Over the last couple of years, time has felt more nebulous than ever. You’d be forgiven for thinking that days are passing by at an increasingly faster clip. According to scientists, that perspective is not wrong. On June 29th, midnight arrived 1.59 milliseconds sooner than expected. It was the shortest day in over half a century, at least since scientists started tracking the pace of the Earth’s rotation with atomic clocks in the 1960s.
That wasn’t a one-off occurrence either. In 2020, the planet saw what were, at the time, the 28 shortest days in recorded history. And just last week, on July 26th, the day lasted 1.5 milliseconds less than usual. “Since 2016 the Earth started to accelerate,” Leonid Zotov, a researcher at Lomonosov Moscow State University, told CBS News. “This year it rotates quicker than in 2021 and 2020.”
Days have become much longer since the Earth’s formation. As The Guardian notes, around 1.4 billion years ago, a rotation of the Earth took less than 19 hours. Days have gotten longer by, on average, around one 74,000th of a second each year. But the planet’s rotation can fluctuate on a day-to-day basis.
Scientists believe there are a number of factors that may impact the Earth’s rotation, including earthquakes, stronger winds in El Niño years, icecaps melting and refreezing, the moon and the climate. Some have suggested the so-called “Chandler wobble” may have an effect on the rotation too. That phenomenon is a “small, irregular deviation in the Earth’s points of rotation relative to the solid Earth,” as USA Today puts it.
To account for fluctuations in the lengths of days, since 1972, there have been occasional leap seconds — a single-second addition to Coordinated Universal Time. Should the current trend of shorter days continue, there’s a possibility that a negative leap second may be needed to keep clocks aligned with the planet’s rotation. As such, UTC would skip a second.
Leap seconds already cause havoc on ultra-precise systems. Just last week, Meta called for an end to leap seconds, which have caused outages at Reddit and Cloudflare over the last decade. A negative leap second could lead to even more chaos.
“With the Earth’s rotation pattern changing, it’s very likely that we will get a negative leap second at some point in the future,” Meta engineers Oleg Obleukhov and Ahmad Byagowi wrote in a blog post. “The impact of a negative leap second has never been tested on a large scale; it could have a devastating effect on the software relying on timers or schedulers.”