CO2 is not a bad thing, I don't know why so many of you are concerned with a single trace element. .
Co2 is an important part of the natural carbon cycle. But since the industrial revolution we have dug up and burnt carbon that was effectivley taken out of the earths natural carbon cycle (fossil fuels) and put into the atmosphere, where we know it traps the suns energy (greenhouse gas). We have near on doubled the concentration of co2 in the atmosphere, causing the earth to warm.