The coming ice age, whenever that happens, is linked to the increased conductivity of the atmosroughly 400phere and ocean due to increase CO2 and the orientation of the poles both with respect to solar irradiation and geomagnetic forcing. Big, bad and bold statement.
The polar oceans are the deep ocean thermostat. The only way that the deep oceans can gain or lose heat is by conduction. The only place on Earth for the deep oceans to lose heat is in the polar oceans. So my bold statement is not out of school, it has to be.
From a CO2 concentration of approximately 190 parts per million to roughly 400 parts per million, conductivity of the atmosphere increase by about 0.1 percent. Small potatoes on a century scale or less, but over thousands of years it adds up.
Polar orientation varies the rate of cooling of the deep ocean at the 4 C boundary because the Antarctic is a continent. When the geographical and geomagnetic poles are centered over the Antarctic land mass, less cooling is possible. Off centered orientation increase the area of the 4C boundary to atmosphere interface.
Without geomagnetic forcing, it is obvious that conductivity, polar orientation and the area of the 4C boundary of the ocean, the source of the down welling current that drives global climate, are the millennial scale drivers of glacial cooling. The question still is how much impact geomagnetic variability has on the mechanism.