Metrology conference to vote on ending leap seconds in UTC
The General Conference on Weights and Measures is expected to vote on ending the use of leap seconds to keep Coordinated Universal Time (UTC) closely aligned with Earth’s rotation. The change would reduce the risk of computer and infrastructure problems caused by adjusting clocks, particularly if a negative leap second were needed.
Since 1972, 27 seconds have been added to UTC to keep it within 0.9 seconds of the astronomical time scale UT1. The proposal would allow the difference to grow to as much as one hour, avoiding adjustments for centuries; experts estimate a 30 per cent chance that systems will need a negative leap second by 2035. If approved, the change would take effect on 20 May 2027, while UT1 would continue to be monitored and its difference from UTC published.
- Global timekeepers are expected to vote to end leap seconds.
- UTC could differ from Earth-based UT1 by up to an hour.
- The change could take effect on 20 May 2027.
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UTC is the standard time used for clocks around the world and for many computer systems. Earth’s rotation is not perfectly steady, so UTC has sometimes been adjusted to stay close to UT1, a time scale based on the planet’s rotation.
Since 1972, 27 leap seconds have been added to UTC. Adjusting clocks can cause problems for computer systems and infrastructure, and experts say a negative leap second, which would require clocks to skip a second, could be needed in the coming years.
The General Conference on Weights and Measures brings together representatives of countries to agree international standards. The proposed change would let UTC drift further from UT1 while continuing to measure and publish the difference, affecting how closely civil time tracks Earth’s rotation.
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The case for
Ending leap seconds would make timekeeping more predictable for digital systems and infrastructure, which can be disrupted by sudden clock adjustments. The risk is especially concerning because a negative leap second has never been implemented; allowing UTC to drift from Earth’s rotation would avoid such changes for centuries while continuing to publish the difference for those who need it.
The case against
Keeping UTC closely aligned with Earth’s rotation preserves a clear connection between civil time and the natural day, which matters for applications that rely on solar or astronomical time. Allowing the gap to grow substantially could complicate those uses and shift the burden to systems that need to track or correct for the difference, even if publishing it helps them do so.
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Originally published by The Register as “Leap seconds face judgment day as time lords prepare to vote”.