According to a new study published in the journal Geophysical Research Letters, humans drained and transferred so much groundwater that the Earth tilted about 80 centimetres (31.5 inches) east between 1993 and 2010.
The rotating pole of the Earth is the point around which the globe revolves. It travels as a result of polar motion, which occurs when the spinning pole of the Earth fluctuates in relation to the crust. The distribution of water on the globe influences the distribution of mass.
“Earth’s rotational pole actually changes a lot,” said Ki-Weon Seo, the study’s lead author and a geophysicist at Seoul National University. “Our research shows that, among climate-related causes, groundwater redistribution has the greatest impact on rotational pole drift.”
The power of water to modify the Earth’s rotation was identified in 2016, but the particular contribution of groundwater to these rotational shifts remained unknown until now. Researchers in the current study modelled the documented changes in the drift of Earth’s rotational pole and water movement — initially with only ice sheets and glaciers in mind, then with various scenarios of groundwater redistribution.
Only after the researchers included 2150 gigatonnes of groundwater redistribution did the model match the observed pole drift. The model was off by 78.5 centimetres (31 inches) without it, or 4.3 centimetres (1.7 inches) each year.
“I’m overjoyed to have discovered the previously unknown cause of rotation pole drift,” Seo remarked. “On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea-level rise.”
“This is a nice contribution and an important documentation for sure,” said Surendra Adhikari, a Jet Propulsion Laboratory research scientist who was not engaged in this work. Adhikari’s research on water redistribution and rotational drift was released in 2016. “They’ve quantified the role of groundwater pumping in polar motion, and it’s pretty significant.”
The location of the groundwater influences how much polar drift is affected; moving water from the midlatitudes has a greater impact on the rotational pole. The greatest water was redistributed throughout the study period in western North America and northern India, both at midlatitudes.
Countries’ efforts to limit groundwater depletion rates, particularly in sensitive areas, might theoretically influence drift, but only if such conservation measures are implemented for decades, according to Seo.
The rotational pole generally varies by a few metres per year, therefore changes caused by groundwater pumping do not threaten shifting seasons. However, on geologic time scales, pole drift can have an effect on climate, according to Adhikari.
