Clouds and Snowball Earth deglaciation

Neoproterozoic, and possibly Paleoproterozoic, glaciations represent the most extreme climate events in post- Hadean Earth, and may link closely with the evolution of the atmosphere and life. According to the Snowball Earth hypothesis, the entire ocean was covered with ice during these events for a few million years, during which time volcanic CO₂ increased enough to cause deglaciation. Geochemical proxy data and model calculations suggest that the maximum CO₂ was 0.01-0.1 by volume, but early climate modeling suggested that deglaciation was not possible at CO₂ = 0.2. We use results from six different general circulation models (GCMs) to show that clouds could warm a Snowball enough to reduce the CO₂ required for deglaciation by a factor of 10-100. Although more work is required to rigorously validate cloud schemes in Snowball-like conditions, our results suggest that Snowball deglaciation is consistent with observations.