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Here\u2019s what you\u2019ll learn when you read this story:<\/p>\n
When humans pump groundwater, it has a substantial impact on the tilt of Earth\u2019s rotation.<\/p>\n
Additionally, a study documents just how much of an influence groundwater pumping has on climate change.<\/p>\n
Understanding this relatively recent data may provide a better understanding of how to help stave off sea-level rise.<\/p>\n
Water has mass, and mass has leverage. Move enough groundwater from aquifers onto farms, into cities, and eventually into the ocean, and Earth\u2019s spin changes by a measurable amount.<\/p>\n
The shift is tiny on a planetary scale, but the number still grabs you: between 1993 and 2010, researchers estimated that groundwater depletion nudged Earth\u2019s rotational pole by about 31.5 inches.<\/p>\n
The figure comes from a 2023 study in Geophysical Research Letters<\/a>, which estimated that humans depleted about 2,150 gigatons of groundwater between 1993 and 2010. When researchers added that water movement to their polar-motion model, the model lined up much better with the observed drift of Earth\u2019s rotational pole. The same groundwater loss equaled about 6.24 millimeters\u2014roughly 0.24 inches\u2014of global sea-level rise.<\/p>\n \u201cEarth\u2019s rotational pole actually changes a lot,\u201d Ki-Weon Seo, a geophysicist at Seoul National University and study lead, says in a statement<\/a>. \u201cOur study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.\u201d<\/p>\n Earth\u2019s rotational pole is not fixed in place. It drifts and wobbles as mass shifts around the planet. In 2016, NASA described<\/a> the effect in plain mechanical terms: add weight to one part of a spinning top, and it spins a little differently. Earth is not a tabletop toy, obviously, but the physics rhyme. Shift enough water from land to ocean, and the spin axis responds.<\/p>\n This study in Geophysical Research Letters attempts to add some hard figures to that realization. \u201cI\u2019m very glad to find the unexplained cause of the rotation pole drift,\u201d Seo says. \u201cOn the other hand, as a resident of Earth and a father, I\u2019m concerned and surprised to see that pumping groundwater is another source of sea-level rise.\u201d<\/p>\n The study used data from 1993 through 2010 and estimated that the depletion of about 2,150 gigatons of groundwater helped move Earth\u2019s rotational pole roughly 31.5 inches. Much of that pumping was for irrigation and human use, with water that had been stored underground eventually making its way to the oceans.<\/p>\n In the study, researchers modeled observed changes in Earth\u2019s rotational pole and tested different water-redistribution scenarios. The scenario that best matched the observed drift included 2,150 gigatons of groundwater depletion. While the pole motion helped constrain the groundwater estimate, it wasn\u2019t exactly a before-and-after picture of pumps yanking Earth off balance.<\/p>\n Surendra Adhikari, a research scientist at NASA\u2019s Jet Propulsion Laboratory who was involved in the 2016 study, says the additional research is important. \u201cThey\u2019ve quantified the role of groundwater pumping on polar motion,\u201d he says in a news release, \u201cand it\u2019s pretty significant.\u201d<\/p>\n Moving water out of the midlatitudes has an outsized effect on polar motion, and the 2023 study pointed to heavy groundwater depletion in western North America and northwestern India as especially important to the modeled drift.<\/p>\n A 2026 Journal of Geodesy reappraisal<\/a> using the WaterGAP hydrological model found that terrestrial water storage plays a significant role in polar motion across different timescales. But in that model, the longer-term trend was driven mainly by snow-water-storage changes tied to snowfall patterns and Greenland melt, while groundwater and reservoir storage showed up as smaller but still detectable contributors. The paper also found that its modeled long-term trend still didn\u2019t fully agree with GRACE and satellite-laser-ranging observations.<\/p>\n Scientists are also getting better tools for looking backward. In 2026, researchers introduced TWSTORE<\/a>, a four-decade terrestrial-water-storage reconstruction beginning in 1984, and ML-TWiX<\/a>, a monthly global total-water-storage-anomaly reconstruction covering 1980 to 2012. Both are attempts to push water-storage records deeper into the pre-GRACE era, where the satellite record is thinner and the uncertainties get harder to ignore.<\/p>\n We still need a longer view is badly needed. Polar motion involves groundwater, snow, ice sheets, glaciers, sea-level redistribution, reservoirs, and processes inside Earth itself. While newer research has tightened some pieces of that budget, it hasn\u2019t yet turned the planet\u2019s wobble into a solved equation.<\/p>\n \u201cObserving changes in Earth\u2019s rotational pole is useful,\u201d Seo says, \u201cfor understanding continent-scale water storage variations.\u201d<\/p>\n As for how this affects humans, groundwater depletion can sink land, worsen relative sea-level rise, stress coastal aquifers, and help saltwater push into places that depend on fresh groundwater. A 2026 Nature study of 40 major river deltas<\/a> found that contemporary subsidence now exceeds absolute sea-level rise as the dominant driver of relative sea-level rise for most deltas studied, with groundwater storage showing the strongest relative influence on vertical land motion in 10 of the 40 deltas. Another 2026 global coastal assessment in Nature Water<\/a> found statistically detectable groundwater-level trends in 21 percent of gridded coastal areas, with declines becoming more frequent in the most recent nine years of the study.<\/p>\n