A study finds that groundwater pumping has changed the Earth’s rotation

At the turn of the millennium, the Earth’s rotation began to deviate, and no one could say why.

For decades, scientists have been watching the average position of our planet’s rotational axis, the imaginary rod that orbits it, looping gently south, away from the geographic North Pole and toward Canada. But suddenly, it turned sharply and started heading east.

In time, the researchers came to An amazing realization about what happened. The accelerating melting of polar ice sheets and mountain glaciers has changed the way mass is distributed around the planet enough to affect its rotation.

Now, some of the same scientists have identified another factor with the same effect: massive amounts of water pumped out of the ground for crops and households.

“Wow,” Ki-won Seo, who led the research behind the latest discovery, thought when his calculations showed a strong link between groundwater extraction and the drift of the Earth’s axis. It was a “big surprise,” said Dr. Seo, a geophysicist at Seoul National University.

Water experts have long warned of the consequences of overuse of groundwater, especially as water from aquifers has become an increasingly vital resource in drought-stressed regions like the American West. When water is pumped from the ground but not replenished, the ground can flood, damaging homes and infrastructure and also reducing the amount of subterranean space that can hold water afterward.

Between 1960 and 2000, Groundwater depletion all over the world more than doubled, to about 75 trillion gallons a year, scientists estimate. Since then, satellites that measure variations in Earth’s gravity have revealed the startling extent to which groundwater supplies have declined in certain regions, including India and California’s Central Valley.

“I’m not surprised it would have an impact” on Earth’s rotation, said Matthew Rudel, an Earth scientist at NASA’s Goddard Space Flight Center. Which was Posted this month In Geophysical Research Letters. “And that their observations of polar motion are accurate enough to see this effect.”

The Earth’s axis has not rotated enough to affect the seasons, which are determined by the planet’s tilt. But subtle patterns and variations in the planet’s rotation greatly influence the satellite-based navigation systems that direct aircraft, missiles and mapping applications. This has helped motivate researchers to try to understand why the axis is moving and where it might go next.

You can’t feel it, but our planet’s rotation is nowhere near as smooth as the globe on your desk.

as it moves through space, Earth wobble Like a frisbee thrown in a bad way. This is partly because it bulges at the equator and partly because air masses are constantly circling through the atmosphere and water is sloshing around in the oceans, always pulling the planet this way and that.

And then, there’s this touring hub.

One of the main reasons is that the Earth’s crust and mantle are falling back after being encased by giant sheets of ice for thousands of years, bouncing around like an empty mattress from a sleeper. This has steadily changed the mass balance around the planet.

at recent days, The balance has also changed Through factors closely related to human activity and global climate. They include melting mountain glaciers and ice sheets in Greenland and Antarctica, changes in soil moisture, and our retention of water behind dams.

Another big factor, according to the study by Dr. Seo and colleagues, is groundwater depletion. The study found that, in terms of influencing the Earth’s axis, the pumping of water from underground was the second largest, between 1993 and 2010, only after the modification of the planet’s crust after glaciers.

There are other forces that may be pulling the Earth’s axis in its new direction, but they are not yet fully understood, said Clark Wilson, a geophysicist at the University of Texas at Austin and another author of the study. “It is possible, for example, that there is something in the Earth’s fluid core going on, and that is also contributing,” he said.

Even so, Dr. Wilson said, the latest discovery points to new possibilities for using information about the Earth’s rotation to study climate.

Because scientists have collected high-resolution data about the position of the Earth’s axis for most of the 20th century, they may be able to use it to understand shifts in groundwater use that occurred before the most recent reliable data became available.

It’s a possibility Dr. Seo says he’s already beginning to explore.