Melting polar ice slows Earth's rotation and can affect time

Global warming has slowed the Earth's rotation slightly—and that could affect the way we measure time.

Melting polar ice — a rapid trend driven primarily by human-caused climate change — has caused the Earth to spin slower than it otherwise would, a study published Wednesday found.

Duncan Agnew, a geophysicist at the University of California San Diego's Scripps Institution of Oceanography, said that as the ice at the poles melts, it shifts where Earth's mass is concentrated. The transition affects the angular momentum of the planet.

Agnew compared the dynamic to a figure skater spinning on ice: “If you have a skater start to spin, if she lowers her arms or extends her legs, she'll slow down,” he said. But if the skater's arms are pulled inward, the skater spins faster.

Less solid ice at the poles means more mass around the equator – around Earth's waist.

“You're taking frozen water that's frozen in places like Antarctica and Greenland, and the frozen water is melting, and you're moving the fluids to other places on the planet,” Thomas Herring said. A professor of geophysics at the Massachusetts Institute of Technology who was not involved in the new study. “Water flows toward the equator.”

In other words, the study suggests that humans influence apes with a force that scholars, astrologers, and scientists have puzzled over for thousands of years — a force long considered static beyond humanity's control.

“It's kind of interesting, even to me, that we've measurably changed how fast the Earth is spinning,” Agnew said. “Unprecedented things are happening.”

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His study, published in the journal Nature, suggests that climate change is playing a significant enough role to counteract the opposite trend in Earth's rotation. Due to a combination of factors, Earth has begun to spin faster in recent decades, a temporary trend that has prompted scientists for the first time to consider subtracting a “negative leap second” from clocks worldwide in 2026. But the melting polar ice has delayed that possibility by about three years, according to Agnew's estimate.

If timekeeping organizations eventually decide to add a negative leap second, the adjustment will disrupt computer networks.

A view of Earth captured by a deep space climate monitoring satellite.NASA

Historically the reason leap second correction is needed is that even without climate change, Earth's diurnal rotation has slowed over millions of years, even if it appears constant.

A study suggests that about 70 million years ago, days were shorter and lasted about 23.5 hours. Paleoceanography and paleoclimatology suggest. That means Cretaceous dinosaurs experienced a planet with 372 days each year.

Many important factors influence the rotation of the planet – sometimes working in opposition.

The friction of ocean waves due 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 areas in response to the weight of the ice sheets being removed. That effect changes where mass is distributed and accelerates the planet's rotation. Both of those processes are very stable and have predictable rates.

Another factor is the movement of fluid within Earth's liquid inner core — which can speed up or slow down how fast Earth spins, Agnew said. Fluctuations in Earth's core are the primary reason the planet has rotated faster than expected in recent decades.

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That fast spin has led timekeepers to consider whether it makes sense to subtract a leap second to keep universal time in lock with Earth's rotation — for the first time since unified universal time was officially adopted in the 1960s.

But melting polar ice bucks that trend and precludes any conclusion on whether to add a negative leap second. According to Agnew's estimate, the current pace of Earth's rotation has delayed that possibility to 2026 to 2029.

As climate change intensifies, researchers expect melting ice to have an even more profound effect on how the planet spins.

“It's going to have a bigger contribution as time goes on, and we expect that as the melt speeds up, we might do that,” Herring said. He said the new study is a thorough, robust analysis that integrates research from many fields of science.

The need for timekeepers to adjust universal time to the Earth's rotation is not a new phenomenon. But historically, the common standard for clocks involved adding leap seconds when Earth's fast rotation pushed astronomical time back to atomic time (which is measured by the vibrations of atoms in atomic clocks).

Adding or subtracting leap seconds is painful because they have the potential to disrupt satellite, financial and energy transmission systems that rely on highly accurate timing. because that Timekeepers worldwide voted to eliminate the leap second in 2022 By 2035 add and subtract and let universal time drift away from the speed of Earth's rotation.

“There's been a push since 2000 to get rid of leap seconds,” Agnew said.

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Regardless of whether the clocks change, the idea that melting polar ice is affecting the Earth's cycle speaks to how important an issue it has become. Research has already described the profound impact ice loss has on coastal communities.

Scientists expect sea level rise to accelerate as the climate warms, continuing for hundreds of years. Last year, high polar researchers warned in a report that parts of major ice sheets could collapse and that coastal communities should prepare for several feet of sea level rise. If humanity allows the average global temperature to increase by 2°C, the planet will commit to more than 40 feet of sea level rise.

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