The spin of the planet tilted 31.5 inches to the east between 1993 and 2010 due to humans pumping groundwater, according to a new study.

The big picture: Earth’s rotational axis drifts naturally but its direction shifted east in the 1990s. Previous research attributed that drift to large amounts of water being moved by glacial melt, groundwater removal and other activities that contribute to rises in sea level.

When a large mass of water is moved, the planet's center of gravity also moves.

What's new: Researchers at Seoul National University determined "the redistribution of groundwater actually has the largest impact on the drift of the rotational pole," geophysicist Ki-Weon Seo said in a press release.

The researchers modeled how the drift in Earth's rotational axis changed and how water moved from the melting of ice sheets and glaciers as well as the redistribution of groundwater.
They found the distribution of groundwater had to be included in the model for it to match observations of the shift.
"Earth's pole has drifted toward 64.16°E at a speed of 4.36 cm/yr during 1993–2010 due to groundwater depletion and resulting sea level rise," the authors report.

The impact: Changes in the rotational pole due to groundwater pumping aren't expected to shift the planet's seasons, Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory who was not involved in the study, said in the release.

It normally drifts several meters in a year and the groundwater contribution is on the order of centimeters.
Over time, though, the drift could affect the planet's climate, Adhikari says.