Very hot temperature, almost all polar ice melted (8)
I believe the answer is:
tropical
'very hot' is the definition.
(in the tropics)
'temperature almost all polar ice melted' is the wordplay.
'temperature' becomes 't' (abbreviation).
'almost all' means to remove the last letter.
'melted' indicates anagramming the letters.
'polar'+'ice'='polarice'
'polarice' with its final letter removed is 'polaric'.
'polaric' anagrammed gives 'ropical'.
't'+'ropical'='TROPICAL'
(Other definitions for tropical that I've seen before include "Hot and humid, near the equator" , "April-Oct, unusually humid and very hot" , "Hot and humid type of weather" , "Originating from hotter parts of the earth" , "Fervidly hot" .)