Security risk: Why the leap second will soon be abolished

The world’s timekeeping system is set for a major overhaul. The General Conference on Weights and Measures (CGPM) has decided that starting May 20, 2027, the leap second will be abolished. This decision comes after years of deliberation over the risks posed by these adjustments to atomic clocks and the Earth's rotational speed. Leap seconds have been used since 1972 to keep Coordinated Universal Time (UTC), based on atomic measurements, aligned with astronomical time (UT1), which depends on the Earth’s rotation. The CGPM aims to eliminate potential disruptions in critical infrastructure such as energy supply, telecommunications, and transportation by ensuring a continuous UTC without sudden one-second corrections. The current system relies on two distinct bases for measuring time. UTC is derived from atomic clocks, providing a highly stable reference. In contrast, UT1, or Universal Time, is determined by the Earth’s rotation, which varies slightly due to factors such as seasonal changes, tidal forces from the Moon and Sun, and internal planetary movements. These variations mean the two timescales diverge slightly over time. To prevent this divergence from exceeding 0.9 seconds, a leap second has been added at irregular intervals, most recently in December 2016. Since 1972, 27 such adjustments have occurred, each inserted either at the end of June or December, creating minutes with 61 instead of 60 seconds. The CGPM’s decision follows concerns about the possibility of a negative leap second, a scenario in which a second would need to be subtracted rather than added. This situation has never occurred before, and its implementation could pose unforeseen technical challenges. Industry representatives have warned that such a change might require extensive preparation and incur additional costs. According to the conference, the likelihood of needing a negative leap second in the coming years has increased, prompting the move to abolish the practice altogether. Under the new proposal, UTC will be allowed to differ from UT1 by up to 3,600 seconds, equivalent to one hour, for several centuries. Scientists hope this adjustment will reduce the frequency of necessary recalibrations. Some software systems require a defined maximum deviation, making this approach more practical for long-term stability. While the difference between UTC and UT1 will grow gradually, the impact on everyday life is expected to remain minimal for many years. Current legal time already differs from local solar time due to time zones, geographic location, and daylight saving adjustments. The change is likely to affect professionals who rely on astronomical time, such as astronomers and geodesists involved in mapping the Earth’s surface. For the general public, the shift should go unnoticed, as modern devices and systems already account for discrepancies between official time and solar time. The CGPM’s decision marks a significant step toward simplifying global timekeeping while addressing growing concerns about the reliability of existing methods.