There is some evidence of this. Its called the South Atlantic Anomaly.There is evidence that the geomagnetic field is weakening here.The SAA is produced by a "dip" in the Earth's magnetic field at that location, caused by the fact that the center of Earth's magnetic field is offset from its geographic center by 280 miles.
The Earth will switch it’s poles completely, once the Sun does the same.
It happens all the time (geologic time).
The main effect is that compasses will have to be reversed.