Earth is off axis due to excessive pumping of groundwater

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 axis of rotation, 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 paper published in Geophysical Research Letters on June 15.

“The Earth’s rotational 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 largest influence on the change in the Earth’s rotational 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 per hour (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.

From 1993 to 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 raise global sea levels 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 glaciers and ice sheets, 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 will shift and then return to its original position. Seo and his colleagues raised a number of questions about the long-term changes 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 measurements of stationary objects in space using radio telescopes and using these objects as fixed landmarks. In the new study, 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 model-derived groundwater volume change,” 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 centimeters) in less than two decades. A major influence on the Earth’s rotation has long been known as mantle convection—the flow of liquefied rock in the layer between the Earth’s surface and the outer core. The new model shows that groundwater extraction is the second-largest factor after that, Seo said.

“This is an important contribution to the literature,” said Adhikari. “They have quantified the role of groundwater extraction in the movement of the Earth’s axis, 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,” he said. With this information, scientists could look back in time 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 that are severely affected 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 some unintended global consequences.

“We have affected 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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