It affects rectification of AC to DC in some way.
the process takes thousands of years to complete, but along the way there are periods of stregnthening and weakening, and even multiple poles, which can expose various parts of the Earth, and aircraft in flight, to increased radiation levels.
Rapidly changing electromagntic fields caused by solar flares could potentially cause over voltage conditions in equipment but I would have thought that the changes in the earths magnetic field we are talking about here would be far too slow to have the same affect. Our AC system operates at 50Hz so thats 50 cycles a second, a change in polarity of the earths magnetic field would need to be on a similar time scale or faster. Solar flares cause waves of electromagnetic radiation which travel at the speed of light, when they move through electrical equipment at that speed they could produce a very fast changes in electromagnetic fields which inturn could induce large overvoltage transients into said equipment. Same goes for an electromagnetic pulse from a nuclear bomb or something.
I'll be honest though I know very little about the changing polarity of the poles so maybe that produces waves of electromagnetism too???