Updated

Updated · Gizmodo · Jul 9

Timekeepers to Vote on Leap Hour in October as 30% Negative Leap-Second Risk Looms

Updated

Updated · Gizmodo · Jul 9

Timekeepers to Vote on Leap Hour in October as 30% Negative Leap-Second Risk Looms

Q: With a global vote looming, will our clocks soon be an hour out of sync with the sun's actual position?

No—our clocks will not soon be an hour out of sync with the sun, but international timekeepers are moving toward a system that would eventually allow that much drift before any correction. The vote expected at the General Conference on Weights and Measures in October 2026 would replace leap seconds with a “continuous UTC” system that can differ from Earth-rotation time, UT1, by as much as 3,600 seconds. The likely implementation date under the draft plan is May 20, 2027. That does not mean civil time will suddenly jump an hour next year. UTC is now kept within 0.9 seconds of UT1 by leap seconds, but those adjustments have repeatedly caused technical failures in telecoms, GPS, cloud services and finance. With Earth spinning unusually fast since 2020, experts warn a negative leap second may be needed as early as 2029, something many systems are poorly prepared to handle. BIPM’s Patrizia Tavella has said the risk of that happening before 2035 could be about 30 percent. The leap-hour approach is meant to avoid those disruptive one-second fixes by allowing UTC to drift gradually for a very long time—likely centuries—before any large correction is needed. So the practical effect in the near term is not that noon will stop matching the sun, but that official atomic time would be allowed to separate much more from astronomical time over generations. In short, the change would permit an eventual one-hour mismatch, not create one anytime soon.

2 articles · Updated · Gizmodo · Jul 9

October’s CGPM meeting will vote on replacing leap seconds with a leap hour, accelerating a decision that had been due by 2035.
A 30% risk of needing a negative leap second if authorities wait until 2035 has raised urgency, after Earth’s rotation began running unusually fast from 2016 onward.
July 4, 2024 set a record-short day at 1.66 milliseconds faster than normal, and experts say UTC could require a negative leap second as early as 2029.
Leap seconds were introduced in 1972 to keep UTC aligned with astronomical time, but they have caused technical problems in GPS, communications and banking systems, including a Cloudflare DNS failure tied to a 2017 leap second.
A leap hour would widen the adjustment margin and happen far less often, giving high-precision system operators more time to prepare for timekeeping changes.