Timekeepers to vote on ditching the leap second

Delegates from the International Bureau of Weights and Measures will vote in Versailles on whether to end the practice of inserting leap seconds into Coordinated Universal Time (UTC), a system used 27 times since 1972 to keep atomic clocks aligned with Earth's irregular rotation. Earth’s spin fluctuates because of the Moon’s tidal pull and short-term effects such as atmospheric changes, ocean currents, melting glaciers and volcanic or internal mass redistribution. Since the 1960s a second has been defined by cesium atomic transitions to meet the precision needs of systems like GPS, so leap seconds are now an occasional manual fix to reconcile atomic time with solar days; the last leap second occurred in 2016.

The leading proposal is to stop leap seconds and allow UTC to drift until a “leap hour” would be inserted only after centuries or millennia, avoiding recurrent one-second adjustments that have broken software and caused outages at major platforms. Engineers argue leap seconds violate common software assumptions and are increasingly risky, especially as Earth recently began speeding up - creating a potential need for a never-before-tested negative leap second. Opponents make philosophical arguments about disconnecting civil time from the solar day, but technologists point to new ultra-precise nuclear clocks and automated systems that will make a future leap hour manageable and remove the operational hassles of ad hoc second insertions.