The General Conference on Weights and Measures (CGPM), at its 28th meeting in 2026, has adopted a resolution on the technical steps needed to keep Coordinated Universal Time (UTC) continuous. UTC is produced by the International Bureau of Weights and Measures (BIPM) and differs from International Atomic Time (TAI) only by an integral number of seconds. It is the recommended reference for international time and the basis of civil time in most countries.
In 2022, the CGPM decided to increase the maximum allowed difference between UTC and the Earth's rotation time scale (UT1) by 2035, in order to ensure UTC continuity for at least a century. Industrial users and national critical infrastructures, including transportation, energy distribution, telecommunications and space projects, require UTC to run without future adjustments. Some software systems also need a fixed maximum value for the difference |UT1-UTC| to be designed correctly.
Experts at a March 2025 workshop organized by the Consultative Committee for Time and Frequency (CCT F) and the International Earth Rotation and Reference Systems Service (IERS) estimated that the probability of a negative leap second will rise rapidly, reaching 30 % by 2035. A negative leap second has never been applied and is considered a high risk for critical infrastructures that are largely unprepared. Preparing for it would require significant financial investment across time-dependent industries, a cost estimated to be similar to preparations for the millennium bug.
The growing use of Internet of Things devices, smart grids and distributed systems increases the risk of malfunction whenever a leap second is inserted, especially a negative one. Different mitigation methods used by global service providers have also led to timing inconsistencies between systems, which do not conform to the SI unit. The resolution aims to address these risks before they become urgent.
Source: Hacker News · Summarized by HeadlinesBriefing