Ice Age Relaxation Oscillator
An Ice age takes about 10 times longer to build up, than to drop off. Most proposals suggest that the cycle is triggered by carbon dioxide, planetary perbubations, and so on. A more traditional method, even in nuclear physics, is to calculate mass with a spring constant; and then, to predicate the period.
For this model, the trigger is the geology which is not constant over millions of years. For the last million years the resonant feature or Q-measurement would be the Missisippi river.
If the earth "suddenly" heated up, the steam would simply build up the ice fields at the highest altitudes and lattitudes. Cloud cover typically blocks 90% of the heat radiation coming in. Finally, hurricanes transport enormous amounts of heat to the upper atmosphere.
On the other hand; if vast quantities of cold water flowed into the Gulf of Mexico, cloud formation is inhibited. The average solar radiation of around 1,000 watts per meter converts the glaciers to water in a few thousand years.