According to a new study, published June 15 in the journal Geophysical Research Letters, moving all that water has shifted the Earth to tilt 31.5 inches to the east.
Many people may think that the earth is round, but it is not; it is an oblate spheroid, with long ridges and deep ocean trenches that distribute the mass unevenly and make the Earth look like a potato. The whole thing is also rotating like a surface, and if you move enough mass from one place to another, the earth will vibrate as it spins.
“I liken it to a water softball,” said James Famiglietti, a hydrologist at Arizona State University who was not involved in the study. “When a softball or baseball gets wet, it soaks up water, and when you throw it, it vibrates funny.” This is what is happening here.”
The axis of rotation, or the imaginary line along which the planet rotates, is known as the Earth’s rotational pole. The tree is tilted about 23.5 degrees in relation to our orbit around the sun, which is why we have seasons. The exact location of the pole changes dramatically as the Earth rotates, a phenomenon called polar motion, said Ki-Weon Seo, a geophysicist at Seoul National University and lead author of the study.
“It changes every minute – about 10 meters a year,” Seo said. “The wind, [ocean] tides, barometric pressure or ice – any kind of change can cause polar movement.”
But recently, scientists have realized how much human activity can also cause polar movement.
A 2016 study showed that climate-driven changes in water distribution could cause global water prices to fluctuate. But the findings in this study did not fully explain the polar trend.
With 17 years of experience, Seo and his colleagues used a computer system to model the effects of the Earth’s tilt. To Seo’s surprise, the polar motions were exactly the same as what he saw when pumping groundwater.
“We have many dams, and there are many reservoirs on land, so at first I thought that should be very important,” said Seo, “but actually it is not.” When I included the state of the groundwater, I was able to explain everything [of the] things to watch.”
Changes in the Earth’s tilt are too small to affect the weather or climate, Seo said. However, a team of scientists found that polar drift can be used to estimate the effects of pumping seabed water.
When water is absorbed from the ground to irrigate crops and meet the world’s freshwater demands, it eventually flows through rivers and other channels to the world’s oceans. From 1993 to 2010, the researchers found, groundwater pumping changed enough mass to contribute to 0.24 inches of global sea level rise.
“Groundwater pumping is one of the few management decisions that can be made about how to reduce sea level rise,” Famiglietti said. “We have a lot of interest in the world, and we really need to take good care of the world.”
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