UN climate blunders come to a head (9)
I believe the answer is:
culminate
'a head' is the definition.
(thesaurus)
'un climate blunders' is the wordplay.
'blunders' indicates an anagram.
'un'+'climate'='unclimate'
'unclimate' anagrammed gives 'CULMINATE'.
'come to' acts as a link.
(Other definitions for culminate that I've seen before include "Wind up" , "Bring to high point" , "Come to a climax (in)" , "Reach a climax" , "End" .)