A recent talk by Murry Salby has been widely hailed as a blockbuster, demolishing carbon cycle modeling, and proposing instead that rising temperature is responsible for the observed rise in atmospheric CO2.
Is this plausible? This video explores the possibilities with a very simple carbon cycle model.
The bottom line is "No."
This is a screencast using simulation software, and there's a lot of detail, so you'll want to view in HD (720p).