Actually GF you are right. The time in earth's biological history with the greatest diversification of plant and animal life, as well as gigantic life forms, came during an era when CO2 was considerably higher (on the order of multiple times higher) than the current levels of CO2. Right now global CO2 concentrations are under 400 ppm. In the Jurassic the CO2 levels were 1800 ppm. Turns out that the very heavy volcanic at that time could spew out far more CO2 than we can produce now. Who knew?
In fact this, our current, era of earth history has one of the lowest concentrations of atmospheric CO2 and is overall one of the coolest epochs in earth's geological history. There are also theories that there is an upper limit to the heating effect of CO2, that after it passes a certain concentration temperature rises at a decreasing rate and then levels off.
There was even a time when an ice age coincided with far higher concentrations of CO2 than we experience today (the late Ordovician period with CO2 approaching 4000 ppm). This actually represented a drop-off of nearly half the CO2 (from 7000 ppm to around 4000 ppm) concentration just before and caused an ice-age. All at well over 10 times the CO2 we are experiencing today.
By 2025 we'll be trying to figure out a way to heat the Earth. CO2 won't be quite so evil any longer.
