Excess of permanent ice melting (12)
I believe the answer is:
intemperance
'excess' is the definition.
(I've seen this before)
'permanent ice melting' is the wordplay.
'melting' is an anagram indicator.
'permanent'+'ice'='permanentice'
'permanentice' is an anagram of 'INTEMPERANCE'.
'of' acts as a link.
(Other definitions for intemperance that I've seen before include "bingeing" , "Unrestrained alcohol consumption" , "lack of restraint" , "excess drunkenness?" .)