The only reason you can build a city in a desert is the abundance of cheap energy and the ability to build what it needs elsewhere. These two conditions are not met in an hypothetic refuge.
As for soil, the creation of soil in Ireland and the UK took quite a bit of time.
Also, worth considering is that it is virgin territory for exploration for minerals and other goodies.
No shortage of water either.
But even all that aside, it is newly available space. If you can build a city in a desert (Phoenix, Arizona lets say) you can build one on Greenland.