The Milankovitch cycles[1] almost certainly play a significant role. The arrangement of the continents also has a huge effect on climate, because an Earth with

The Milankovitch cycles[1] almost certainly play a significant role. The arrangement of the continents also has a huge effect on climate, because an Earth with only one large ocean transfers heat much differently than one with two major oceans. It's largely because of the positions of the continents, including a large polar continent, that we are still in an ice age[2]. However an event like a massive volcanic discharge could conceivably start a positive feedback loop of cooling. Since ice has a high albedo, we could get a runaway, well, snowball effect. [1] https://en.wikipedia.org/wiki/Milankovitch_cycles https://en.wikipedia.org/wiki/Milankovitch_cycles [2] https://en.wikipedia.org/wiki/Quaternary https://en.wikipedia.org/wiki/Quaternary