Time lords prepare to kick leap seconds into the next millennium
Global timekeeping authorities are set to vote next month on scrapping leap seconds, the periodic one-second adjustments used since 1972 to keep Coordinated Universal Time (UTC) aligned with the Earth's rotation. The move is driven by growing concern over the possibility of a "negative" leap second, something never attempted before, which could seriously disrupt computer systems, telecommunications, power grids and satellite navigation because most digital infrastructure assumes seconds are only ever added, never removed.
Under the draft resolution, UTC would become continuous from 20 May 2027, allowing it to drift from Earth-rotation-based time (UT1) by up to an hour, far beyond the current 0.9-second tolerance. The change follows a slight speeding up of Earth's rotation, which experts estimate gives a 30 percent chance of requiring a negative leap second by 2035. Setnam Shemar of the UK's National Physical Laboratory said the vote, expected in October at the General Conference on Weights and Measures, is likely to pass given broad international support, and would remove the need for further adjustments for at least a thousand years.
In short
- Global vote set for October on ending leap seconds by 2027
- Fear of a disruptive "negative" leap second drove the change
- UTC could then drift from Earth time by up to an hour
Steelman: both sides, in good faith
The strongest fair case each way — we don't pick a winner.
The case for
Ending leap seconds would make UTC more predictable for digital systems that depend on a uniform time scale, avoiding the risk of an unprecedented second being removed and disrupting infrastructure. Supporters can argue that allowing a larger gap from Earth-rotation time is a practical trade-off, especially if it prevents recurring technical risks for decades or centuries.
The case against
Keeping leap seconds would preserve UTC’s close link to Earth’s rotation, maintaining a common time standard that reflects the planet’s day rather than allowing the two to drift substantially apart. Critics can argue that a possible future software challenge should be addressed through better system design, rather than changing a long-standing convention in ways that may complicate timekeeping for navigation, astronomy and other users.
Explained simply
Global timekeeping has relied on "leap seconds" since 1972, extra seconds occasionally added to Coordinated Universal Time (UTC) to keep it in step with the Earth's actual rotation, which is not perfectly steady. Because computers, telecoms networks, power grids and satellite navigation systems are built around clocks, any change to how time is measured can ripple through infrastructure that people rely on every day.
The issue now is that Earth's rotation has been speeding up slightly, raising the prospect of a "negative" leap second, where a second would need to be removed rather than added. This has never happened before, and experts worry that many systems, designed only to cope with seconds being added, could malfunction if one had to be taken away instead.
International bodies responsible for setting global timekeeping standards, including scientists such as Setnam Shemar at the UK's National Physical Laboratory, are due to vote on a proposal to stop making these adjustments altogether. The decision, expected at a major standards conference next month, matters because it would change how precisely clocks track the Earth's rotation for centuries to come, affecting anyone who depends on precise timing technology.