[nagant]

Look up Milankovitch cycles. The reason why we are in the mmidsdle of a 20,000 year interglacial is that we are in a period of the Milankovitch cycle with suffficient rotational axis tilt, where the orbital perihelion points the southern oceans at the sun during their summers. Southern oceans absorb far more heat than northern continents.

[Theophilus]

Thanks for the tip on Milankovitch cycles! The ideas seem intuitive.