Over the course of about two decades, humans pumped enough water out of the ground that we shifted Earth’s poles by almost a metre. This is equivalent to the polar drift caused by melting Greenland ice over the same period.
“Most people would go about their lives and wouldn’t be aware of [Earth’s] wobbles or the drift,” says Clark Wilson at the University of Texas at Austin. He and his colleagues modelled how changes in the distribution of water around the planet have affected the drifting of the poles.
Some of that polar wander is down to natural causes. Because Earth isn’t a perfect sphere, it wobbles like a top several metres each year. The poles also drift due to changes in the distribution of mass around the planet, such as the movement of water due to the seasons.
“There are a number of things contributing to polar drift, and they all add up,” Wilson says. Filling reservoirs and pumping groundwater, as well as climate change melting glaciers and the resulting sea level rise all contribute, though it wasn’t clear what was the influence of each specific change.
Wilson and his colleagues modelled the drift using estimates of the amount of groundwater pumped between 1993 and 2010, which totalled around 2100 gigatonnes, and the associated rise in sea level, which they estimated at 0.3 millimetres per year.
The polar drift attributed to these changes from groundwater pumping amounted to about 80 centimetres. Wilson says this is especially due to large aquifers located at mid-latitudes, which have the greatest effect on polar drift. The only thing that affected the drift more than changes in groundwater was the rebound of landmasses after the lost weight of melted glaciers from the previous ice age.
This doesn’t itself have particular consequences in terms of changes in the length of day or of the seasons, says Wilson. Although he says that knowing the precise location of the axis is essential for any GPS technology to work.
But the finding illustrates how much water people have pumped, says Manoochehr Shirzaei at Virginia Tech. “The precise number doesn’t matter really,” he says. “What matters is that the volume is so gigantic that it can impact the polar drift of the Earth.”
Groundwater pumping has accelerated in the 21st century, in part due to drought conditions driven by climate change, as well more crops growing in dry places, says Shirzaei.