‘Surprised and concerned’: Scientists find groundwater extracted by humans has shifted tilt of Earth’s axis

A new study has left scientists surprised and concerned after it was found that humans have pumped out so much groundwater in the past two decades that it has shifted the tilt of the Earth’s axis. According to the findings of the research published in Geophysical Research Letters, a journal by the American Geophysical Union, the Earth has tilted as much as 80 centimetres (31.5 inches) between 1993 and 2010, which has been attributed to humans pumping out groundwater and moving it elsewhere.

How much groundwater has been extracted?

The study, based on climate models, has said that an estimated 2,150 gigatonnes of water have been pumped out between 1993 and 2010 which is enough water to fill Lake Victoria in Africa and would weigh as much as 5.5 million Empire State Buildings.

Additionally, the extracted water which ended up in the oceans also contributed to six millimetres of sea level rise. However, the researchers have noted that validating this estimate is difficult.

Earth’s axis and water

The phenomenon of water’s influence on Earth’s rotation was discovered in 2016 but until recent research, there was nothing known about the contribution of groundwater to these changes on the planet’s axis.

The researchers for this study first modelled the observed changes in the drift of Earth’s rotational pole and the movement of water with only ice sheets and glaciers and later with different scenarios of groundwater redistribution.

It was found that the model only matched the observed polar drift once the researchers included 2150 gigatones of groundwater redistribution without which it was off by around 78.5 centimetres (31 inches), or 4.3 centimetres (1.7 inches) of drift per year.

The study also noted the impact of the location of the groundwater on the change in the polar drift as most of the waterwas redistributed in western North America and northwestern India during the time period studied. Since both regions are at midlatitudes, researchers observed that redistributing water from the midlatitudes has a larger impact on Earth’s rotational pole.

“Countries’ 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,” said Ki-Weon Seo, a geophysicist at Seoul National University in South Korea, who led the study, in a statement.

He also spoke about how this study finds “that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”

‘Surprised and concerned’ about the findings

Seo also said that he is “very glad” about finding the “unexplained cause of the rotation pole drift.” However, “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”.

Speaking about the step forward, the lead author said that since polar motion data is available dates back to the late 19th century, it could potentially be used to understand continental water storage variations during the last century.

“Were there any hydrological regime changes resulting from the warming climate? Polar motion could hold the answer,” said Seo. Surendra Adhikari, a research scientist at NASA’s Jet Propulsion Laboratory, who was not involved in the study, said that the study was about to quantify “ the role of groundwater pumping on polar motion, and it’s pretty significant.”

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