It is a detail, but, don't you think is it weird to have polar city with many solar farm ? in polar region, solar energy should be really low because there not much solar insolation (it is precisely the reason why it is so cold ). I found weird we can found big cities in polar. It don't fit with the lore nor with the reality.
Could be possible to remove the all city settlement in polar but make a new improvement buildable outhere cultural border, like a mix of outpost and ice extractor, sort of fortified ice factory ? this could be built only on ice, and give the ressource benefit, a small bonus defense, and small cultural controle like outpost. So the polar could be only a place were factions fight to gain the control of theses outposts, only for the bonus. And then all the ices tiles still as useless as the deep desert. No more problem of the balance of these city, nor the weird issues of terraforming. (forest in the polar ? even with huge liquid water reservoir, it is not possible due to the lack of... sun. )
Could be possible to remove the all city settlement in polar but make a new improvement buildable outhere cultural border, like a mix of outpost and ice extractor, sort of fortified ice factory ? this could be built only on ice, and give the ressource benefit, a small bonus defense, and small cultural controle like outpost. So the polar could be only a place were factions fight to gain the control of theses outposts, only for the bonus. And then all the ices tiles still as useless as the deep desert. No more problem of the balance of these city, nor the weird issues of terraforming. (forest in the polar ? even with huge liquid water reservoir, it is not possible due to the lack of... sun. )