Observe increasing feature of Arctic after time taken into account (6)
I believe the answer is:
notice
'observe' is the definition.
(noticing is a kind of observing)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for notice that I've seen before include "Spot - review" , "Review - poster" , "See; advert" , "Public announcement" , "Remark upon; small advertisement" .)