Over the next few years, everyone on Earth will lose a second of time, but exactly when this happens is now affected by human-induced climate change.
For the first time in history, world timekeepers may have to consider subtracting a second from our clocks in a few years, as the planet spins a tad faster than it used to.
Clocks may have to skip a second – a so-called “negative leap second” – around 2029, according to a study in the journal Nature on Wednesday.
Without global warmingHowever, this time change would likely have occurred three years earlier, in 2026.
“This is an unprecedented situation and a major problem,” said study 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 will lead to a catastrophe or anything, but it is something remarkable. It’s another indication that we are in a very unusual time.”
How does global warming affect timekeeping?
If that had not been the case, the negative leap second should have come earlier global warmingsays the study.
“We’re heading towards a negative leap second,” said Dennis McCarthy, retired time director of the US Naval Observatory, who was not part of the study. “It’s a matter of when.”
The Earth is accelerating because its hot liquid core — “a big ball of molten fluid” — acts in unpredictable ways, with eddies and currents that vary, Agnew said.
He adds that the core has been accelerating for about 50 years, but the rapid melting of polar ice since 1990 has masked that effect.
Melting ice at both poles of the Earth due to human-induced climate change has slowed the planet’s rotation slightly. Less solid ice in the north and south and the resulting meltwater that raises sea levels shifts the planet’s mass toward the equator.
This slows down the rotation, just as a spinning skater slows down when he extends his arms out to the sides, Agnew said.
Without the effect of melting ice, the Earth would need that negative leap second in 2026 instead of 2029, according to his calculations.
How do we measure time?
Global timekeeping is a complex situation involving physics, global power politics, climate changetechnology and two types of time.
It takes about 24 hours for the Earth to rotate, but the key word is approximately.
For thousands of years, the Earth has been generally slowing down, with the speed varying from time to time, say Agnew and Judah Levine, physicists for the time and frequency division of the National Institute of Standards and Technology.
The slowdown is largely caused by the effect of the tides, which are caused by the moon’s gravitational pull, McCarthy said.
This didn’t matter until atomic clocks were adopted as the official time standard more than 55 years ago. They didn’t slow down.
That resulted in two versions of time – astronomical and atomic – and they didn’t match. Astronomical time lagged behind atomic time by 2.5 milliseconds every day. That meant the atomic clock would say it was midnight and for Earth it would be midnight a fraction of a second later, Agnew said.
Those daily fractions of seconds added up to whole seconds every few years.
Starting in 1972, international timekeepers decided to add a “leap second” to astronomical time in June or December to catch up with atomic time, called Coordinated Universal Time, or UTC. Instead of 11:59 and 59 seconds becoming midnight, there would be another second at 11:59 and 60 seconds.
A negative leap second would go from 11:59 and 58 seconds straight to midnight, skipping 11:59:59.
Between 1972 and 2016, 27 separate leap seconds were added as the Earth slowed down. But the pace of slowdown slowed.
“By 2016 or 2017 or maybe 2018, it had slowed down to the point where the Earth was actually accelerating,” Levine said.
Are these small time adjustments necessary?
For decades, astronomers have kept track of universal and astronomical time using those handy little leap seconds.
But computer systems administrators said these additions aren’t easy because of the precise technology the world now relies on. In 2012, some computer systems mishandled the leap second, causing problems for Reddit, Linux, Qantas Airlines and others, experts say.
“What is the need for this adjustment in time if it causes so many problems?” McCarthy said.
But that of Russia satellite system depends on astronomical time, so eliminating leap seconds would cause problems, Agnew and McCarthy said. Astronomers and others wanted to keep the system that would add a leap second when the difference between atomic and astronomical time approached one second.
In 2022, the world’s timekeepers decided that starting in the 2030s, they would change the standards for inserting or removing a leap second, making this much less likely.
Technology companies like Google and Amazon have unilaterally come up with their own solutions to the leap second problem by gradually adding fractions of a second over an entire day, Levine said.
“The fighting is so serious because the stakes are so small,” Levine said.
Then add the “weird” effect of subtraction, and no leap second, Agnew said. It’s probably harder to skip a second because software programs are designed to add time, not subtract it, McCarthy said.
McCarthy said the trend toward needing a negative leap second is clear, but he thinks it has more to do with the Earth becoming rounder due to geological shifts since the end of the last century. ice age.
Three other outside scientists said Agnew’s research makes sense and called his evidence compelling.
But Levine doesn’t think a negative leap second will really be necessary. He said the overall slowing trend is out tides has been around for centuries and continues, but the shorter trends in the Earth’s core come and go.
“This is not a process where the past is a good predictor of the future,” Levine said. “Anyone who makes a long-term prediction about the future is on very, very shaky ground.”