Human-driven climate change is intensifying Earth’s natural wobble, according to a new study published in Earth and Planetary Science Letters.
A team led by Surendra Adhikari of NASA’s Jet Propulsion Laboratory (JPL) suggests that humans are exacerbating polar motion—the wobble of Earth along its North-South axis—with activities such as fossil fuel consumption, which releases greenhouse gases that warm the planet and melt glaciers.
As Earth rotates, it tilts back and forth along its polar axis like a spinning top that has been nudged slightly. Polar motion is a result of Earth being lumpy and oblong in places, as opposed to being a perfect sphere. This phenomenon is distinct from Earth’s axial precession, another type of rotational wobble caused by the gravity of the Sun and the Moon, that occurs on a cycle of about 26,000 years.
Changes in surface geometry and mantle dynamics can influence the planet’s wobble. These changes have occurred throughout Earth’s history, and are not inherently dangerous to life, but anticipating such shifts is important for the performance of satellites, such as the Global Positioning System (GPS) constellation.
The effects of Greenland’s ice loss over the past century has had a particularly pronounced impact, according to the research, because this Arctic nation is located at an ideal position to throw Earth’s spin off-kilter.
"There is a geometrical effect that if you have a mass that is 45 degrees from the North Pole—which Greenland is—or from the South Pole (like Patagonian glaciers), it will have a bigger impact on shifting Earth's spin axis than a mass that is right near the Pole," said co-author Erik Ivins, a JPL scientist, in a statement.
Greenland lost 7,500 gigatons of ice mass over the course of the 20th century, in large part due to human-driven climate change. As visualized in this interactive web tool from the team, Earth’s wobble has shifted about 10 meters over the past 100 years, and humans are partly to blame.
That said, we are not the only driving force behind polar motion. As the last Ice Age came to a close some 12,000 years ago, glacial cover receded to the poles. Swaths of continental land, long compressed under the weight of heavy icefields, then expanded in an effect called “glacial rebound,” which has also influenced Earth’s wobble.
Another natural factor called mantle convection, a process of cycling hot material through Earth’s molten mantle, also plays a role in Earth’s polar motion.
The JPL team estimates that anthropogenic climate change, glacial rebound, and mantle convection have had roughly equal impacts on Earth’s wobble over the past century.
Fortunately, these wobble shifts are not expected to have any dire consequences for life on Earth. But they are a reminder that our behavior is altering our world on the largest scales.
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