Cold — 0 and below! (8)
I believe the answer is:
loveless
'cold' is the definition.
(both can mean uncaring)
'0 and below' is the wordplay.
'0' becomes 'love' (a score of zero is love in tennis).
'and' is a charade indicator (letters next to each other).
'below' becomes 'less' (below a certain amount).
'love'+'less'='LOVELESS'
(Other definitions for loveless that I've seen before include "without heart" , "Cold-hearted" , "Without affection" .)