According to a study published in Geophysical Research Letters, humans have shifted a significant mass of water by pumping it out of the ground and redistributing it elsewhere. This water redistribution has caused the Earth to tilt approximately 80 centimeters (31.5 inches) east between 1993 and 2010. Previous estimates suggested that humans pumped 2,150 gigatons of groundwater, equivalent to over 6 millimeters (0.24 inches) of sea-level rise, during that period. However, validating these estimates has been challenging.

The study focused on the Earth’s rotational pole, which moves during polar motion. The distribution of water on the planet affects the mass distribution and alters the rotational pole. Researchers discovered in 2016 that water could change the Earth’s rotation, but the specific impact of groundwater on rotational changes has not been explored until now. By modeling the observed changes in the drift of the Earth’s rotational pole and the water movement, the researchers found that including 2,150 gigatons of groundwater redistribution in the model matched the observed polar drift. Without it, the model was off by 78.5 centimeters (31 inches) or 4.3 centimeters (1.7 inches) of drift per year.

The study revealed that groundwater redistribution has the most significant impact on the drift of the rotational pole among climate-related causes. The location of the groundwater plays a crucial role in polar drift changes, with water redistribution from midlatitudes having a more significant impact. Western North America and northwestern India experienced the most water redistribution during the study period.

The findings emphasize the need to address groundwater depletion rates, particularly in sensitive regions. Slowing down groundwater depletion could alter the change in polar drift, but this would require sustained conservation efforts over decades. While the rotational pole’s changes due to groundwater pumping do not immediately affect the seasons, they could have long-term climate implications on geological timescales.

The researchers suggest that future research should investigate historical data on polar motion to understand continental water storage variations over the past century. Analyzing polar motion data from the late 19th century onward could provide insights into hydrological regime changes resulting from a warming climate. Understanding these changes in water storage and polar motion can contribute to our knowledge of Earth’s climate system.

References

• Dzombak, R. & American Geophysical Union. (2023, June 15). We’ve pumped so much groundwater that we’ve nudged the Earth’s spin, says new study. Phys.Org; American Geophysical Union. https://phys.org/news/2023-06-weve-groundwater-nudged-earth.html
• Seo, K., Ryu, D., Eom, J., Jeon, T., Kim, J., Youm, K., Chen, J., & Wilson, C. R. (2023). Drift of earth’s pole confirms groundwater depletion as a significant contributor to global sea level rise 1993–2010. Geophysical Research Letters, 50(12), e2023GL103509. https://doi.org/10.1029/2023GL103509