CO₂ is garbage, not “plant food”.

It is recycled by photosynthesis using renewable solar energy.

From Eli. And it’s something with which I heartily agree! Plants do not `eat food`. If they did, they wouldn’t be plants. Moreover, any experiment where plants are exposed to an enriched CO₂ atmosphere in the absence of sunlight (or equivalent light) produces nothing. See below the figure for references on what happens to vegetation in an atmosphere with increased or variable CO₂ concentrations. Note that elevated Oxygen levels can also be toxic, not only for plants.

Two references:

• N. Devaraju, L. Cao, G. Bala, K. Caldeira, and R. Nemani, “A model investigation of vegetation-atmosphere interactions on a millennial timescale“, Biogeosciences, 2011, 8, 3677-3686.
• S. L. Thompson, B. Govindasamy, A. Mirin, K. Caldeira, C. Delire, J. Milovich, M. Wickett, D. Erickson, “Quantifying the effects of CO₂-fertilized vegetation on future global climate and carbon dynamics“, Geophysical Research Letters, 2004, , 31(L23211).