Groundwater extraction tilted the Earth nearly 80 centimeters in two decades, study finds

According to the NASA Jet Propulsion Laboratory researcher , the pole of rotation normally shifts several meters in a year, so changes due to groundwater pumping do not run the risk of shifting the seasons. 

However, on geologic time scales, polar drift can have an impact on climate.

The extraction of groundwater and its transfer has involved the displacement of such a large mass that the Earth tilted almost 80 centimeters to the east between 1993 and 2010, moving the pole of rotation in that time.

A study published in Geophysical Research Letters indicates that the displacement of masses and the consequent rise in sea level due to the extraction of groundwater has caused the Earth’s pole of rotation (the point around which it revolves) to move almost one meter in two decades.

The arrangement of water on the planet affects the distribution of mass, much like adding a little weight to a spinning top, the Earth spins slightly differently when water is displaced.

“The Earth ‘s pole of rotation changes a lot,” said Ki-Weon Seo, from Seoul National University and director of the research, which has shown that “the redistribution of groundwater is the one that most influences the drift of the pole of rotation”.

The pole of rotation normally changes several meters in a year, so changes due to groundwater pumping do not run the risk of shifting the seasons, according to NASA Jet Propulsion Laboratory researcher Surendra Adhikari, quoted by the American Geophysical Union.

However, on geologic time scales, polar drift can impact climate, said Adhikari, who was not involved in the study but published another study in 2016 on the impact of water redistribution on rotational drift.

The ability of water to change Earth’s rotation was discovered in 2016, but the specific contribution of groundwater to these rotational changes had not been explored until now.

Rising sea levels

The team relied on climate models to estimate that humans pumped 2,150 gigatons of groundwater, equivalent to more than 6 millimeters of sea level rise, from 1993 to 2010. But validating that estimate is difficult.

They then modeled the observed changes in the drift of Earth ‘s pole of rotation and the movement of water, first considering only ice sheets and glaciers and then adding different groundwater redistribution scenarios.

The model only matched the observed polar drift by including 2,150 gigatons of groundwater redistribution . Without it, the model was deviating 78.5 centimeters, or 4.3 centimeters of drift per year.

Seo highlighted his satisfaction at finding “the inexplicable cause of the drift of the rotation pole”, as well as his concern and surprise to see that groundwater pumping is “another source of sea level rise” .

The location of groundwater is important to how much polar drift might change; the redistribution of water from the mid-latitudes has a greater impact on the pole of rotation.

During the period studied, the largest amount of water was distributed in western North America and northwestern India, both in mid-latitudes, adds the American Geophysical Union in a statement.

Attempts by countries to curb rates of groundwater depletion , especially in sensitive regions, could theoretically alter the drift, but only if such conservation approaches are sustained for decades, Seo said.

Observing changes in the Earth’s pole of rotation is useful for understanding variations in water storage on a continental scale.

Since data on polar movement has been available since the end of the 19th century, the researcher considered that it can be used to understand the variations in continental water storage during the last hundred years.

In addition, he pointed out that the polar movement of the Earth could have the answer to whether there were changes in the hydrological regime as a consequence of the warming of the climate.