Matt, this professor is a P chem guy and really nails it on the head when it comes to CO2's interaction with photons. His very last point in this post is perfect. 

"Comparing the two the wavelength of the photon is about 330 times larger than the average spacing between CO2 molecules in air. 

Not every CO2 molecule is going to absorb that photon, but there are an awful lot of CO2 molecules that can.

On average a 15 micron photon at the surface will travel a couple of meters before it is absorbed"

http://rabett.blogspot.com/2016/04/its-number-density-not-mixing-ratio.html