Earth’s rotational pole has drifted toward 64.16°E at a speed of 4.36 cm per year during 1993-2010 due to groundwater depletion and resulting sea level rise, according to new research.

Seo et al. show that the model estimate of water redistribution from aquifers to the oceans would result in a drift of Earth’s rotational pole, about 78.48 cm toward 64.16°E. Image credit: NOAA.

Melting of polar ice sheets and mountain glaciers has been understood as a main cause of sea level rise associated with contemporary climate warming.

It has been proposed that an important anthropogenic contribution is sea level rise due to groundwater withdrawal resulting from irrigation.

A climate model estimate for the period 1993-2010 gives total groundwater depletion of 2,150 gigatons, equivalent to global sea level rise of 6.24 mm.

“Earth’s rotational pole actually changes a lot,” said Dr. Ki-Weon Seo, a geophysicist at Seoul National University.

“Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”

Water’s ability to change the Earth’s rotation was discovered in 2016, and until now, the specific contribution of groundwater to these rotational changes was unexplored.

In the new study, Dr. Seo and colleagues modeled the observed changes in the drift of Earth’s rotational pole and the movement of water — first, with only ice sheets and glaciers considered, and then adding in different scenarios of groundwater redistribution.

The model only matched the observed polar drift once the researchers included 2,150 gigatons of groundwater redistribution.

Without it, the model was off by 78.5 cm, or 4.3 cm of drift per year.

“I’m very glad to find the unexplained cause of the rotation pole drift,” Dr. Seo said.

“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.”

The location of the groundwater matters for how much it could change polar drift; redistributing water from the midlatitudes has a larger impact on the rotational pole.

During the study period, the most water was redistributed in western North America and northwestern India, both at midlatitudes.

“Countries’ attempts to slow groundwater depletion rates, especially in those sensitive regions, could theoretically alter the change in drift, but only if such conservation approaches are sustained for decades,” Dr. Seo said.

The next step for the team’s research could be looking to the past.

“Observing changes in Earth’s rotational pole is useful for understanding continent-scale water storage variations,” Dr. Seo said.

“Polar motion data are available from as early as the 19th century.”

“So, we can potentially use those data to understand continental water storage variations during the last 100 years.”

“Were there any hydrological regime changes resulting from the warming climate? Polar motion could hold the answer.”

The results were published today in the journal Geophysical Research Letters._

Ki-Weon Seo et al. 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; doi: 10.1029/2023GL103509