Theory 73/Glacial cycle/Onset phase
Glaciation Starts on a Summer Threshold
The claim
A glacial cycle begins when summer insolation falls below a threshold set by the ratio of ablation to accumulation, so the same orbital forcing acts differently at different latitudes.
01Mechanism
Ice survives if summer melt is less than winter accumulation; the ratio sets the threshold.
02Prediction
Onset should track the ratio.
03Refutation
Onset tracking global temperature would remove insolation geometry.