ScienceDaily (Dec. 1, 2011) — A drop in carbon dioxide appears to be the driving force that led to the Antarctic ice sheet's formation, according to a recent study led by scientists at Yale and Purdue universities of molecules from ancient algae found in deep-sea core samples. The team pinpointed a threshold for low levels of carbon dioxide below which an ice sheet forms in the South Pole, but how much the greenhouse gas must increase before the ice sheet melts -- which is the relevant question for the future -- remains a mystery.
http://www.sciencedaily.com/releases/2011/12/111201174225.htm