The Mi-1 glaciation
A sharp return of the ice at the Oligocene-Miocene boundary, timed by a rare orbital coincidence.
- When
- Known to
- ± 100 thousand years
- Era
- Miocene, Cenozoic
At about 23 million years ago the warming reverses abruptly and Antarctic ice expands again in the event labelled Mi-1. Its trigger is unusually well identified: a coincidence of low orbital eccentricity with a node in the obliquity cycle produces an extended run of cool, low-variance southern summers — exactly the conditions for ice to survive the melt season. The event defines the base of the Miocene, and it is one of the cleanest demonstrations anywhere that orbital geometry can force a global climate state change.