Supposedly in the 1990s, to help avert the danger of an accidental nuclear exchange by the U.S. and Russia, Russia agreed to target all their ICBMs on the Arctic while the U.S. targeted all their ICBMs on the ocean (Pacific I think)
this of course was largely meaningless as ICBMS still have their original targets in their computers and can switch back to those targets in seconds prior to launch.
But just say some bizarre set of circumstances occurred that led to the two sides firing off all 500 or so of their ICBMs at the Arctic and Pacific respectively.
How many people would be killed?