Earth is off axis due to excessive groundwater pumping

Groundwater is an important source of drinking water for humans and livestock, and also provides irrigation during droughts. However, a recent study found that the continuous pumping of groundwater over the past decade has shifted the Earth’s rotation axis, tilting it eastward by about 1.7 inches (4.3 cm) per year.

This annual misalignment can be observed even on the Earth's surface, because of its sea-level-raising effect, the researchers report in a study published in Geophysical Research Letters on June 15.

“The Earth’s rotation axis has actually changed a lot,” said lead author Ki-Weon Seo, a professor in the Department of Earth Science Education at Seoul National University in South Korea, in a press release. “Our study shows that among climate-related causes, groundwater redistribution is the biggest influence on the change of the Earth’s rotation axis.”

Earth's axis of rotation

It is difficult for humans to perceive the rotation of the earth, but in reality the earth always rotates on a North-South axis at a speed of about 1,000 miles/h (equivalent to 1,609 km/h).

Seasonal changes on Earth are closely linked to the planet's rotation axis, and over geologic timescales, a drift in this axis can affect climate on a global scale, said Surendra Adhikari, a research scientist at NASA's Jet Propulsion Laboratory, in a press release.

The Earth's interior is made up of layers of rock and magma surrounding a very hot, dense metallic core. However, beneath the outermost layer of rock lies a vast reservoir of water. Beneath the Earth's surface, the reservoirs are estimated to contain 1,000 times more water than all the rivers and lakes on the Earth's surface combined.

World - Earth is off axis due to excessive groundwater pumping — Over geological time, the Earth's axial drift can affect global climate. Photo: NASA/File.

Between 1993 and 2010, the period analyzed in the study, humans extracted more than 2,150 trillion tons of groundwater from the Earth, mostly from western North America and northwestern India, according to 2010 estimates. For perspective, if that amount of water were dumped into the ocean, it would cause global sea levels to rise by 0.24 inches (6 millimeters).

In 2016, a research team discovered that the Earth's axis tilt from 2003 to 2015 could be related to changes in the mass of ice sheets and glaciers, as well as changes in the amount of water on the Earth's surface.

In fact, any large-scale change on Earth, including changes in atmospheric pressure, could shift the Earth's axis, Seo told CNN via email.

However, Seo explained, the Earth's axis shifting due to changes in atmospheric pressure is a periodic process, or in other words, the Earth's axis of rotation will shift and then return to its original position. Seo and his colleagues raised a number of questions about the long-term change in the Earth's axis, especially the impact of groundwater extraction, a factor that has not been analyzed in previous studies.

Impacts from groundwater exploitation

The Earth's rotational shift can be observed indirectly through radio telescope measurements of stationary objects in space and using them as fixed landmarks. In the new study, the scientists used 2010 groundwater extraction data and fed it into computer models, along with observational data on ice mass loss and sea level rise, along with estimates of the Earth's rotational shift.

The researchers then assessed sea-level change “using the groundwater volume change from the model,” to determine the amount of axial drift caused by groundwater extraction, Seo said.

According to the model, groundwater redistribution has shifted the Earth’s rotation axis eastward by more than 31 inches (78.7 cm) in less than two decades. A long-known major influence on Earth’s rotation is mantle convection currents—flows of liquefied rock in the layer between the Earth’s surface and the outer core. The new model shows groundwater extraction is the second-largest factor after that, Seo said.

“This is an important contribution to the literature,” said Mr. Adhikari. “They have quantified the role of groundwater extraction in the Earth’s axial movement, and this is a remarkable finding.”

Future models could use observations of Earth's rotation to learn more about the past, Seo added. "The data goes back to the 19th century." With this information, scientists can look back and analyze data on changes in the planetary system as the Earth warmed over the past 100 years.

The groundwater industry can be an important resource, especially in areas of the world hit hard by droughts caused by climate change. However, underground water sources are finite, and once depleted, they take a long time to recover.

In addition, groundwater extraction not only depletes a valuable resource, recent findings have shown that the practice has brought with it a number of unintended global consequences.

“We have impacted the earth in many ways, and people need to know about that,” said Mr. Seo.

Nguyen Quang Minh (according to CNN)

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