An in-depth study conducted by NASA found that humans are responsible for the increasing wobble detected as Earth spins on its axis.

When you think of Earth you may think of an exact sphere, but Earth is actually an oblate spheroid, pockmarked with mountains and deep ocean trenches. These all combine to unevenly distribute weight across Earth’s surface. This uneven distribution of weight on Earth’s surface is one reason why Earth wobbles on its axis as it spins.

Recent research by NASA found that the wobble of Earth as it spins is broken up into three primary factors: glacial rebound, melting of ice, and mantle convection. Previously, scientists believed glacial rebound to be the primary factor in causing Earth to wobble. However, NASA believes three factors are equally responsible for about a third of Earth’s wobble. Let’s cover the three factors and what they mean. But first, you may find it interesting to visit NASA’s interactive polar motion simulation.