The Earth is spinning so fast that it will soon lose a second

The changing rotation of the Earth threatens to upend our perception of time, clocks and computerized society in an unprecedented way, but only for a second.

For the first time in history, timekeepers around the world may have to consider subtracting a second from our clocks in a few years, because the planet is spinning a little faster than before. 

Clocks may need to skip a second - called a " negative leap second" - around 2029, according to a study published Wednesday in the journal Nature.

"This is an unprecedented situation and a major event," said the study's lead author, Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego. "It's not a huge change in the Earth's rotation that's going to cause a catastrophe or anything, but it's something notable. It's another indication that we're experiencing a very unusual time. "

Melting ice at Earth's two poles thwarted the planet's accelerating speed and likely delayed that second global assessment by about three years, Agnew said.

"We're heading toward a negative second," said Dennis McCarthy, weather director of the U.S. Naval Observatory, who was not involved in the study. “The question is when.”

This is a complex situation that involves physics, global power politics, climate change, technology and two types of weather. The Earth takes about 24 hours to rotate, but the keyword is "approximately".

For thousands of years, the Earth has been generally slowing down, with the rate varying from period to period, said Ms. Agnew and Judah Levine, a physicist in the National Standards Institute's Time and Frequency Division. and Technology (National Institute of Standards and Technology).

The slowdown is mainly due to the effect of tides, which are caused by the pull of the moon, McCarthy said. This didn't matter until atomic clocks were adopted as the official time standard more than 55 years ago. These have not slowed down.

Two versions of time - astronomical and atomic - were then created, but they did not correspond to each other. Every day, astronomical time lagged behind atomic time by 2.5 milliseconds. That means the atomic clock said it was midnight but for Earth it was midnight a fraction of a second later, Agnew said.

These daily fractions of seconds added up to whole seconds every few years. Starting in 1972, international timekeepers decided to add a "leap second" in June or December for astronomical time to catch up with atomic time, called Coordinated Universal Time (UTC). Instead of 11:59:59 at midnight, there would be an extra second at 11:59:60. A negative leap second would go from 11:59:58 directly to midnight, skipping 11:59:59.

Between 1972 and 2016, 27 separate leap seconds were added as Earth slowed down. But the pace of this slowdown has slowed. “In 2016, 2017 or maybe 2018, the rate of slowdown slowed to the point where the Earth started speeding up ,” Levine said.

Earth is speeding up because its hot liquid core - "a big ball of molten fluid" - acts unpredictably, with swirls and flows that vary, Agnew said.

According to Mr. Agnew, the core has been triggering an acceleration for about fifty years, but the rapid melting of ice at the poles since 1990 has masked this effect. Melting ice shifts the Earth's mass from the poles toward the domed center, slowing the rotation like an ice skater would by extending his arms out to the sides.

Without the effect of melting ice, the Earth would need this negative leap second in 2026 instead of 2029, Mr. Agnew calculated.

For decades, astronomers have managed to make universal time and astronomical time coincide thanks to these very practical little leap seconds. But computer system operators said those additions weren't easy to make given the precision of the technology the world relies on today. In 2012, some computer systems mishandled the leap second, causing problems for Reddit, Linux , Qantas Airlines and others, experts say.

“What’s the point of this time adjustment when it causes so much trouble?” , Mr. McCarthy said.

But Russia's satellite system relies on astronomical time, so eliminating leap seconds would cause problems for them, Mr. Agnew and Mr. McCarthy said. Astronomers and others wanted to retain the system that adds a leap second every time the difference between atomic time and astronomical time approaches one second.

In 2022, timekeepers around the world decided that starting in the 2030s, they would change the standards for inserting or removing a leap second, significantly reducing the likelihood of it.

Tech companies such as Google and Amazon have unilaterally implemented their own solutions to the leap second problem by gradually adding fractions of a second over an entire day, Mr. Levine said.

“The arguments are so serious because the stakes are so small ,” Mr. Levine said.

Then add the "bizarre" effect of subtracting, not adding, a leap second, Ms. Agnew said. It will likely be harder to skip a second because software is designed to add, not subtract, time, Mr. McCarthy said.

Mr. McCarthy said the trend toward needing a negative leap second is clear, but he thinks it has more to do with the fact that the Earth has become rounder due to geological changes at the end of the last ice Age.

Three other outside scientists said Agnew's study made sense and his evidence was compelling.

However, Mr. Levine doesn't think a negative leap second is really necessary. The general tidal slowing trend has been around for centuries and continues, he says, but shorter trends in the Earth's core come and go.

“This is not a process where the past is a good prediction of the future ,” Mr. Levine said. “Anyone who makes a long-term prediction about the future is on very, very shaky ground.”