A snowball Earth versus a slushball Earth: Results from Neoproterozoic climate modeling sensitivity experiments Micheels and Montenari (2008) By: Madeline Gentry, ESS 433

Snowball Earth Glaciation was found to be incredibly widespread in Neoproterozoic Paleomagnetic evidence found glaciation advanced into equatorial latitudes Scientists proposed the earth was actually entirely glaciated This is the “Snowball Earth” theory

Or was it? Not all scientists agree that the Earth was completely frozen “slushball” Earth as opposed to “snowball” proposed as more likely scenario

Snowball vs. Slushball Many atmosphere and climate models were created to test the theories However, results even within the same studies contradict constantly Reasons for contradictions and shortcomings of models unclear Micheels and Montenari set out to test sensitivity of models and viability of snowball vs slushball

Neoproterozoic Sensitivity Experiments Earth system model of intermediary complexity (EMIC) was used Core module is PUMA-2, the simple atmospheric general circulation model Combines slab ocean and thermodynamic sea ice model Model accounts for physical processes such as radiation transfer, cloud formation, and large scale precipitation Ocean circulation not accounted for, but heat exchange between atmosphere and ocean is

Paleogeography and Paleo-orography Model Paleogeography: Breakup of Rodinia began the transition into the Neoproterozoic glaciation Super continent must be positioned in lower latitudes to allow for extreme glaciation Paleo-orography: Elevation of mountains set to be ~1000m and interior land mass~50 m Paleo-orography found to have little effect on debate

Other Model Parameters Land surface cover Glacier (NEO-2 to NEO-4) vs. Desert environments (NEO-1 & 5) CO2 Levels 510 ppm used for NEO 1-5, the best estimate for Proterozoic levels 280 ppm used for second run of NEO through Initial ocean conditions Cold Ocean (271 K) (NEO 1-2) vs Cool ocean ( K) (NEO 3-5) NEO 1-2 model Snowball Earth, while the others model Slushball Earth

Results- Temperature and Ice depth All show temperatures below freezing Only NEO 1-2 show temps consistent with total ice coverage Ice Thickness consistent for Snowball (~1km) for Neo 1-3

Results- CO2 Lower CO2 levels lead to lower temperature, but ice cover doesn’t change significantly

Land Surface Cover- Results Desert simulations (NEO 1 and NEO 5) have lower albedo (.35) and therefore warmer conditions than comparable runs Desert condition is ~14 degree warmer Indicates formation of glaciers lead to a positive feedback loop

Spatial Temperature Patterns and Sea Ice Margins

Zonal Averages of Mean Annual Temperature

Hydrological Cycle and the Fossil Record Other experiments found active hydrological cycle between paleolatitudes 30° and 40° (e.g., Christie-Blick et al., 1999; Leather et al., 2002) This matches better with slushball models that have sea ice margin at around 15° Fossil records also show no massive extinction, which a snowball Earth would necessitate A slight increase of synglacial microbiota was found (Corsetti et al., 2003)

Weak Points The model leaves out some real world influences such as ocean currents Paleogeography and paleo-orography also not certain However past studies prove these would affect results in non significant ways (Romanova et al., 2006)

Conclusion Only Neo-1 and Neo-2 support the theory of Snowball Earth These models assume initial global glaciation however, so are not extremely realistic Models with less forcing all indicate slushball Earth conditions, with a majority of earth covered in ice but not al