Sure, we know the answer is "The world is getting hotter and it's all our fault" - but there are still a heck of a lot of questions that need to be answered. "How Fast?" and "Will the extra CO2 help crops or weeds grow faster?" and "What can we do about it?" and "Will such-and-such course of action have enough effect to avoid such-and-such consequences?"
We need those guys even more than we did before the original question was answered.
One question was addressed many (I think about 25) years ago, at least on a small scale.
Some scientists saturated a field with CO2 for several months to observe the effects. (Thus, contributing to global climate change :) )
What they found was that the plants grew significantly larger, but they were also much less nutritious. This, in turn, led to bugs having to eat more plants.