The Earth’s rotational pole has drifted east 31.5 inches, or nearly 80 centimeters, over the course of 17 years as a result of the large amounts of water that humans have pumped out of the ground, says a new study from Geophysical Research Letters.
"Earth's rotational pole actually changes a lot," said Ki-Weon Seo, lead author of the study and a geophysicist at Seoul National University. "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 depletion has been identified as one of the anthropogenic causes of sea level rise. The study authors aimed to understand how groundwater depletion has contributed to global mean sea levels (GMSL), and found observed polar motion (PM) to be a helpful way to track the ways that water has been redistributed around the globe by human activity.
Looking at the period from 1993 to 2010, scientists identified the eastern tilt of 80 centimeters (31.5 inches). The finding has helped to validate previous estimates from climate models that theorized humans pumped 2,150 gigatons of groundwater and produced a resulting 6 millimeters (0.24 inches) of GMSL during the study period (1993 to 2010).
The study’s model began with observed changes in Earth’s rotation pole drift, first taking into account only ice sheets and glaciers, then adding in groundwater redistribution of different amounts. They found that including 2,150 gigatons of groundwater redistribution produced a model that matched the Earth’s observed polar drift.
"I'm very glad to find the unexplained cause of the rotation pole drift," 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."
The researchers also found that when water is redistributed from midlatitudes, it can have a larger impact on the rotational pole, and western North America and northwestern India — two locations at midlatitudes — were the areas from which most water was redistributed during the study period.
Surendra Adhikari, who authored a previous study that discovered water’s ability to affect the Earth’s rotation, said, “They've quantified the role of groundwater pumping on polar motion, and it's pretty significant."
Sources: Geophysical Research Letters, 2023; Phys.org; Geophysical Research Letters, 2010; USGS; Science Advances