Carbon dioxide settles into the icehouse range
Atmospheric CO2 drops from Eocene greenhouse values toward levels the modern world would recognise.
- When
- —
- Duration
- 11 million years
- Known to
- ± 2 million years
- Era
- Oligocene, Cenozoic
Proxy reconstructions put Oligocene atmospheric carbon dioxide in the range of roughly 400 to 700 parts per million, well below the 1,000-plus of the early Eocene. The drawdown is attributed to some combination of Himalayan uplift accelerating silicate weathering, organic burial, and reduced volcanic outgassing. This is the level at which a permanent Antarctic ice sheet becomes possible but a northern one does not — which is why the Oligocene has ice at one pole only, and why the threshold matters so much to projections of the present.