CLIMATE × EARTH

Antarctica Freezes

~34 million years ago

Phanerozoic · Cenozoic · Paleogene · Eocene

Carbon dioxide fell below the level at which ice can survive an Antarctic summer, and an ice sheet spread across the continent in about five hundred thousand years. The world tipped from a greenhouse with no permanent ice into the icehouse we still live in.

Why it matters

Everything since happens on a planet with one pole already locked up. Every ice age our own species evolved through is a swing inside that state, not a change of state, and the threshold that was crossed here is the one the carbon we are releasing is pushing back towards.

Dating & uncertainty

The transition took about 500,000 years and is read from oxygen isotopes, which mix ice volume with temperature. Falling carbon dioxide fits the evidence better than the opening of ocean gateways, but the orbit set the exact moment.

Sources

1. Hutchinson et al. (2021), Climate of the Past · The Eocene-Oligocene transition: a review of proxy data, models and comparisons
2. Ladant et al. (2014), Paleoceanography · The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition
3. Lisiecki & Raymo (2005), Paleoceanography · A Pliocene-Pleistocene stack of 57 globally distributed benthic oxygen isotope records

Earth history as one day

23:49:1210 min 47 s before midnight

if Earth’s 4.54 billion years were compressed into a single day