Figure 4.

Archean sea ice cover versus pCO₂. The colored lines in each panel correspond to salinities of 20 (blue), 35 (green), and 50 g/kg (yellow). Four distinct climate states that are separated by abrupt transitions emerge for the CO₂ range considered. The CO₂ threshold for the transition between these states is sensitive to ocean salinity, allowing small changes in salinity to profoundly change climate. For example, at 100 xPIL CO₂, global average surface temperature differs by 45°C between the 20 and 50 g/kg salinity scenarios. All simulations were initiated from an ice‐free state.