Why do refrigerators use more energy when an accumulation of ice is present in the Freezer?

Question

i.e. when the refrigerator is not defrosted

Answer 1

ice is an insulator and it prevents the Freezer from efficiently cooling itself.

Answer 2

Because the accumulation of ice, blocks the airways for the freezer to cool the rest of the refrigerator. So it has to work harder to circulate cold air. Sometimes the accumulation can stop the fan itself.

Answer 3

Its global freezing, what have we got to teach you everything?