>>8454791 /lb
It's possible that a magnetic reversal does not result in a geo-physical flipping of the planet. Best case is the field lines go haywire as the migrate into opposite positions for a period of time, then stabilize. This would make portions of the atmosphere very tenuous, and may result in flash freezing like we see with mammoths that have un-degested flowers in their stomachs (Only possible in a atmospheric vacuum type flash freeze event where the multi-ton animal was solidified, halting digestion from decomposing the stomach contents.)
This is why our ancestors built subterranean caverns all around the world, like Derinkuyu and Giza. It was really the ONLY way to survive.