Human extraction of water has tilted the Earth by 80 centimeters in 17 years

By pulling water out of the ground and moving it elsewhere, humans have displaced a body of water so large that the Earth tilted almost 80 centimeters to the east between 1993 and 2010 alone.

Based on climate models, new research published in Geophysical Research Letters previously estimated that humans pumped 2,150 gigatons of groundwater, equivalent to more than 6 millimeters of sea level rise, between 1993 and 2010.. But validating that estimate is difficult.

One approach lies in the Earth's pole of rotation, which is the point around which the planet revolves.. It moves during a process called polar motion, which is when the position of Earth's pole of rotation varies relative to the crust..

The distribution of water on the planet affects how mass is distributed. Like adding a bit of weight to a spinning top, the Earth spins a bit differently as the water moves.

“Earth's pole of rotation actually changes a lot,” Ki-Weon Seo, a geophysicist at Seoul National University who led the study, said in a statement.

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

The ability of water to change the Earth's rotation was discovered in 2016 and the specific contribution of groundwater to these rotational changes had not been explored until now.. In the new study, the researchers modeled the observed changes in Earth's pole rotation drift and water movement, first considering only ice sheets and glaciers, and then adding different groundwater redistribution scenarios.

The model only matched the observed polar drift once the researchers included 2,150 gigatons of groundwater redistribution.. Without it, the model had a deviation of 78.5 centimeters, or 4.3 centimeters of deviation per year.

“I am very glad to find the unexplained cause of the rotational pole deviation,” Seo said.. “On the other hand, as a resident of Earth and a parent, I am concerned and surprised to see groundwater pumping as another source of sea level rise.”

The location of the groundwater matters by how much polar drift might change; redistributing water from the mid-latitudes has a greater impact on the pole of rotation. During the study period, most of the water was redistributed in western North America and northwestern India, both in mid-latitudes.

Attempts by countries to reduce rates of groundwater depletion, especially in those sensitive regions, could theoretically alter the shift in drift, but only if such conservation approaches are sustained for decades, Seo said.

The pole of rotation normally changes several meters in about a year, so changes due to groundwater pumping do not risk changing the seasons.. But on geologic time scales, polar drift can have an impact on climate, Adhikari said.

The next step in this investigation could be to look into the past.. “Observing changes in the Earth's pole of rotation is useful for understanding variations in water storage on a continental scale,” Seo said. “Polar motion data has been available since the late 19th century. Therefore, we can use these data to understand variations in inland water storage over the last 100 years. Was there any change in the hydrologic regime as a result of global warming? climate? Polar movement could hold the answer.”