This is pathetic. In my high school biology course back in the 50s we learned about the CO2-O2 cycle, with animals needing oxygen and plants needing carbon dioxide. This is, we were taught, a self-balancing cycle, since if it tilts one way or the other it encourages more animals or plants, bringing it back into balance. Much of the work, of course, is done by small animals and plants—bacteria, insects, plankton, and the like, that can grow pretty quickly.
I always thought that a good counter-charge to make against these whacko greenies is that by decreasing CO2 they are killing the rain forests. Which, in fact, they are doing, with their biofuel idiocies.
The idiot global warming fanatics might be surprised to hear that trees are made of cellulose -(C6 H10 O5), the carbon coming from, of course, atmospheric CO2.