Scratches carbon regulations (5)
I believe the answer is:
claws
'scratches' is the definition.
(clawing is a kind of scratching)
'carbon regulations' is the wordplay.
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'regulations' becomes 'laws' (I've seen this before).
'c'+'laws'='CLAWS'
(Other definitions for claws that I've seen before include "Talons" , "beastly offensive" , "Grasping limbs, of a crustacean, say" .)