Last of air removed from high cloud and carbon injected as entertainment (6)
I believe the answer is:
circus
'entertainment' is the definition.
(circus is a kind of entertainment)
I don't understand the rest of the clue.
(Other definitions for circus that I've seen before include "Roundabout for the animal acts" , "entertaining show" , "'Travelling company of clowns, acrobats etc (6)'" , "tented area" , "Roman sporting arena" .)