Greenhouses require light and in the gloom following a pole shift it won't be available. Actually, your thoughts make me think about a hybrid approach. Picture an indoor area within a dome with full spectrum lights (halide is most efficient) and plants growing in greenhouses beneath. What greenhouses do is concentrate the light generating heat, instead of letting it out. If you had a place with 25 foot ceilings, greenhouses would help keep the heat in. 10 foot ceilings or less, why bother?!
Offered by John.