The General Conference on Weights and Measures meets next month to vote on a draft resolution that would end the practice of adding leap seconds to Coordinated Universal Time (UTC). If adopted, UTC would become continuous starting May 20, 2027, and would be allowed to drift from UT1, the time scale based on Earth's rotation, by as much as one hour.

Leap seconds have kept UTC within 0.9 seconds of UT1 since the system began in 1972. Since then, 27 leap seconds have been inserted. The push to scrap them now comes from a recent speed-up in Earth's rotation, which raises the odds of something that has never happened before: a negative leap second, where a second gets removed rather than added. Experts convened by international timekeeping bodies put the chance of needing one by 2035 at 30 percent.

Setnam Shemar, principal scientist at the UK's National Physical Laboratory, warned that most digital systems and network time servers assume leap seconds only ever get added. A negative one could disrupt telecommunications, power grids and satellite navigation, he said. Letting UTC and UT1 diverge by up to an hour would remove that risk for a long stretch of time.

Shemar expects the October vote to pass, since it needs only a majority of national delegates, most of whom have wanted to end leap seconds for years given the infrastructure risks. He estimates UTC would not drift a full hour from rotational time for at least a thousand years, which should give everyone plenty of time to sort out the alarm clocks.