International bodies set to vote on ending leap seconds in timekeeping

The International Bureau of Weights and Measures (BIPM) is scheduled to vote on a resolution that would discontinue the use of leap seconds, a correction added to Coordinated Universal Time (UTC) to keep it in sync with Earth's irregular rotation. If approved, the change would become operational in May 2027.

Leap seconds have been inserted 27 times since 1972 to reconcile astronomical time, based on Earth's spin, with the highly stable atomic clocks that define UTC. The practice has caused occasional disruptions for data servers, financial trading platforms and other systems that require precise timing, prompting major technology firms to call for its removal.

"We have to make a choice on whether the most important thing is a sense of time given by objects in the sky directly above, say, the Greenwich longitude, or you decide to follow what you believe are more stable, laboratory, man-made clocks," said Jeff Sherman, group leader of the National Institute of Standards and Technology's Time and Frequency Division.

BIPM director Patrizia Tavella noted that the correction has become a serious issue for modern applications and that the organization has been discussing a shift to Continuous Coordinated Universal Time for more than two decades. She added that the proposed resolution would allow atomic time to drift from astronomical time, with a maximum allowable difference of one hour, a gap that would take millennia to reach.

Some experts caution against eliminating the leap second. Marek Ziebart, a professor of space geodesy at University College London, argued that the existing system works and that removing the adjustment would require extensive software changes. He also emphasized the cultural and scientific value of maintaining a timescale linked to Earth's rotation.

The vote comes amid concerns that future variations in Earth's rotation could eventually require a "negative" leap second—subtracting a second from UTC. BIPM warned that critical infrastructure is largely unprepared for such a scenario, likening the required investments to those made for the Y2K transition.

If the resolution passes, the shift would be largely invisible to the public, with daily routines and circadian rhythms expected to remain unchanged, according to Louise Devoy, senior curator of the Royal Observatory Greenwich.