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20 June 2023
By
Sascha
Pare
Human impact on Earth's tilt leaves researchers
'surprised and concerned'
![](images/images_06_20_2023/pic3.png)
Water pumped from aquifers between 1993 and 2010 caused
sea levels to rise and the planet's axis to tilt eastward.© Space
Frontiers/
Archive Photos/Hulton Archive/Getty Images
Humans pumped and displaced so much groundwater in just two decades
that we shifted the tilt of Earth's axis, new research suggests.
Earth's rotational pole — the point around which the planet
rotates — shifts with changes in the distribution of mass across the
globe, wobbling and wandering in a process called polar motion. While
scientists knew that changes in water distribution resulting from
climate change could contribute to polar motion, the impact of
groundwater depletion was unknown.
Now, researchers estimate that by pumping 2,150 gigatons of
water — almost enough water to fill Lake Victoria in Africa, and
equivalent to the weight of 5.5 million Empire State Buildings — from
underground layers of water-saturated rock known as aquifers, humans
caused a "pretty significant" eastward shift of 31 inches (80
centimeters) in Earth's rotational pole between 1993 and 2010.
That's because groundwater used for irrigation and other human
activities eventually ends up in the ocean, which redistributes mass
from where the water was taken to other parts of the globe.
Related: Earth tipped on its side (and back again) in 'cosmic
yo-yo' 84 million years ago
"Earth's rotational pole actually changes a lot," research
leader Ki-Weon Seo, a geophysicist at Seoul National University in
South Korea, said in a statement. "Our study shows that among
climate-related causes, the redistribution of groundwater actually has
the largest impact on the drift of the rotational pole."
What's more, the extracted groundwater that ended up in the
oceans may have boosted global sea level rise by around 0.25 inch
(6.24 millimeters). "Groundwater depletion is a significant
contributor to sea level rise," the researchers wrote in the study,
published June 15 in the journal Geophysical Research Letters.
Globally, roughly 70% of the water pumped from the ground is
used for irrigation, but only half of that trickles back down to
replenish aquifers and other freshwater sources. The other half
evaporates and ends up in the ocean through rainfall.
To determine how much groundwater depletion and resulting sea
level rise contributed to polar drift, geophysicists built a model of
polar motion that accounted for shifts in water mass associated with
thinning ice sheets, melting glaciers and water storage in reservoirs.
When they excluded groundwater redistribution from the model,
the results did not match observed eastward polar drift and, instead,
predicted a much more westward tilt.
When they added the 2,150 gigatons of water from aquifers into
the model, the results matched up with recorded observations of
Earth's eastward drift.
"This is a nice contribution and an important documentation for
sure," said Surendra Adhikari, a research scientist at NASA's Jet
Propulsion Laboratory and co-author of a 2016 study in the journal
Science Advances that looked into the impact of water redistribution
on polar drift.
"They've quantified the role of groundwater pumping on polar
motion, and it's pretty significant," Adhikari said in the statement.
Other "non-negligible" changes in water and mass distribution
may have played a role in polar motion between 1993 and 2010 —
including shifts in natural lake levels, mantle convection and
earthquakes. However, these are difficult to quantify, and no global
database currently exists, the authors wrote in the study.
While polar shifts recorded in the last few decades are
unlikely to affect the length of days or seasons, the finding
illustrates just how much water humans have pumped from the ground.
"I’m concerned and surprised," Seo said in the statement.
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