The Earth is spinning too fast – the consequences for timekeeping could be unprecedented

Our home Planet is in a hurry. On June 29, 2022, Earth completed the shortest day since scientists began keeping records in the 1960s, completing a full rotation 1.59 milliseconds faster than usual.

Terrestrial 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 this record-breaking time of day of 29. 2022, 1.50 milliseconds earlier than planned.

We’re likely to see more record-breakingly short days if 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). The fact that the days on earth are getting shorter is no reason to worry, he says, because the actual time difference over the course of the year is fractions of a second. But the odd thing is that while scientists know that changes in the 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 intricate interior, each day isn’t exactly as long as the day before.

Also, a day of exactly 24 hours is just a standard we expect at the moment. Due to the gravitational pull of the moon on our earth, the earth’s rotation slows down in the long term. A few hundred million years ago, for example, a day on Earth lasted only 22 hours. In the coming millennia, an Earth Day will last much longer.

So what about the shorter days of late, bucking the long-term trend? One hypothesis that has been floated has to do with the “Chandler wobble”. Discovered in the 18th century, the phenomenon explains how the not-quite-perfectly-round Earth wobbles ever so slightly, like a spinning top, when it slows down. Leonid Zotov told timeanddate.com that the wobble mysteriously disappeared between 2017 and 2020, which could have helped Earth end the day a little quicker.

Another idea is that climate change could affect the planet’s rotation speed. When glaciers in the ocean melt, the shape of the earth changes slightly, becoming flatter at the poles and bulging at the equator. But Levine says that this effect can’t explain why the planet is suddenly spinning faster, because melting glaciers should have the opposite effect: the planet’s moment of inertia would increase, which would slow us down.

For Levine, the likely culprit is rather mundane.

“One of the possibilities is the exchange of momentum 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, when the atmosphere speeds up, the earth slows down.”

The same thing can happen deep in our world: it’s possible that the deep core and the mantle — the large layer that exists between the core and the surface — are moving at slightly different speeds. There could be an exchange of angular momentum between Earth’s deep core and the mantle, he speculates.

“These two effects… can either pump velocity into the Earth’s surface or take velocity out of the Earth’s surface,” says Levine. But the dynamics of the Earth’s atmosphere and interior are so complex that it is impossible, at least for now, to pinpoint any of these factors as a definite cause of the planet’s rapid speed.

Nature doesn’t always endure the rigidity of a clock or calendar, and planetary timepieces are used to making a few 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 rotation around the sun. As the day lengthens over time as the Earth’s rotational speed slows, timekeepers occasionally throw in a leap second to keep human time in sync with that of the solar system.

As the Earth accelerates, we face an unprecedented opportunity: the addition of a “negative leap second.” In other words, Levine says, if the planet continues to spin too fast, watchmakers may have to erase a full second by the end of the decade. For example, you could let the clocks jump 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 in the last year or two, Earth has definitely accelerated. And now, if that acceleration should continue – and there is a big one if there – then in about seven years, maybe eight, we might need a second negative lead.”

That has never happened before. Some scientists wonder if this could cause troubling hiccups in computer systems. However, given the way our world keeps surprising us, Levine isn’t yet convinced that the time will come.

“You should remember that this requires extrapolation over six years – and we’ve fretted about extrapolations before. So I wouldn’t be willing to bet the farm.”