World Weighs Scrapping the Leap Second for a Rarer 'Leap Hour' Instead

The 28th General Conference on Weights and Measures (CGPM), meeting in Versailles this October, is expected to vote on the future of the leap second, the extra moment periodically added to keep clocks in step with Earth's rotation. Officials appear to favor letting Coordinated Universal Time (UTC) drift further from Earth's spin and adjusting it by a full hour when needed, rather than nickel-and-diming it with individual seconds each year.

The underlying problem is that Earth's rotation is not perfectly consistent: melting ice, shifting wind patterns and changing tidal forces redistribute the planet's angular momentum, and its spin can change speed by more than a second each year. Left unchecked, this drift could confuse global systems that coordinate actions with split-second precision using atomic clocks. The International Bureau of Weights and Measures introduced the leap second in 1972 to keep UTC in line with Earth's slightly longer days, and a total of 27 leap seconds have been added since then, the last in 2016.

In 2020, Earth's rotation began speeding up again, raising the possibility that a second might eventually need to be cut from the year instead of added, a negative leap second that has never been implemented and carries real risk since few modern computing systems were designed with this kind of time debt in mind. Leap seconds have previously caused problems for companies, including grounded flights and network glitches. Four years ago, CGPM members concluded that the frequent, tiny adjustments were more trouble than they were worth, and many tech companies, including Google, already smooth the discrepancy by stretching seconds slightly rather than inserting an abrupt leap second.

Under the proposal, officials would wait until UTC and Earth's spin disagree by as much as an hour before adjusting the official time, a leap hour that would only need to be added every few centuries. If enough CGPM members vote in favor of the draft proposal this October, the count toward that leap hour would begin from May 20 next year.