Earth’s axis shift. The reason is about us

At the turn of the millennium, Earth’s rotation began to become lopsided, and no one knew why.

For decades, scientists have watched the average position of our planet’s rotational axis, the imaginary rod that orbits it, drift ingeniously south, away from the geographic North Pole and toward Canada. However, all of a sudden, it made a sharp turn and started heading east.

Over time, the researchers got to A surprising conclusion about what happened. The accelerated melting of the polar ice caps and mountain glaciers has changed the distribution of mass around the planet so much that it has affected its rotation.

Now, some of those scientists have identified another factor that had the same effect: massive amounts of water pumped from the ground for crops and homes.

“How incredible,” thought Ki-won Seo, who led the research behind this latest discovery, when his calculations showed a strong link between groundwater extraction and the movement of the Earth’s axis. It was a “big surprise,” said 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-affected regions, such as the American West. When water is pumped from the ground, but not replenished, the ground can subside, damaging homes and infrastructure in the process, as well as reducing the amount of underground space that can then hold water.

Between 1960 and 2000, more than double the number groundwater around the worldIt reaches about 284 billion liters annually, according to scientists’ estimates. Since then, satellites measuring variations in Earth’s gravity have revealed the staggering level of depletion of groundwater supplies in certain areas, such as India and California’s Central Valley.

“I’m not surprised by the effect” on Earth’s rotation, said Matthew Rudel, a geologist at NASA’s Goddard Space Flight Center (GSFC). Still, “it’s impressive that they were able to decipher it from the data,” Rudel said, referring to the authors of the new research, Posted this month In Geophysical Research Letters. “And that their observations of polar motion are accurate enough to see this effect.”

Earth’s axis has not moved enough to affect the seasons, which are determined based on the planet’s tilt. However, subtle patterns and changes in the planet’s rotation are very important to satellite 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.

It doesn’t look like it, but our planet’s rotation is nowhere near as smooth as the globe on your desk.

as it moves through space, The earth wobbles Like a badly thrown frisbee. This is partly because there is a bulge at the equator, and partly because air masses are circulating all the time in the atmosphere and splashing into the oceans. This is why the planet moves slightly from side to side.

Then there is this touring hub.

One of the main reasons is that the Earth’s crust and mantle are resurfacing after being covered by huge sheets of ice for thousands of years, so they now bounce like a mattress no one else lies on. This has constantly shifted the balance of masses around the planet.

at recent days, The balance was also disturbed Due to factors more related to human activity and global climate. Among them are the melting of mountain glaciers and ice sheets in Greenland and Antarctica, changes in soil moisture, and our storage of water in dams.

According to the study by Seo and colleagues, another important factor is groundwater depletion. In terms of influencing the Earth’s axis, groundwater pumping ranked second in magnitude between 1993 and 2010, behind only the post-Ice Age adjustment of the planet’s crust, according to the study.

There are other forces that could 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, Austin campus, and another author on the study. “For example, it is possible that something in the Earth’s outer core is also contributing,” he said.

However, this latest discovery opens up new possibilities for using information about the Earth’s rotation to study climate, Wilson said.

Because scientists have accumulated very precise data about the position of the Earth’s axis for most of the 20th century, they may be able to use it to understand changes in groundwater use that occurred before the most recent and reliable data were available.

Seo stated that he has already begun to study this possibility.

Raymond Chong Climate reporter. She joined The New York Times in 2017 and was part of the team that won the 2021 Pulitzer Prize in the public service category for coverage of the coronavirus pandemic. @employee