the relative regularity in value to which temperatures asymptote during each interglacial, as estimated from Antarctic ice cores, can hardly be attributed to chance yet does not have an explanation!