There was a large glacier stretching across Southern Sweden during this period. It is likely the local weather was a bit cool and probably inhibited settlement of Scandinavia in general. Anyway, Thor Hyerdahl demonstrated that the Asyr didn't arrive in Norway until AFTER AD 1.
Which proves nothing, for other Nordic tribes had been there for millennia before that. See Barry Fell, Bronze Age America.
The coasts of Norway were and are warmed by the Gulf Stream, and I disagree that a glacier existed in SCen Sweden as late as the time of Christ.
It WAS very wet and boggy, though. The milder, rockier, coasts of Norway and such sheltered areas as the Oslo fjord held many Nordic people through the difficult "chilly" era some 700 bc-300ad +/-