I think what needs to be questioned is this...

We actually live in CO2-starved condition right now. Doubling or trippling the amout of atmospheric CO2 would lead to an increase in plant growth and a greater abundance of food." pdq

It is the first time on my life I have ever seen this claim. It is my understanding that plant thrive with enough water and nutrients in the soil. That is certainly true for our garden. I see farmers fertilizing and irrigating. When was the last time you saw one dumping dry ice on a garden? I drive by fossil fuel power plants several times a year, I don't notice the vegetation near the plants as being more abundant. I do notice more plants where there is more water. Have you ever driven from San Antonio to New Orleans? If you did you would know what I mean.