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Fluctuations in Earth’s liquid core are among the main culprits driving this trend, some astronomers tell the Star — but the climate crisis and human-driven landscape changes may factor in as well.

While it’s unlikely anyone would notice a missing millisecond, there’s potential this speed-up could have ramifications for our sensitive computer systems, the experts say. Here’s what you need to know.

Why is the Earth spinning faster?

One of the main drivers speeding up our planet’s spin is the Earth’s liquid core — a shifting sea of iron and nickel enveloping the innermost solid core, just below the mantle, explained Thomas Herring, a professor of geophysics at the Massachusetts Institute of Technology.

Data suggest this mass of metal has slowed in its convection in recent years, Herring said. As a result, the Earth’s rotation has sped up by a fraction to compensate, due to a physics principle known as the conservation of angular momentum.

“There has to be this balance,” Herring explained. “The momentum in the fluid core is big enough that it can explain these sort of fluctuations that we see over century time scales in the rotation of the Earth.”

A added that, since around 2010, the Earth’s solid inner core has also slowed in its rotation. Theoretically, this could also speed up each day by a fraction of a second.

Human-made changes to Earth’s surface may also play a role, said Ethen Sun, a graduate student studying astronomy and astrophysics at the University of É«É«À². “If you move mass closer to centre of earth, you’ll speed up the earth’s rotation. If you moved it away, it’ll slow down the earth’s rotation.”

For example, megabuildings have been shown to slow the Earth’s spin, with the Three Gorges Dam in China in particular estimated to add an  to the length of a day when it’s full.

Humans are slowing the Earth’s rotation in other ways as well. As the polar ice caps melt, raising sea levels and rebalancing the planet’s distribution of water and ice, it’s leading the planet to wobble — causing the planet’s rotation to slow and its axis to drift in location, .

Will the Earth’s rotation keep accelerating?

On Wednesday, the day will speed up by about 1.3 milliseconds. On July 22, the day will end 1.38 milliseconds earlier, and on August 5, a predicted 1.51 milliseconds will vanish from the clock.

It’s the latest development since 2020, when scientists discovered the . The shortest-ever recorded day happened just last year, when July 5 ended 1.66 milliseconds quicker than usual.

Herring believes the planet’s rotation has generally been speeding up since the 1970s, as a result of fluctuations in its core. But he doesn’t expect the trend to last.

Since around the dawn of our planet, Earth’s rotation has been gradually slowing down as a result of the moon. , the moon’s gravitational pull can cause water to bulge and shift, creating friction and fractionally slowing the Earth’s spin over the centuries.

Around one to two billion years ago, for example, .

Herring and Sun believe this slowing trend will continue after the Earth’s core returns to relative normalcy. , in about 200 million years, a day will last 25 hours instead of 24.

What does this mean for you?

You will mostly likely not notice the fractional speed-up of the Earth’s rotation. But our computer systems might.

That’s because, if the Earth keeps speeding up, we might have to remove a second from our time systems to keep our atomic clocks synced to the Earth’s rotation — a negative leap second.

“With modern computer systems, these leap seconds are actually causing all sorts of havoc,” Herring said. He recalled an incident where the addition of a leap second took an air traffic control system down in New Zealand for hours.

“Their air traffic controls system detected what it thought was an anomaly, and for safety, decided to shut the system down,” he said.

That’s when a second was added. We’ve never had a negative leap second before, Herring said, and our systems are not designed to handle it. Fortunately, it appears unlikely we’ll need to resort to this, as most scientists agree the Earth would go back to slowing down in its rotation in the near future, he said.

“Even when we do a positive leap second, it can cause problems with all of our modern communications because everything is so carefully synchronized,” he said. “Putting in a negative leap second would be really, really bad.”