A less warm-hearted Maria (3)
I believe the answer is:
mia
'a less' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'warm-hearted maria' is the wordplay.
'warm' becomes 'summery'.
'hearted' indicates the central letters.
'maria' becomes 'ia' (I can't explain this - if you can you should believe this answer much more).
The central letter of 'summery' is 'm'.
'm'+'ia'='MIA'
(Other definitions for mia that I've seen before include "girl" , "- - Farrow, actress" .)