Our house The planet is in a hurry. On June 29, 2022, Earth completed the shortest day since scientists began keeping records in the 1960s, achieving a full rotation 1.59 milliseconds faster than usual.
The terrestrial rush is a trend. In 2020, the planet recorded the shortest 28 days on record and continued to spin rapidly through 2021 and 2022. Before scientists could even verify that record-setting day of June 29, our world nearly outdid itself: It burned through June 26. of July. 2022, 1.50 milliseconds ahead of schedule.
We’re likely to see more record short days as Earth continues to speed up, says Judah Levine, a professor at the University of Colorado-Boulder and a longtime expert at the National Institute of Standards and Technology (NIST). That Earth’s days are getting shorter is not cause for alarm, he says, because the actual time difference amounts to fractions of a second over the course of a year. But the strange thing is that while scientists know that changes to the Earth’s inner and outer layers, oceans, tides, and weather can affect the rate of rotation, they don’t know what’s driving the current rush.
Nobody is perfect – not even our planet. On average, the Earth rotates on its axis every 24 hours, or every 86,400 seconds. But for various reasons, from the imperfect shape of the planet to its complicated interior, every day is not exactly the same length as the day before.
Furthermore, a day that is exactly 24 hours long is simply a standard that we expect right now. The Earth’s rotation is slowing down in the long run thanks to the Moon’s pull on our world. Just a few hundred million years ago, for example, an Earth day was only 22 hours long. In the coming millennia, an Earth day will last much longer.
So what about the shorter days of the last few days, which contradict the long-term trend? One hypothesis that has been raised so far has to do with “Chandler wobble.” Discovered in the 1800s, the phenomenon explains how the Earth, which is not quite perfectly round, wobbles ever so slightly, like a top as it slows down. Leonid Zotov told timeanddate.com that the wobble had mysteriously disappeared between 2017 and 2020, which could have helped Earth get through the day a little faster.
Another idea is that climate change could affect the speed of the planet’s rotation. When glaciers melt into the ocean, Earth’s shape changes slightly, becoming flatter at the poles and bulging at the equator. But Levine says this effect can’t explain why the planet would suddenly spin faster because melting glaciers should have the opposite effect: The planet’s moment of inertia would increase, slowing us down.
For Levine, the likely culprit is more mundane.
“One of the possibilities is the exchange of momentum between the Earth and the atmosphere,” he says. “The sum of those two is a constant, which means, for example, that if the atmosphere slows down, the Earth speeds up. Or conversely, if the atmosphere speeds up, then the Earth slows down.”
The same thing can happen inside our world: the deep core and the mantle, the large layer between the core and the surface, may be moving at slightly different speeds. There could be an exchange of angular momentum between Earth’s deep core and mantle, he speculates.
“Both of these effects … can either pump speed up to the Earth’s surface or take speed away from the Earth’s surface,” says Levine. But the dynamics of the Earth’s atmosphere and interior are so complex that it’s impossible, at least now, to pinpoint one of these factors as the sure cause of the planet’s accelerated pace.
Nature doesn’t always adhere to the rigidity of a clock or a calendar, and planetary timekeepers are used to making some adjustments. A leap year, for example, exists because we need an extra day every four years to keep the 365-day calendar in sync with the Earth’s revolution around the Sun. Because the day gets longer over time as the As Earth’s rotation rate slows, timekeepers throw a leap second from time to time to keep human time in tune with the Solar System.
With the acceleration of the Earth, we are faced with an unprecedented possibility: adding a “negative leap second”. In other words, says Levine, if the planet continues to spin too fast, then by the end of the decade, the masters of the clock may need to erase a full second. For example, it is possible for clocks to move from 23:59:58 on December 31, 2029 to 00:00:00 on January 1, 2030.
“If you had asked me about the negative [leap second] Five years ago,” says Levine, “I would have said, ‘Never.’ But over the last year or two, the Earth is definitely speeding up. And now, if that acceleration were to continue, and there’s a big Yes there, then we might need a negative head start second in about seven years, maybe eight.”
This has never been done before. Some scientists wonder if doing so could introduce a worrying mishap into computer systems. However, given the way our world continues to surprise us, Levine still isn’t convinced the time is right.
“You should remember that that requires an extrapolation over six years, and we’ve been burned by extrapolations before. So, I wouldn’t be ready to stake the farm.”