Time lords prepare to kick leap seconds into the next millennium

A vote by the General Conference on Weights and Measures next month could put an end to leap seconds, a practice that has been added to Coordinated Universal Time (UTC) since 1972. The conference is considering a proposal that would make UTC continuous from May 20, 2027, and allow the difference between UTC and UT1, a measure based on Earth's rotation, to reach up to an hour.

Leap seconds were introduced to keep UTC within 0.9 seconds of time determined by Earth's slightly wobbly rotation. Since their inception, 27 leap seconds have been added. However, recent increases in Earth's rotational speed have raised the possibility of a negative leap second, meaning a second would be removed rather than added.

This would be the first time such an adjustment has been attempted. Experts estimate a 30 percent probability that a negative leap second would be needed by 2035. The primary concern is that many computer systems were designed assuming leap seconds would always be added, which could lead to severe disruptions in critical infrastructure like telecommunications, electricity grids, and satellite navigation systems.

To mitigate these risks, the proposal suggests allowing UTC to diverge from rotational time by up to an hour, eliminating the need for further leap-second adjustments for many years. While this likely will not occur for at least a thousand years, most national delegates at the conference have been eager to end leap seconds due to the associated risks.