How does magnetic variation change over time?

Magnetic variation, also known as magnetic declination, changes over time primarily due to changes in the Earth's magnetic field. The Earth's magnetic field is dynamic and does not remain constant; it is influenced by various geological processes occurring deep within the Earth, as well as the movement of tectonic plates. This results in gradual shifts in the magnetic poles and alterations in the strength and direction of the magnetic field.

As these changes occur, magnetic variation at specific locations also shifts, which is why aviators must regularly consult updated aeronautical charts and resources for the most current values of magnetic declination. Understanding these changes is crucial for accurate navigation, as pilots use magnetic heading in conjunction with their instruments, and even small discrepancies can lead to significant navigational errors over time.

While other factors like instrument calibration and solar activity can affect navigation, they do not directly cause the long-term changes in magnetic variation. Thus, the key factor influencing how magnetic variation changes over time is the ongoing evolution and shifts in the Earth's magnetic field itself.