By Evan Bush—
NBC News
Global warming has slightly slowed the Earth's rotation, which could affect how we measure time.
According to a study published this Wednesday, the melting of the poles – a trend that is accelerating mainly due to the climate crisis caused by humans – has caused the Earth to rotate less quickly than it would otherwise.
Study author Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego, said that as ice at the poles melts, it changes where Earth's mass is concentrated. The change, in turn, affects the angular velocity of the planet.
A midnight sun near the Kangerlussuaq ice sheet, where brown sediment in the ice is created by rapid melting.Martin Zwick / REDA&CO/Universal Images Group via Getty Images
Agnew compared the dynamics to that of a figure skater spinning on ice: "If a skater starts spinning, if she puts her arms down or straightens her legs, she will slow down," he explained, "but if the skater puts her arms in, she will spin more." fast".
Less solid ice at the poles means more mass around the equator, the waist of the Earth.
“What happens with melting ice is that frozen water in places like Antarctica and Greenland melts and moves the fluids to other places on the planet,” said Thomas Herring, a professor of geophysics at the Massachusetts Institute of Technology, who was not involved in the study. new study: “Water flows toward the equator.”
The study suggests, in other words, that human influence has manipulated a force that astronomers and scientists have wondered about for millennia, something that was long considered a constant outside of humanity's control.
“It's impressive, even to me, that we've done something that measurably changes the speed at which the Earth spins,” Agnew said, “things are happening that are unprecedented.”
Their study, published in the journal Nature, suggests that the climate crisis is playing a large enough role in the Earth's rotation to delay the possibility of a "negative second leap." If the polar ice had not melted, clocks around the world might have needed to subtract a single second as early as 2026 to keep universal time synchronized with the Earth's rotation, which is influenced by several factors.
However, the effect of the climate crisis has delayed that possibility by about three years. If timekeeping organizations eventually decide to add a negative leap second, the adjustment could disrupt computer networks.
The reason leap second adjustments are necessary is that, even without climate change, the Earth's daily rotation has tended to slow down over time, even though it appears constant.
About 70 million years ago, days were shorter and lasted about 23.5 hours, a study published in the journal Paleoceanography and Paleoclimatology suggested. This means that the Cretaceous dinosaurs lived on a planet with 372 days a year.
[Global warming has caused biodiversity on the planet to decrease by 69%]
Several factors affect the spin of the planet, sometimes in opposition.
Ocean tidal friction, due in part to the Moon's gravitational pull, slows the Earth's rotation. Meanwhile, since the last ice age, the Earth's crust has been rising in some regions in response to the retreating weight of ice sheets. This effect modifies the distribution of mass and accelerates the planet's spin. Both processes are fairly constant and have predictable rhythms.
Another factor is the movement of fluids in the Earth's liquid inner core, a wild card that can speed up or slow down the speed of Earth's rotation, according to Agnew.
Now polar melting has been added to the mix. As climate change intensifies, researchers predict it will have a more profound effect on the way the planet rotates.
“Their contribution will be greater as time goes on and the melting accelerates, as we expect it will,” Herring said. He added that the new study was a comprehensive and robust analysis
that combined research from several disciplines of science.
The need for timekeepers to adjust universal time to keep it in line with the Earth's rotation is not a new phenomenon. But historically, that has meant adding leap seconds to the common standard of clocks, because the slowing of the Earth's spin causes astronomical time to lag behind atomic time (which is measured by the vibration of atoms in clocks). atomic).
In recent decades, however, the Earth has rotated faster than would be expected due to fluctuations in its core. This has led timekeepers to consider—for the first time since Coordinated Universal Time was officially adopted in the 1960s—whether it would make sense to subtract a leap second to keep universal time at the same rate as the Earth's rotation.
The melting of the polar ice has counteracted this trend and has brought forward any decision on a negative leap second. According to Agnew's estimates, it has delayed that possibility by three years, from 2026 to 2029, if the current rate of Earth's rotation is maintained.
Adding and subtracting leap seconds is a nuisance because it can disrupt satellite transmission, financial and energy systems, which depend on extremely precise timing. That's why world timekeepers voted in 2022 to abolish leap second additions and subtractions by 2035 and let universal time move away from the Earth's rotation rate.
“Since approximately the year 2000, emphasis has been placed on the elimination of leap seconds,” said Agnew.
Whether the clocks end up changing or not, the idea that the melting of the poles affects the Earth's rotation shows how important this issue has become. Research has already outlined the profound impact ice loss will have on coastal communities.
Scientists expect sea level rise to accelerate as the climate warms, a process that will continue for hundreds of years. Last year, leading polar researchers warned in a report that parts of the major ice sheets could collapse and that coastal communities should prepare for many feet of sea level rise. If humanity allows the global average temperature to rise by two degrees Celsius, the planet could face a sea level rise of more than 40 feet.