Weird reason Earth’s rotation has shifted

Humans have caused the Earth to shift on its axis by almost a metre through one simple, seemingly innocuous activity.

Humans have caused the Earth to shift on its axis by almost a metre through one simple activity. Picture: NASA

Humans have caused the Earth to shift on its axis by almost a metre through one simple, seemingly innocuous activity.

A new study has found that, by pumping water out of the ground and moving it elsewhere, humans have shifted such a large mass of water that the Earth tilted by nearly 8o centimetres between 1993 and 2010 alone.

The distribution of water on the planet affects how mass is distributed, causing the Earth to spin differently as water moves around.

A model of changes to Earth's rotation. Picture: NASA

Sea level rise, commonly associated with climate change, is one of the most significant ways that water can move around the globe.

But scientists estimated that humans pumped some 2150 gigatons of groundwater — enough to fill 860 million Olympic-size swimming pools — in the seven-year period. The quantity amounted to about six millimetres in sea level rise.

“Earth’s rotational pole actually changes a lot,” said Ki-Weon Seo, a geophysicist at Seoul National University who led the study.

“Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”

Groundwater pumping at a winery in California. Picture: Universal Images Group via Getty Images

Water’s ability to change the Earth’s rotation was discovered in 2016 but, until now, the specific contribution of groundwater remained unexplored.

In the new study, which was published in the American Geophysical Union’s Geophysical Research Letters, researchers modelled the observed changes in the drift of the Earth’s rotational pole and the movement of water.

First, they included only ice sheets and glaciers before accounting for different scenarios of groundwater distribution.

They found that the model matched the observed polar drift only when it included 2150 gigatons of groundwater distribution. Without that groundwater, the model was off by 78.5 centimetres.

“I’m very glad to find the unexplained cause of the rotation pole drift,” Associate Professor Seo said.

“On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea-level rise.”

Earth’s rotational pole normally changes by several metres each year, so changes due to groundwater pumping don’t risk monumental impacts like the shifting of seasons. On geological time scales over millions of years, though, polar drift can have an impact on climate.