Linda Sohl

Blast from the Past: Revisiting the Snowball Earth with GISS ModelE2

Between 750 and 635 million years ago, the Earth experienced two glacial intervals so severe 
that continent-sized ice sheets extended to within 10 degrees of the equator. The extreme glacial 
conditions were nicknamed "Snowball Earth," and in the popular media, the Earth of that time is 
often portrayed as looking like Jupiter's moon Europa today - i.e., completely covered in ice. But 
in the years since the term was popularized, geologists, paleobiologists and climate modelers 
have not been able to agree on whether the oceans froze over completely (the hard snowball 
scenario), or there were substantial areas of open ocean in the tropics (the slushball 
scenario). Our previous experiments using GISS Model II with a Qflux (mixed layer) ocean 
produced a slushball solution. However, Model II is an older coarse-resolution model without the 
latest physics and chemistry capabilities, and the Qflux ocean has prescribed ocean heat 
transports, so it has been unclear whether a more recent fully coupled ocean/atmosphere version 
of the GISS GCM would end up producing a hard snowball or a slushball.

In connection with a new effort underway at GISS to provide ModelE2-R with the flexibility to 
simulate climates of Earth's distant past as well as other Earth-like exoplanets, I will present 
some (very) preliminary results for a number of Snowball Earth-type sensitivity experiments, and 
talk about some of the challenges to be faced in planning and executing "otherworldly" climate 
simulations.