Member states replace leap seconds with a future leap hour

Most people will not notice the change, Philippe Richard says

Member states at the General Conference on Weights and Measure have decided to abandon leap seconds and introduce a leap hour, according to Philippe Richard, director of the Swiss Federal Institute of Metrology. Richard spoke with NPR host Scott Simon in an interview published October 24, 2026, after the conference met in Versailles near Paris.

The decision addresses a basic mismatch in timekeeping. A nominal day is 24 hours, but the Earth’s spin has slowed slightly, leaving one rotation at 24 hours plus some microseconds. Leap seconds have allowed the atomic timescale to remain aligned with astronomical time as the difference accumulates.

Richard used two watches to explain the problem: an old Swiss mechanical watch represented the Earth, while a modern, precise quartz watch represented atomic time. He said the quartz watch would gradually diverge from the mechanical watch and need correction by seconds or minutes, much as atomic time is corrected to follow Earth’s rotation.

Richard said leap seconds have been used since 1972, with 27 introduced at an average of one every two years. As the Earth slows, the gaps between the astronomical and atomic timescales would otherwise keep growing.

At the conference, member states chose a different unit for future adjustments: one hour rather than one second. Richard said the change could delay an hour-long correction until probably between 4,000 and 7,000 years.

“Just to put it very simply, introducing a leap hour instead of a leap second is to pass the problem on the future generation,” Richard said. The decision changes the size and frequency of future corrections rather than the everyday precision required from timekeeping systems.

Richard said the new approach would have no noticeable effect on ordinary daily life. The previous 27 leap seconds went unobserved, he said, and people would likewise not realize the change. “Not at all. We will not realize the change,” he said.

The continued need for precision is separate from whether people notice the adjustment. Richard said synchronization is becoming increasingly important for power grids and electricity networks, computer networks and satellite positioning. He confirmed that metrology is the study of measurement and said these systems depend on its infrastructure of very precise measurements.

Scott Simon asked whether exact time matters in everyday life despite the invisibility of the change. Richard said precision was extremely important and that people benefit when infrastructure works correctly. The policy shift itself would go largely unnoticed, he said, while the measurement systems supporting electricity, computing and satellite positioning remained essential.