Humans have caused marked tilts in the Earth’s axis by pumping water out of the ground and moving it elsewhere, according to a new study.
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| Groundwater depletion shifting Earth's axis. |
Pronounced shifts in the Earth’s axis of rotation can impact our planet’s climate, noted the study published in Geophysical Research Letters, the journal of the American Geophysical Union, on June 15, 2023.
Groundwater pumping has tilted the planet nearly 80 centimetres east between 1993 and 2010 alone.
The water circulated across the planet determines how mass is distributed. Scientists had predicted that between 1993 and 2010, people pumped 2,150 gigatons of groundwater, or more than 6 millimeters (0.24 inches), of sea level increase. However, it is difficult to validate that estimate.
The planet’s geographic north and south poles are where its axis intersects the surface; however, they are not fixed. The axis and hence the poles fluctuate due to variations in the Earth’s mass distribution.
In the past, the poles’ drift was only caused by natural forces like ocean currents and the convection of heated rock deep beneath the Earth. But the new research pitched the redistribution of groundwater as the primary culprit for the drift.
Earth’s rotational pole actually changes a lot, said Ki-Weon Seo, a geophysicist at Seoul National University who led the study. Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory who was not involved in this study, also agreed with Seo.
Adhikari said the rotational pole normally changes by several metres within about a year, so changes due to groundwater pumping don’t run the risk of shifting seasons. But on geologic time scales, polar drift can have an impact on climate.
“Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole,” Seo added.
Redistributing water from the mid-latitudes significantly influences polar drift; therefore, the location of redistribution determines polar drift. During the study period, most redistribution occurred in western North America and northwestern India — both located at mid-latitudes.
Attempts to slow groundwater depletion rates, especially in those sensitive regions, could theoretically alter the change in drift, but only if such conservation approaches are sustained for decades, Seo said.
Water’s role in altering the Earth’s rotation was discovered in 2016, and until now, the contribution of groundwater to drifts has been unexplored.
In the new study, researchers analysed changes in the drift of Earth’s rotational pole and water movement — first, by accounting for just ice sheets and glaciers and then by adding different groundwater redistribution scenarios.
A 2021 study published in the journal Geophysical Research Letters found that the direction of polar drift moved from southward to eastward in 1995 and that the average drift speed from 1995-2020 was 17 times quicker than from 1981-1995.
In the past 50 years, humans have extracted 18 trillion tonnes of water from aquifers without replacing it, it added.
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Underground Water Pumping side effects on Earth's Axis |
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