At the end of the movie, Dennis Quaid and his partner are trekking to New York to find his son (Jake Gyllenhaal) and his friends. When they get there, they check the GPS tracking system and find that they are right over the library where Dennis' son should be. They are concerned because the land is now snow and ice and they fear that the kids have frozen to death. They don't know that the kids have been surviving by keeping warm next to a fire they have built in an upstairs room of the library. If Dennis Quaid and his partner were standing above (or anywhere near) the library, wouldn't they have been able to see the smoke from the fireplace?