Its always cold when worried farmer has job outside (10)
I believe the answer is:
permafrost
'its always cold' is the definition.
I can't judge whether this defines the answer.
'worried farmer has job outside' is the wordplay.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
'has job' becomes 'post' (I am not sure about this - if you are sure you should believe this answer much more).
'outside' means one lot of letters goes inside another (some letters go outside others).
'farmer' with letters rearranged gives 'ermafr'.
'ermafr' put into 'post' is 'PERMAFROST'.
'when' acts as a link.
Can you help me to learn more?
(Other definitions for permafrost that I've seen before include "Hard layer" , "Ground frozen for a long time" , "feature of polar regions" , "Ground never thawing" .)