Some climbing cedar -- it's generating angry harangue (6)
I believe the answer is:
tirade
'angry harangue' is the definition.
(I've seen this before)
'some climbing cedar it's' is the wordplay.
'climbing' says the letters should be written in reverse (in a down clue, letters climb up).
'some' indicates a hidden word (some of the parts of the word are used).
'edarit' can be found hidden inside 'cedar its'.
'edarit' back-to-front is 'TIRADE'.
'generating' acts as a link.
(Other definitions for tirade that I've seen before include "Long speech of angry criticism" , "Long, abusive speech" , "Blast of criticism" , "Long angry piece of denunciation" , "Prolonged abusive speech" .)