Yes, there was a lot more CO2 in our atmosphere for most of Earth's history in comparison to today levels. For last few millions years, earth's CO2 levels were extremely low. Today's current levels are very low- if you were double the current amount of CO2 in the atmosphere you would get a slight increase in average global temperature. If you were to increase the levels by 10 times the current level you would still have low levels of CO2 in comparsion to most of Earth history. If you were to increase the amount of CO2 by factor of hundred you might get more than 10 degree in temperature increase in global average temperature- but more importantly, humans and other animals couldn't breathe very easily- though the plants would be very happy to get more CO2.