ionizing radiation will no doubt be quite above nominal for a significant time because the magnetic flux fields actually protect us from solar and other radiation.
WHY do the poles flip? There are several hypotheses about it and my favorite is to think of our planet like a big beach bal full of oil. If the beach ball is spun around it begins to wobble and this wobbling cause the oil to flop around on the inside and slosh around until the sloshing is no longer evenly spinning about. The earths magnetic field is the result of this sloshing about of the liquid core and semi liquid mantle. The mass of material is shifted about and takes several hundred thousand years to cause the dipole to migrate about. The migration and decrease in field strength occur at about the same time and over a period of several thousand years, the whole dipole shuts down and flips until the present North Seeking pole becomes a SOuth seeking pole. and sometimes , (like what we see now) several N and S poles just show up in the middle of ocean plate segments.
Everyone who works in this area agrees that we are now in the initial stages of a polar reversal. Will it be a biggy like the last one , which we call the BRunhes reversal. OR will it be like the several mini reversals just before the Brunhes(Jaramillo, Cobb Moiuntain, Olduvai) These last 3 were short lasting <200 K years and were regionally felt rather than planet wide.
We were busy evolving diuing the Brunhes and we seemed to have made it . Now, having said that, several of past magnnetic reversals occur at the same time as we have Era breaks(climate changes, mini mass extinctions etc)
Maybe the "end of the world" in Oct 2011 has some science behind it , who the hell knows?