Planet Earth's becoming overheated — let's get leaders to retire (5)
I believe the answer is:
globe
'planet' is the definition.
(globe is a kind of planet)
'earth's becoming overheated let's get leaders to retire' is the wordplay.
'leaders' says to take the initial letters.
'to retire' says the letters should be written backwards.
The initial letters of 'earths becoming overheated lets get' is 'ebolg'.
'ebolg' reversed gives 'GLOBE'.
(Other definitions for globe that I've seen before include "London replica theatre" , "Planet Earth" , "Earth - sphere" , "Shakespeare's theatre" , "The round world" .)