This is the reason you should dress for the weather enroute and not just the weather in the terminal(s). The polar flights I've been on have been cold inside the aircraft. If you need an excuse, use the cold cabin temps to justify dressing warmly. Wool is good for air travel -- warm when it's cold, cool when it's hot, much safer if there's a fire or if you need to evacuate the aircraft and leave everything behind.

It doesn't even need to be a polar flight. A flight I was on while flying home for Christmas had to land in Minot ND for fuel -- much colder there than at either end of the flight.