Humans are causing the Earth to wobble as it spins on its axis, found a recent in-depth study conducted by NASA.

Based on measurements from the 20th Century, scientists were able to discover that the planet's spin axis has drifted to about 4 inches or 10 centimeters per year. Over the past century, the Earth has drifted more than 10 meters or 11 yards.

The study was published in the journal Earth and Planetary Science Letters.

The Earth Moving In Odd Ways

Part of the reason why the planet wobbles as it spins on its axis is the uneven distribution of weight on the surface. Earth is not a perfect sphere; it is actually an oblate spheroid. When it rotates on its spin axis, it drifts and it wobbles. The process is called "polar motion."

However, researchers from NASA believe that there are three factors that are primarily responsible for the wobble: glacial rebound, mantle convection, and melting of ice.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis," explained Surendra Adhikari of NASA's Jet Propulsion Laboratory. "But recently, many researchers have speculated that other processes could have potentially large effects on it as well."

The redistribution of mass on Earth in the past century, particularly the melting of ice sheets into the ocean in Greenland, has affected the planet's natural rotation. While ice melts in different locations around the world due to rising temperatures caused by climate change, Greenland is believed to be a primary suspect because of its location.

Throughout the 20th century, 7,500 gigatons of Greenland's ice has melted into the ocean.

The two other causes, however, naturally occurs. During the last ice age about 26 thousand years ago, vast expanse of land was covered with heavy glacier, causing the depressed land underneath to bulge upward and around the perimeter of the glacier.

However, when the glaciers melted, the land slowly rebounded or regained its original position. This is what scientists call glacial rebound and, because it is a very slow process, the land is still trying to rebound from the last ice age.

Meanwhile, mantle convection is the movement of the tectonic plates under the surface of the Earth. This is caused by the heat coming from the planet's core.

What Can Be Done

While the human race cannot do anything to control the glacial rebound and mantle convection, the redistribution of mass caused by the melting of ice into the ocean can still be remedied. If Greenland continues to lose ice because of climate change, polar motion will likely accelerate, too.

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