BIPM Announces the End of the Leap Second by 2027
After three decades of debate in the metrological community, the leap second is officially coming to an end.
Radwan AbdulhadiEditor and technology writer
The End of an Obscure Metric
Leap seconds have driven a raging debate in the metrological community for three decades. Now, that argument has been put to rest: The leap second is officially dead, according to reporting by WIRED.
Doing away with an obscure metric the average person has been blissfully unaware of may seem like a novelty, but killing the leap second has major ramifications for technology you rely on every day. It also helps stave off what could've been a dangerous moment in time: The possibility of the world's first negative leap second.
Balancing Atomic and Astronomical Time
The International Bureau of Weights and Measurements, known by its French acronym BIPM, announced on Thursday that in May 2027 it would stop issuing leap seconds. A total of 32 leap seconds have been added since 1972 to adjust what is known as Coordinated Universal Time (UTC).
The world implemented the leap second in 1972 due to a growing gap between time measured with atomic clocks and time based on the Earth's rotation. The discrepancy occurs because the Earth's rotation is slowing down, driven in large part by tidal friction caused by the moon and the misalignment of Earth's rotation. The molten core of the planet, along with oceans and the atmosphere, also affects the spin rate.
Leap seconds function as a way to keep atomic-clock-driven UTC in line with astronomically kept Universal Time (UT1). Rather than happening on a set interval like a leap year, BIPM uses the average of hundreds of atomic clocks around the world and compares their time calculations to astronomical time to determine when a leap second is necessary. The most recent one was added in 2016.
Wreaking Havoc on Technology
Adding extra time is no small effort and presents a significant hassle for a single second. However, UTC remains vital for numerous APIs and databases. Introducing a leap second helped keep UTC and UT1 aligned, but it also wrought havoc on various systems running on UTC and forced companies to figure out how to deal with them when they were added every few years.
Major tech companies like Google and Meta have utilized a 'smear' method of dealing with leap seconds, spreading a leap second out over the course of a day in tiny increments, according to Judah Levine, a fellow at the US National Institute of Standards and Technology. However, these adjustments have frequently thrown off other systems. For example, the airline Qantas saw its booking system borked by a leap second in 2012.
The Threat of a Negative Leap Second
While adding a positive leap second proved difficult, the odds of having to add a negative leap second have been rising. This shift is partly because the Earth has picked up rotational speed in recent years due to climate change. Melting ice has caused a shift in the planet's gravity so extreme that a negative leap second may have been required as soon as 2029, according to a 2024 Nature study. Part of the calculus of ditching the leap second altogether was that going negative carried too much risk.
“There are continuing problems with positive leap seconds even after 50 years, and the concern was that the negative leap second would be much more serious because its effects had never been tested,” Levine notes.
BIPM time department director Patrizia Tavella confirmed these concerns, stating that the probability of a negative leap second convinced them to set the application date in 2027. She added that urgency increased following tests by an industry standards group that showed several failures with a negative leap.
Looking Forward to 2027 and Beyond
Tavella explained that the group selected May 20, 2027, for implementation because it marks the anniversary of the 1875 signing of the Metre Convention, which created BIPM, as well as Metrology Day.
The death of the leap second will simplify life for administrators and engineers alike. Tavella remarked that they will simply continue to accumulate seconds and normal minutes of 60 seconds, while Levine concurred that life will have one less hassle.
Although stopping leap seconds means atomic time and astronomical time will continue to drift apart, BIPM agreed to create a leap hour. Given the vast number of seconds in an hour, a leap hour remains millennia away. For now, systems relying on UTC require no further changes, leaving future generations to manage any larger discrepancies between UT1 and UTC.
Sources
- WIREDThe Leap Second Is No More
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