The carbon dioxide levels necessary to unfreeze the Earth have been estimated as being 350 times what they are today, about thirteen percent of the atmosphere.[40] Since the Earth was almost completely covered with ice, carbon dioxide could not be withdrawn from the atmosphere by the weathering of siliceous rocks. Over 4 to 30 million years, enough CO2 and methane, mainly emitted by volcanoes, would accumulate to finally cause enough greenhouse effect to make surface ice melt in the tropics until a band of permanently ice-free land and water developed;[41] this would be darker than the ice, and thus absorb more energy from the sun — initiating a "positive feedback." http://en.wikipedia.org/wiki/Snowball_Earth#Breaking_out_of_global_glaciation
So yes, it was mostly CO2 that warmed the earth up but at 350 TIMES current levels. So current CO2 levels effect on current global warming trends(more specificly man made contributions being just a fraction of the current CO2 levels) has nothing to do with the levels that brought the earth out of the great snowball period. 13 percent back then verus .03 percent today. Apples and oranges my friend, apples and oranges.
And if you are wondering where that 13 percent CO2 went, well it got absorbed by the oceans, and plant life, and turned into things like limestone by lil tiny ocean critters. More to the point the earth absorbed it, which is its natural tendency to do. Yet another reason to believe that humans can’t do irreparable damage to this wonderful, ever resilient planet.
jim s