The Jormungand Global Climate State and Implications for Neoproterozoic Glaciations

Geological and geochemical evidence can be interpreted as indicating strong hysteresis in global climate during the Neoproterozoic glacial events (~630 Ma and ?715 Ma). Standard climate theory only allows such strong hysteresis if global climate enters a fully-glaciated “Snowball” state. However, the survival of photosynthetic, eukaryotic, marine species through these glaciations may indicate that there were large areas of open ocean. A previously-proposed “Slushball” model for Neoproterozoic glaciations could easily explain the survival of these organisms because it has open ocean throughout the tropics, but there is only a small amount of hysteresis associated with the Slushball state. I will propose a new state of global climate, the Jormungand state, that is nearly, but not completely, ice-covered. I analyze this state using global climate models and the Budyko-Sellers model, and find that there is strong hysteresis associated with it as greenhouse gas levels are varied. This makes the Jormungand state a potential model for Neoproterozoic glaciations.