The higher Co2 goes, the warmer the planet gets as it warms permafrost melts, adding methane (also a greenhouse gas) as we warm, the atmosphere itself can hold more water vapor (also a greenhouse gas)
We know from previous natural glacial cycles that sea level rises and ice retreats, large glacial fields like Antarctica are slower to react but as they start to contribute to sea level rise the rate of rise goes up markedly.
As for Rasing Caines comment, sorry but as usual they are mostly fiction, this is a long term graph of Earths Co2 content
http://www.skepticalscience.com/images/Phanerozoic_CO2.gif
There is an initial drop in Co2 around the time life emerged onto land, Co2 didn't disappear it moved from the atmosphere to being locked up in biomass, millions of years of plants and soil, but then it rose through quite a long period then dropped again but with a number of spikes due to massive volcanic activity, there is little doubt we will see such activity again as the continents continue to move and crash into each other, but that may be 10's or 100's of million of years from now. Hardly relevant to what is happening here and now.
As for the drop of Co2 to 180ppm during the last glacial period, this at least is true, of course that was also true through at least the previous 7 glacial periods before that. Most likely it dropped that low through each glacial cycle going back to the start of the glacial cycles about 2.5 million years ago.
https://en.wikipedia.org/wiki/Glacial_period#/media/File:Co2_glacial_cycles_800k.png
Many plants died during these periods not because of lower Co2 but simply because the land itself was covered by ice and plants don't grow in ice. As deniers used to be so fond of telling us the ice extended down to New York so all the forests of Canada and Europe would have been under hundreds of meters of ice.
Through the last 800,000 years (and probably the last 2.5 million years) of glacial cycles Co2 has fluctuated between ~180ppm when glaciers rule and gone up to ~280ppm whan glaciers have retreated.
This is the low point in the above graph showing the long term history of Co2, yet now Co2 is up to just over 400ppm and at current rates of rise will be up to around 700ppm by the end of this century, the blink of an eye compared to the timescale of the graph above, this is about 2.5 times the low point of the graph above.
This graph show the last 400 thousand years in finer detail Co2 is the middle graph (in green)
https://en.wikipedia.org/wiki/Ice_core#/media/File:Vostok_Petit_data.svg
This graph shows the historic Co2 levels taken from ice cores, the graph stops at 300ppm, take it up to the current 400ppm and you would be well up into the graph above, take it up to the 700ppm likely by the end of this century and you are out of the total graph, entirely. in fact a level of 700ppm is a level not seen in perhaps 20-25 million years.
Current sea level rise estimates don't attribute much contribution from Antarctica as just 2% of Antarctica melting would add ~1m to sea level rise, and current estimates of sea level rise which use thermal expansion and contributions from both Greenland and Antarctica are for ~1m of sea level rise. But new work on the longer term effects of AGW out to 2500 suggest rises in sea level of up to 15m as Antarctic moves from being a small contributor to a major contributor.