I start to complain and step back: it’s very cold (3,3)
I believe the answer is:
'it's very cold' is the definition.
(ice caps are cold)
'i start to complain and step back' is the wordplay.
'start to' says to take the initial letters.
'and' is a charade indicator (letters next to each other).
'step' becomes 'pace' (synonyms).
'back' is a reversal indicator.
The initial letter of 'complain' is 'c'.
'pace' backwards is 'ecap'.
(Other definitions for ice cap that I've seen before include "Cold mass permanently covering the polar regions or mountain peaks" , "Permanently frozen mountain-top mass" , "Frozen polar region" , "mountain peak, perhaps?" , "Polar feature" .)