Copy infantry photo: how much one adds to the atmosphere! (6,9)
I believe the answer is:
carbon footprint
'how much one adds to the atmosphere' is the definition.
(amount of CO2 a person is responsible for)
'copy infantry photo' is the wordplay.
'copy' becomes 'carbon' (as in a carbon copy).
'infantry' becomes 'foot' (I've seen this before).
'photo' becomes 'print' (as in a print of a photograph).
'carbon'+'foot'+'print'='CARBON FOOTPRINT'
(Other definitions for carbon footprint that I've seen before include "From measure of energy usage" , "emissions" , "emission level" , "personal effects?" .)