Ground rush is a trend. In 2020, the planet recorded its 28 shortest days on record, and it continued to spin rapidly in 2021 and 2022. Before scientists could even verify that record time on June 29, our world almost outdid itself: Blaze up on July 26. 2022, 1.50 milliseconds ahead of schedule. We’ll likely see more record days as Earth continues to accelerate, 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 isn’t a cause for concern, he says, because the actual time difference amounts to fractions of a second over the course of a year. But what’s strange is that while scientists know that changes in Earth’s inner and outer layers, oceans, tides and climate can affect how fast it spins, 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 a variety of reasons, from the planet’s imperfect shape to its complex interior, each day isn’t exactly the same length as the day before. Furthermore, a day lasting exactly 24 hours is just a standard we currently expect. The Earth’s rotation slows 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 does it do with the shorter days of late, which lower the long-term trend? One hypothesis that has been put forward so far has to do with the “Chandler swing”. Discovered in the 1800s, the phenomenon explains how the not-perfectly-round Earth wobbles ever so slightly, like a spinning 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 end the day a little faster. Another idea is that climate change may affect the planet’s rotation speed. When glaciers melt into the ocean, the shape of the Earth changes slightly, becoming flatter at the poles and bulging at the equator. But Levine says this phenomenon can’t explain why the planet would suddenly spin faster, because the melting glaciers would have the opposite effect: the planet’s moment of inertia would increase, which would slow us down. For Levine, the likely culprit is more mundane. “One possibility is momentum exchange between the Earth and the atmosphere,” he says. “The sum of these two is a constant, which means, for example, if the atmosphere slows down, then the Earth speeds up. Or conversely, if the atmosphere speeds up, then the Earth slows down.” Universal History Archive/Universal Images Group/Getty Images The same thing can happen deep inside our world: It’s possible for the deep core and the mantle—the large layer that exists between the core and the surface—to move at slightly different speeds. There could be an exchange of angular momentum between the Earth’s deep core and the mantle, he speculates. “Both of these effects … can either pump velocity into the Earth’s surface or remove velocity from the Earth’s surface,” says Levine. But the dynamics of Earth’s atmosphere and interior are so complex that it is impossible, at least at this time, to point to one of these factors as the sure cause of the planet’s rapid pace. Nature does not always adhere to the rigidity of a clock or a calendar, and planetary chronometers are accustomed to make some modifications. 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 rotation around the Sun. Because the day grows longer over time as the Earth’s rotation speed slows, timekeepers drop a leap second every so often to keep human time in line with the Solar System. With the Earth accelerating, we face 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 clocks may need to erase a full second. For example, they may skip clocks from 23:59:58 on December 31, 2029 to 00:00:00 on January 1, 2030. “If you asked me about the negatives [leap second] five years ago,” says Levine, “I would have said, ‘Never.’ But in the last couple of years, the Earth has definitely been speeding up. And now, if that acceleration were to continue — and there’s a big if — then we could need a second negative lead in about seven years, maybe eight.” This has never happened before. Some scientists wonder if this could create a problematic hiccup in computer systems. Given the way our world continues to surprise us, however, Levine isn’t yet convinced that time will come. “You have to remember, this requires an extrapolation over six years — and we’ve been burned before on extrapolations. So I wouldn’t be ready to bet the farm.” LEARN SOMETHING NEW EVERY DAY.
