What primarily dictates the minor, measurable adjustments occurring to the spin axis in the modern era?

Answer

Movement of mass across the planet's surface and interior

Modern adjustments cause the axis to drift slightly because the Earth is not perfectly rigid, and movement of mass changes the moment of inertia, requiring the axis of rotation to adjust.

What primarily dictates the minor, measurable adjustments occurring to the spin axis in the modern era?

#Videos

The Earths Tilt - YouTube

Earthplanetrotationtiltaxis