Ever hear of the H.A.B. theory?
In short, since the poles are always sub-freezing and therefore precipitation never melts, it accumulates.
Since the Earth rotates on an axis that is not perpendicular to the Sun, every 15,000 or so years the Earth "wobbles" onto it's side (like top).
So almost instantiously, the poles are moved to the equator and the equator becomes the poles.
H.A.B. theory - Have Another Beer? I belive I will!