The 41,000-year world
Global climate locks onto the tilt of Earth's axis, and glacial cycles begin keeping time.
- When
- —
- Duration
- 170 thousand years
- Known to
- ± 100 thousand years
- Era
- Pliocene, Cenozoic
Once large northern ice sheets exist, climate begins oscillating in step with the 41,000-year cycle in Earth's axial tilt, which controls how much summer sunlight reaches high latitudes. Deep-sea oxygen isotope records from this point on are a clean sawtooth at that frequency. It stays that way for over a million and a half years before shifting to the 100,000-year rhythm of the later Pleistocene — a change in the climate system's response, not in the orbital forcing itself, and still not fully explained.