Humans are responsible for some of the wobble in Earth’s spin.
Since 1899, the Earth’s axis of spin has shifted about 34 feet (10.5 meters). Now, research quantifies the reasons why and finds that a third is due to melting ice and rising sea levels, particularly in Greenland — placing the blame on the doorstep of anthropogenic climate change.
Another third of the wobble is due to land masses expanding upward as the glaciers retreat and lighten their load. The final portion is the fault of the slow churn of the mantle, the viscous middle layer of the planet.
“We have provided evidence for more than one single process that is the key driver” for altering the Earth’s axis, said Surendra Adhikari, an Earth system scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, and a lead researcher on the new study. [Why Does the Earth Rotate?]
Scientists have long known that the distribution of mass around the Earth determines its spin, much like how the shape and weight distribution of a spinning top determines how it moves. Also, Earth’s spin isn’t perfectly even, as scientists know thanks to slight wiggles in the movements of the stars across the night sky that have been recorded for thousands of years, said Erik Ivins, a study co-author and a senior research scientist at JPL. Since the 1990s, space-based measurements have also confirmed that the Earth’s axis of rotation drifts by a few centimeters a year, generally toward Hudson Bay in northeastern Canada.