That is a 3rd grade level oversimplification of the phenomenon. According to that graph, there should be an "atmospheric mirror" at a very specific altitude that bounces back "heat".
That's not what's happening. The infrared radiation is scattered and deflected IN ALL DIRECTIONS by CO2 molecules. If there were less CO2 molecules, less heat would be deflected back to the surface, and more heat would escape the gravity well.
Again, I'm over-simplifying, but please, for the love of $DEITY, do not take these graphs as a realistic depiction of what's going on. It's for illustration purposes only.