"Liquid churning in Earth’s core generates most of the magnetic field, which varies over time as the deep flows change." Most of the Earth's mass is our liquid iron core.
The article also points out the the model was last updated in 2015, and they expected they would have to do the next update in 2020.
But they have to do it a bit earlier than projected, because they have a standard for variance to prevent navigational errors (the difference between true North and magnetic North), whose effect is really magnified close to the magnetic poles.
