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.
The first factor is glacial rebound or isostatic rebound, what scientists
previously thought was the primary contributor to Earth's wobble. Imagine
Earth as a very large balance ball similar to the one in the photo below.
As you can see, the lady on the balance ball is compressing the ball where
she is in contact with the ball, causing a dent. To compensate for this,
the sides of the ball just outside of the lady's outline bulges outward.
This is an example of when large glaciers cover land masses such as North
America. During the last ice age, about 26.5 thousand years ago, large
expanses of land were covered in heavy glaciers.
This depressed land underneath the glaciers and causes land to bulge
upward around the perimeter of the glaciers. However, as the glaciers
melted, the land, just like the ball would, regain its original shape.
This process is called glacial rebound, as Earth regains its original
shape. The process is quite slow, meaning Earth is still rebounding from
the last ice age. This is what scientists previously thought accounted for
the entire wobble of Earth.
Now, we know that there are two other factors that influence Earth's
wobble. Melting of ice, particularly on Greenland was found by NASA to
account for one-third of Earth's wobble. This surprising finding directly
links human actions with altering Earth's wobble. As humans continue to
artificially warm the planet through releasing greenhouse gases, ice on
land continues to melt at unprecedented rates. NASA estimates that 7,500
gigatons of Greenland's ice have melted into the ocean in the 20th
century. This equals the weight of 20 million Empire State Buildings. The
transfer of weight from Greenland to redistributed across the globe has
caused Earth to wobble more than it would have otherwise.
The last factor, accounting for a third of Earth's wobble is mantle
convection. This is an ongoing process in Earth's interior where molten
rock is heated, rises in the mantle, cools off and falls back closer to
Earth's core. Convection within the mantle is the driving mechanism of
plate tectonics, earthquakes, volcanoes, mountain ranges, and deep sea
In total, NASA found that Earth's spin axis has drifted about 10 meters in
the 20th century alone. As ice continues to melt from continental masses
such as Greenland, we will continue to see an increased wobble as Earth
spins. Thankfully, the wobble is not large enough to impact ecosystems or
our daily life. While it can impact navigation, modern technology can
accurately account for changes in Earth's wobble.
What is surprising is how much humans are changing the fundamental nature
of Earth and how it operates. Continuing to monitor Earth's wobble and its
changes can act as a barometer for how much ice has melted here on Earth
and put human's role on Earth into an astronomical perspective.
I am a geologist passionate about sharing Earth's intricacies with you. I
received my PhD from Duke University where I studied the geology and
climate of the Amazon. I am the founder of Science Trends, a leading
source of science news and analysis on everything from climate change to
cancer research. Let's connect @trevornace Read Less
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