Common sense says that increases of CO2 lead to increased total plant mass. The phenomenon that occurs is call "Natural Carbon Sequestration". Pointy headed group thinkers keep saying yes, but...
There is no need for the but. The more CO2 produced, the more plants are fed and fertilized, fifth grade science, end of story. The but in this particular case is yet another instance of common sense falling victim to pointy headed logic (that my made up reason has to be better than traditional thought). "The effect of temperature is mostly negative"! This guy would try to grow green beans in Antarctica just to show that his ideas are "smart"!
"doubling that amount of carbon dioxide while holding steady all other inputs–water, nutrients, and so forth–yields a 70 percent increase in plant growth, an obvious boon to agricultural productivity.” I’m not 100% sure of this, but"
- Climate change in Superfreakonomics | Stand-Up Economist (view on Google Sidewiki)