Such temperatures are cold to bear (5)
I believe the answer is:
polar
'bear' is the definition.
(polar bear is a kind of bear)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for polar that I've seen before include "Relating to the Arctic or Antarctic" , "Of the far north or south" , "Extremely cold region" , "Of the cold regions" , "extremes of 3 or 26 [NORTH OR SOUTH]" .)