RIP Leap Second: Time Fix to Be Scrapped by 2035

Scientists and government representatives last week agreed to retire the practice of adding leap seconds to make up for the difference between exact atomic time and Earth's slower rotation.

A vote, held Friday at the General Conference on Weights and Measures (GCWM) in Paris, means the (eventual) end of a 50-year tradition used to fix discrepancies between atomic time and observed solar time. Leap seconds are still on the table until 2035 at the latest, The New York Times reports.

Though unnoticed by most people, the occasional one-second adjustment can cause problems for systems that require an exact, uninterrupted flow of time. Reddit, for instance, was down for 40 minutes in 2012 when a leap second confused the company's servers; four years later, Cloudflare's DNS services were interrupted due to the miniscule time change.

There's still plenty of time for satellite navigation, telecommunications software, and even space travel to be disrupted by the addition of leap seconds. After 2035, though, the difference between atomic and astronomical time will be allowed to grow to a larger, yet-to-be-determined value.

Since their introduction in 1972, 27 leap seconds have been added to Coordinated Universal Time (UTC)—most recently on Dec. 31, 2016.

Because Earth's rotation speed varies based on climate and geological events, leap seconds are irregularly spaced and often unpredictable. Usually decided about six months in advance, they are used to ensure the difference between UTC and observed solar time (UT1) readings never exceed 0.9 seconds.

"Recent observations on the rotation rate of the Earth indicate the possible need for the first negative leap second whose insertion has never been foreseen or tested," says the 27th GCWM program.

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"The accepted maximum value of the difference (UT1-UTC [known as DUT1]) has been under discussion for many years," the document said. It blames the introduction of leap seconds for "discontinuities that risk causing serious malfunctions in critical digital infrastructure including the Global Navigation Satellite Systems (GNSSs), telecommunications, and energy transmission systems."

This summer, Facebook and Instagram parent company Meta called for the removal of leap seconds, calling it "equally bad for both digital applications and scientists," and "a risky practice that does more harm than good."

"As engineers at Meta, we are supporting a larger community push to stop the future introduction of leap seconds and remain at the current level of 27, which we believe will be enough for the next millennium," production engineer Oleg Obleukhov and research scientist Ahmad Byagowi wrote in a July blog post.