Learnt Arctic can be obstinate in opposition (12)
I believe the answer is:
recalcitrant
'obstinate in opposition' is the definition.
(I've seen this before)
'learnt arctic can be' is the wordplay.
'can be' is an anagram indicator.
'learnt'+'arctic'='learntarctic'
'learntarctic' is an anagram of 'RECALCITRANT'.
(Other definitions for recalcitrant that I've seen before include "Obstinate in opposition" , "Not willing to accept discipline" , "Wilfully disobedient" , "Refractory" , "Defiant" .)