I have this vague feeling that this site is supported by the Australian Coal Mines Association, but what the heck. It provides some alternate explanations, so that we are not all going to die in Coke fumes!
I would suspect that there are very few places on earth where the availability of carbon dioxide is limiting growth. My fish tank is one, and greenhouses are the other. Most other places lack water, minerals, or nitrogen. Still, the Jurassic was high in carbon dioxide, and it enjoyed tremendous plant growth, even though I think it had a lot of water, as well. Age of the Dinosaurs anyone??