International bodies set to vote on ending leap seconds, allowing UTC to drift up to an hour

The General Conference on Weights and Measures is scheduled to vote in October on a draft resolution that would make Coordinated Universal Time (UTC) continuous from May 20, 2027, and allow its difference from UT1, the time based on Earth’s rotation, to grow to as much as one hour. Since 1972, 27 leap seconds have been added to keep UTC within 0.9 seconds of UT1. Recent measurements suggest a slight increase in Earth’s rotational speed, raising the probability of a negative leap second—removing a second rather than adding one—to about 30 percent by 2035.

"Most digital architectures and network time servers are hard-coded under the assumption that leap seconds are strictly additive. Losing a second could trigger severe disruption across critical national infrastructure, including telecommunications, electricity grids, and satellite navigation systems," said Setnam Shemar, principal scientist at the UK’s National Physical Laboratory. The proposal aims to eliminate the need for future leap-second adjustments, which have been viewed as a risk to national infrastructure. Shemar added that the change would likely prevent any further leap-second events for many years and that a full hour of divergence from rotational time would not be expected for at least a millennium.