Protests over British planes storing up carbon (7)
I believe the answer is:
objects
'protests' is the definition.
(I've seen this in another clue)
'over british planes storing up carbon' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'planes' becomes 'jets' (jet is a kind of plane).
'storing up' indicates putting letters inside.
'carbon' becomes 'C' (chemical symbol).
'jets' placed around 'c' is 'jects'.
'o'+'b'+'jects'='OBJECTS'
(Other definitions for objects that I've seen before include "Takes exception to the things?" , "Material things" , "Articles; aims" , "Expresses opposition" , "Opposes" .)