If somehow the glaciers and icecaps started growing again instead of shrinking like they are now, it might be a tough call. A lot of currently inhabited land would be lost if they went to the same positions as they have been previously, but keep in mind that's a lot of water being locked up which would lower sea level, so you'll get things back like the land bridge between Alaska and Russia.
IMO, northerly places such as Canada and Europe would begin to be covered in ice, meaning all those people who live there now would have to move. This would likely cause problems for places that aren't being covered in ice, and tensions would arise from that. Food sources would be lost so others would have to be found and such. I see a lot of bad from it.