Around the turn of the millennium, the rotation of the earth began to change and no one quite knew why.
For decades, scientists had watched the average position of our planet’s axis of rotation, the imaginary rod around which it spins, gradually move away from the geogrhic North Pole and toward Canada. But, suddenly took a sharp turn and started heading east.
Over time, the investigators came to a startling conclusion about what had hpened. The accelerated melting of the polar ice cs and mountain glaciers had changed the way mass was distributed across the planet enough to influence its rotation.
Now, some of the same scientists have identified another factor which has the same kind of effect: colossal amounts of water drawn from the soil for crops and homes.
“Wow,” Ki-Weon Seo, who led the research that led to the latest discovery, remembers thinking when his calculations showed a strong relationship between groundwater extraction and the drift of the Earth’s axis. It was a “big surprise,” said Seo, a geophysicist at Seoul National University.
Water experts have long warned against the consequences of overexploitation of groundwaterespecially as water from underground aquifers becomes an increasingly vital resource in drought-stricken areas such as the western United States.
When groundwater is extracted but not replenished, the land can subside, damaging homes and infrastructure and also reducing the amount of space below ground that can hold water later.
Between 1960 and 2000, worldwide groundwater depletion doubled, reaching nearly 300 billion cubic meters per year, scientists estimate.
Since then, satellites that measure variations in Earth’s gravity have revealed the staggering magnitude of depletion of groundwater supplies in certain regions, such as India and the Central Valley of California.
“I’m not surprised that it has an effect” on Earth’s rotation, said Matthew Rodell, an Earth scientist at NASA’s Goddard Space Flight Center.
But “it’s impressive that they were able to deduce it from the data,” he added, referring to the authors of the new research, published this month in the journal Geophysical Research Letters. “And that the observations they have of polar motion are precise enough to see that effect.”
The consequences of the twist
Earth’s axis hasn’t moved far enough to affect the seasons, which are determined by the planet’s tilt. But the delicate patterns and variations in the planet’s rotation are hugely important for satellite navigation systems that guide planes, missiles and m plications. This has led researchers to try to understand why the axis is moving and where it might be heading.
It is not felt, but the rotation of our planet is not at all as smooth as that of the terrestrial globe that we have on the table.
As you move through space, the earth wobbles like a mis-thrown frisbee. This is partly because it bulges at the equator, and partly because air masses are constantly swirling in the atmosphere and water churning in the oceans, pulling the planet slightly from side to side.
And then there is the issue of axis deviation.
One of the main causes is that the Earth’s crust and mantle are returning to their original she after having been covered for millennia by gigantic sheets of ice and recovering volume like a mattress from which a sleeping person has risen. This has been constantly changing the mass balance across the planet.
More recently, the balance has also been upset by factors more closely linked to human activity and global climate. These include the melting of mountain glaciers and the Greenland and Antarctic ice sheets, changes in soil moisture, and the accumulation of water in dams.
Another important factor, according to the study by Seo and his colleagues, is the reduction of groundwater. Regarding the effect on the Earth’s axis, the extraction of subsoil water was the second factor in magnitude between 1993 and 2010, only surpassed by the adtation of the planet’s crust after the age of glaciers, according to the study.
According to Clark R. Wilson, a geophysicist at the University of Texas at Austin and another of the study’s authors, there are other forces that could be pushing Earth’s axis in its new direction, but they’re not yet fully understood. “It’s possible, for example, that there is something in Earth’s fluid core that is also contributing,” he said.
However, the latest discovery suggests new possibilities for using information about the Earth’s rotation to study climate, according to Wilson.
Since scientists have collected very precise data on the position of the Earth’s axis for much of the 20th century, they could use it to understand changes in groundwater use that took place before the most modern data became available. and reliable.
Seo said he has already started looking into that possibility.
Source: The New York Times
Translation: Elisa Carnelli