Europe's Swarm constellation of satellites have documented bigger-than-expected changes
that have been occurring in the Earth's magnetic field. Earlier this year SpaceWeather.com reported that the data show clearly that "the field has weakened by about 3.5% at high latitudes over North America, while it has strengthened about 2% over Asia. The region where the field is at its weakest -- the South Atlantic Anomaly -- has moved steadily westward and weakened further by about 2%. These changes have occurred over the relatively brief period between 1999 and mid-2016
Science writer Robert Zimmerman reports:
It was already known that the field has weakened globally by about 10% since the 19th century. These changes appear to be part of that generally weakening. Some scientists have proposed that this is the beginning of an overall flip of the magnetic field's polarity, something that happens on average about every 300,000 years and last occurred 780,000 years ago. At the moment, however, we have no idea if this theory is correct.