Late Ordovician glaciation under high atmospheric CO₂: A coupled model analysis

The analysis of the geologic record has revealed a question concerning how the Late Ordovician glaciation could have occurred simultaneously with high CO₂ levels (10–18x). Sensitivity studies using a coupled atmosphere-ocean-sea ice model show that it is possible to maintain a permanent snow cover (which corresponds to 60% of all the glacial deposits found on Gondwana) under 10x CO₂ levels, warm fall/cool spring orbital parameters, a 4.5% reduction in solar luminosity, a length of day of 21.5 hours, and an enhanced snow/sea ice albedo of 0.3. A cold summer orbit experiment with 10x CO₂ and a reduced snow/sea ice albedo of 0.1 also sustains a permanent (albeit less extensive) snow cover. The geographic configuration of the Late Ordovician results in an up to ∼42% increase in the global ocean poleward heat transport in the Southern Hemisphere relative to present-day and a significant asymmetry relative to the equator.