Metrology scientists gathering in Versailles this week are voting to accelerate the permanent phase-out of the "leap second" to May 2027, brought forward from ... a previous deadline of 2035.
The periodic addition of a 61st second to Coordinated Universal Time (UTC) has been used since 1972 to align atomic time with the Earth's variable rotation. However, digital systems, financial markets, satellite navigation networks, and telecommunication grids struggle to process the irregular time adjustment.
When a leap second is inserted, digital clocks transition from 23:59:59 to 23:59:60 before resetting to 00:00:00 - a non-standard sequence that triggers computer crashes, server loops, and service outages across global infrastructure.
Threat of the 'negative leap second'
While 27 positive leap seconds have been added since 1972 - most recently on 31 December 2016 - recent observations show the Earth's rotation is accelerating. This physical shift introduces the threat of a "negative leap second" - where a clock would skip from 23:59:58 directly to 00:00:00.
"We consider this measure necessary given the significant risks posed by introducing a negative leap second for the first time," explained Dolores del Campo Maldonado, director of mechanical engineering at the Spanish Metrology Centre (CEM).
A negative leap second has never been tested in live IT environments, raising fears of widespread failure across global software systems, banking networks, and GPS navigation.
New one-hour threshold for future corrections
Under the proposal being voted on by the General Conference on Weights and Measures, the tolerance threshold between atomic time and astronomical time will be expanded to one hour.
This change means atomic clocks will run continuously without micro-adjustments for centuries, until the cumulative drift between Earth's rotation and atomic time reaches 60 minutes, at which point a single planned hour correction will occur.
Metrologists noted that establishing a unified, continuous time scale is also essential for future space exploration, as international space agencies prepare to establish a standardised lunar time zone for upcoming moon missions.