Pumping groundwater for farming and drinking has nudged Earth’s rotational pole by 31.5 inches (80 cm) from 1993 to 2010, according to a study reported in Geophysical Research Letters. This shift reflects the movement of about 2,150 gigatons of water from land areas into the oceans, contributing roughly 0.24 inches (6 mm) to global sea-level rise.
Lead author Ki-Weon Seo, a geophysicist at Seoul National University, said groundwater loss now surpasses all other climate-linked drivers of polar drift. “The rotational pole of Earth actually varies quite a bit,” Seo noted. “Our findings show that, among climate-related factors, groundwater redistribution has the strongest influence on the pole’s movement.”
The underlying idea is straightforward: shifting mass on a rotating object alters how it spins. As the authors put it, “Similar to placing a small weight on a spinning top, Earth’s rotation changes slightly as water is redistributed.”
Earlier NASA work in 2016 showed that water storage changes can affect Earth’s rotation, but the new research gives precise estimates. Seo and colleagues tested several simulations of observed polar motion, and only the scenario that included the 2,150-gigaton groundwater shift aligned with satellite and astronomical observations.
Surendra Adhikari, a scientist at NASA’s Jet Propulsion Laboratory involved in the 2016 study, emphasized the relevance of the new results. “They’ve placed a number on groundwater pumping’s effect on polar motion, and it’s quite substantial,” he said in a NASA release.
Geography plays a role too. Water removed from mid-latitude regions has the strongest impact on the spin axis, which means heavy extraction in western North America and north-western India has contributed significantly to the observed drift.
Because the effect is now visible over just a few recent decades, researchers hope to look back at historical records of Earth’s orientation to track older episodes of groundwater depletion.
“Monitoring shifts in the rotational pole helps us understand how water storage changes across continents,” Seo said. Such insights may also guide water-management decisions aimed at slowing sea-level rise and mitigating climate impacts — assuming those measures are acted on soon enough.