How to start an ice age

Glaciations are neat - we're currently in one, and the subjects of my undergrad research lived in the previous one, the Late Paleozoic Icehouse. The Phanerozoic has seen three glaciations so far: the Ordovician Glaciation, the Late Paleozoic Icehouse, and the Cenozoic Ice Ages (glaciation, icehouse, and ice age are often used interchangeably). There were …