Earth’s magnetic poles have been shifted away from the planet’s axis of rotation because of the huge amount of water stored behind man-made dams, a study has found.
The Earth’s crust sits atop a molten rock core, which means it can shift in different directions relative to the magma below it. Any time that mass is redistributed around the planet’s surface, as when ice sheets grow or shrink, causes the outermost rock layer to move around. This means that different areas of the surface end up sitting directly over the axis of rotation. The geographic poles then pass through different spots on the surface than before, a process called true polar wander.
A study published in Geophysical Research Letters finds that the construction of nearly 7,000 dams from 1835 to 2011 shifted the poles about a metre in total and caused a 21mm drop in global sea levels. Together, these dams hold enough water to fill the Grand Canyon twice over.
While the polar shift is relatively small, scientists say it could...