CONDITIONS FOR THE INITIATION OF A NEOPROTEROZOIC SNOWBALL EARTH

The geologic record provides compelling evidence for episodes of global glaciation during the Neoproterozoic. Yet, the conditions necessary for instigating a snowball Earth remain unresolved. Climate modeling studies using GCMs have generated conflicting results, yet have generally underscored the extreme conditions required to initiate a snowball Earth. In our previous work with a coupled ocean-atmosphere model, we demonstrated that dynamic ocean processes prevent a snowball solution. Even in the case with a fully glaciated, tropical, idealized supercontinent, the simulated sea-ice equilibrium line rests at 28 degrees latitude due to sea-surface heating through convective mixing.

Here, we use the Fast Ocean-Atmosphere Model to investigate two factors, paleogeography and cloud properties, that may help explain our inability to simulate a snowball Earth. A comparison of model experiments using different idealized paleogeographies shows large differences in the simulated meridional oceanic heat transport, equilibrium sea-ice position, and global average temperature. These idealized experiments will be compared with a model run that includes a more realistic Neoproterozoic paleogeography. In our Neoproterozoic simulations, cloud radiative forcing serves as a negative feedback on sea-ice growth. However, the GCM cloud properties have not been optimized to reflect the clouds that develop in arctic regions. The sensitivity of the Neoproterozoic climate to reasonable changes in the cloud properties will be presented.