May 29, 2024

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Earth Spin Illustration

We have pumped out so much groundwater that the Earth’s rotation has shifted

Groundwater extraction and redistribution by humans has shifted Earth’s rotational pole by nearly a meter in two decades (1993-2010), contributing to sea level rise, a study reveals in Geophysical Research Letters. Most water redistribution has occurred in western North America and northwest India, and efforts to reduce groundwater depletion in such areas could theoretically influence this shift. This phenomenon does not risk changing seasons but may affect the climate on geological timescales.

The mass shift and consequent sea-level rise due to groundwater withdrawal caused the Earth’s rotational pole to wander nearly a meter in two decades.

By pumping water out of the ground and transporting it elsewhere, humans shifted such a large body of water that the Earth tilted nearly 80 cm (31.5 in) east between 1993 and 2010 alone, according to a new study published June 15 in Geophysical Research LettersAGU’s short, high-impact research journal with implications spanning the earth and space sciences.

Based on climate models and scientists previously estimated Humans pumped 2,150 gigatonnes of groundwater, equivalent to more than 6 millimeters (0.24 in) of sea level rise, from 1993 to 2010. But validating this estimate is difficult.

One approach lies at the Earth’s rotational pole, which is the point around which the planet orbits. It moves through a process called polar motion, which is when the position of the Earth’s rotational pole changes relative to the crust. The distribution of water on the planet affects how the mass is distributed. Like adding a little weight to a spinning top, the Earth spins a little differently as it moves water.

“Earth’s rotation pole changes often,” said Ki-wyun Seo, a geophysicist at Seoul National University who led the study. “Our study shows that among climate-related causes, groundwater redistribution actually has the greatest impact on shaft drift.”

Redistribution of groundwater mass with observed polar motion

Here, the researchers compared the observed polar motion (red arrow, “OBS”) to modeling results without (dashed blue arrow) and with (solid blue arrow) groundwater mass redistribution. A model with groundwater mass redistribution is a better match for the observed polar motion, telling researchers about the magnitude and direction of groundwater influence on Earth’s rotation. Credit: Seo et al. (2023), Geophysical Research Letters

It was the ability of water to change the Earth’s rotation Discovered in 2016To date, the specific contribution of groundwater to these circulation changes has not been explored. In the new study, the researchers modeled the observed changes in Earth’s rotational pole drift and water movement—first, taking into account only ice sheets and glaciers, and then adding different scenarios for groundwater redistribution.

The model only matched the polar drift observed once the researchers included 2,150 gigatonnes of groundwater redistribution. Without it, the model was stopped at 78.5 cm (31 in), or 4.3 cm (1.7 in), of drift annually.

“I am very happy to find the unexplained cause of shaft drift,” Seo said. “On the other hand, as a land-dweller and parent, I am concerned and surprised to see that groundwater pumping is another source of sea level rise.”

“This is an amazing contribution and definitely an important documentation,” said Surendra Adhikari, a research scientist at JPL who was not involved in this study. Adhikari published a 2016 paper on water redistribution affecting rotational drift. “They’ve identified the role of groundwater pumping in polar motion, and it’s very important.”

The location of groundwater is important to the extent to which it can alter polar drift; Redistribution of water from mid-latitudes has a greater effect on the shaft. During the study period, most of the water was redistributed in western North America and northwest India, both at midlatitudes.

Seo said states’ attempts to slow groundwater depletion rates, especially in those sensitive areas, could theoretically reverse the change in erosion, but only if such conservation methods persist for decades.

The shaft usually changes by several meters in about a year, so changes caused by groundwater pumping are not at risk of changing seasons. But on geological time scales, polar drift can have an impact on climate, Adhikari said.

The next step for this research may be to look back.

“Observing changes in Earth’s rotational pole is useful for understanding continent-wide differences in water storage,” Seo said. Polar motion data have been available since the late 19th centuryy a century. Therefore, we can use this data to understand the continental differences of water storage over the past 100 years. Have there been any changes in the hydrological regime caused by a warming climate? Polar motion can hold the answer.”

Reference: “Earth’s Pole Drift Confirms Groundwater Depletion as an Important Contributor to Global Sea Level Rise 1993–2010” By Ki-wyun-seo, Dongriol-ryeo, Goyoung-eum, Taeohan-jeon, Jae-seong Kim, Kuhyun-eum, Jianli Chen, Clark R. Wilson, June 15, 2023, Available Here. Geophysical Research Letters.
doi: 10.1029/2023GL103509

Authors:

  • Ki-Weon Seo (corresponding author), Center for Educational Research and Department of Earth Science Education, Seoul National University, Seoul, Republic of Korea
  • Jae-Seung Kim, Kookhyoun Youm, Department of Earth Science Education, Seoul National University, Seoul, Republic of Korea
  • Dongriol Ryo, Department of Infrastructure Engineering, University of Melbourne, Parkville, Australia
  • Jooyoung Eom, Department of Earth Science Education, Kyungbuk National University, Daegu, Republic of Korea
  • Taewhan Jeon, Center for Educational Research, Seoul National University, Seoul, Republic of Korea
  • Jianli Chen, Department of Land Surveying and Geoinformatics, Institute of Earth and Space Research, Hong Kong Polytechnic University, Hong Kong
  • Clark Wilson, Department of Geosciences, and Space Research Center, University of Texas at Austin, Austin, Texas, USA

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