Greek character turning up in temperate zones (4)
I believe the answer is:
zeta
'greek character' is the definition.
(letter from the Greek alphabet)
'turning up in temperate zones' is the wordplay.
'turning up' says the letters should be written in reverse.
'in' says the answer is hidden in the clue.
'atez' is hidden in the letters of 'temperate zones'.
'atez' reversed gives 'ZETA'.
(Other definitions for zeta that I've seen before include "Greek letter Z" , "Welsh actress, Catherine __-Jones, b. 1969" , "Sixth letter of the Greek alphabet" , "Letter to the Corinthians" , "Foreign character" .)