Fierce changes involving climate, ultimately - how’s the Arctic in summer? (3-4)
I believe the answer is:
ice-free
'how's the arctic in summer?' is the definition.
(arctic ice increasingly melts in the summer)
'fierce changes involving climate ultimately' is the wordplay.
'changes' indicates an anagram.
'involving' is an insertion indicator.
'ultimately' suggests the final letters.
The final letter of 'climate' is 'e'.
'fierce' anagrammed gives 'icefre'.
'icefre' placed around 'e' is 'ICE-FREE'.
(Other definitions for ice-free that I've seen before include "Like much of the Arctic in summer" , "(Of water) not frozen" .)