According to a recent study published in Geophysical Research Letters, the extraction and redistribution of groundwater by humans have caused a significant shift in the Earth’s rotational pole, leading to rising sea levels. The study, which examined the period between 1993 and 2010, highlighted that the most substantial water redistribution occurred in western North America and northwestern India. The findings suggest that efforts to mitigate groundwater depletion in these regions could potentially influence this rotational shift. While the phenomenon is not expected to disrupt seasons, it may have long-term climate implications.
The movement of a vast amount of water resulting from groundwater withdrawal has caused the Earth to tilt approximately 80 centimeters (31.5 inches) eastward within just two decades (1993-2010). This groundbreaking research, published on June 15 in Geophysical Research Letters, a renowned journal for concise and impactful studies in Earth and space sciences, reveals the profound impact of human activities on the Earth’s rotation and its consequences for the planet.
Previously, scientists estimated that humans extracted 2,150 gigatons of groundwater between 1993 and 2010, equivalent to a sea level rise of over 6 millimeters (0.24 inches). However, confirming this estimate has been challenging.
One approach to validate the estimate involves studying the Earth’s rotational pole, the point around which the planet rotates. The pole’s movement, known as polar motion, occurs when its position varies relative to the Earth’s crust. The distribution of water across the planet influences the distribution of mass. Similar to adding a minute amount of weight to a spinning top, the Earth’s rotation is subtly altered as water is redistributed.
“This study demonstrates that the Earth’s rotational pole undergoes significant changes, with groundwater redistribution having the largest impact among climate-related factors,” said Ki-Weon Seo, a geophysicist from Seoul National University who led the study.
The researchers compared the observed polar motion with modeling results that considered various scenarios of groundwater redistribution. Only when they incorporated the redistribution of 2,150 gigatons of groundwater did the model accurately match the observed polar drift. Without this factor, the model deviated by 78.5 centimeters (31 inches), corresponding to an annual drift of 4.3 centimeters (1.7 inches).
The discovery that water can influence the Earth’s rotation was made in 2016, but until now, the specific contribution of groundwater to these rotational changes remained unexplored. In this new study, researchers used models to simulate changes in the Earth’s rotational pole drift by considering ice sheets, glaciers, and various scenarios of groundwater redistribution.
“This research is a valuable contribution and an essential documentation,” said Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory who was not involved in the study. Adhikari previously published a 2016 paper on the impact of water redistribution on rotational drift. “They have quantified the role of groundwater pumping in polar motion, and it is quite significant.”
The location from which groundwater is redistributed affects the extent of polar drift. Redistributing water from mid-latitudes has a more pronounced effect on the rotational pole. During the study period, the greatest water redistribution occurred in western North America and northwestern India, both situated at mid-latitudes.
Seo noted that attempts by countries to reduce groundwater depletion rates, especially in these vulnerable regions, could potentially influence the rotational drift. However, such conservation efforts would need to be sustained for decades to have a noticeable impact.
It is important to note that groundwater pumping-induced shifts do not pose a risk of altering seasons, as the rotational pole normally undergoes several meters of change within a year. Nevertheless, on geological time scales, polar drift can have climate-related implications, according to Adhikari.
The next phase of this research could involve investigating historical data.
“Monitoring changes in the Earth’s rotational pole can provide valuable insights into variations in continental-scale water storage,” explained Seo. “Polar motion data has been available since the late 19th century, offering the potential to understand changes in continental water storage over the past century. Were there any hydrological regime changes resulting from climate warming? Polar motion might hold the answers.”
Reference: “Drift of Earth’s Pole Confirms Groundwater Depletion as a Significant Contributor to Global Sea Level Rise 1993–2010” by Ki-Weon Seo, Dongryeol Ryu, Jooyoung Eom, Taewhan Jeon, Jae-Seung Kim, Kookhyoun Youm, Jianli Chen, Clark R. Wilson, 15 June 2023, Geophysical Research Letters.
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
Dongryeol Ryu, Department of Infrastructure Engineering, The University of Melbourne, Parkville, Australia
Jooyoung Eom, Department of Earth Science Education, Kyungpook 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 Geo-informatics, and Research Institute for Land and Space, Hong Kong Polytechnic University, Hong Kong
Clark Wilson, Department of Geological Sciences, and Center for Space Research, University of Texas at Austin, Austin, TX, USA