Burning coal ends in climate doom, bishop fears occasionally (5)
I believe the answer is:
ember
'burning coal' is the definition.
(I've seen this before)
'ends in climate doom bishop fears occasionally' is the wordplay.
'ends in' suggests the final letters (I've seen 'end in' mean this).
'bishop' becomes 'b' (abbreviation used in chess).
'occasionally' means one should take alternating letters.
The final letters of 'climate doom' are 'em'.
The alternate letters of 'fears' are 'er'.
'em'+'b'+'er'='EMBER'
(Other definitions for ember that I've seen before include "Remnant of bonfire" , "Piece of live coal" , "Material in dying fire" , "Smouldering piece left over from a fire" , "something that glows" .)