A vote on Thursday in Versailles

The International Bureau of Weights and Measures, which safeguards SI units such as the second, the metre and the kilogram, will vote on Thursday, 15 October, on whether to abolish the leap second. The ballot is part of the 28th General Conference on Weights and Measures (CGPM) in Versailles, southwest of Paris. About seventy countries hold voting rights, and De Standaard expects a large majority to vote in favour. Le Monde places the vote in the afternoon, while eldiario.es gives midday as the time.

Why the leap second exists

Timekeeping was tied to the rotation of the Earth for centuries, but that rotation is not constant. The pull of the Moon and Sun, processes inside the planet and shifts in water and ice all alter its speed, whereas atomic clocks keep very steady time. To stop the two drifting apart, Coordinated Universal Time (UTC) was allowed to differ from astronomical time by no more than 0.9 seconds. When that limit is reached, an extra second is inserted. This has happened 27 times since 1972, most recently at the end of 2016.

Why the rule may flip

Earth has spun faster in recent years, which could make a negative leap second necessary for the first time, meaning one second would be removed instead of added. METAS, the Swiss federal metrology institute that takes part in the work, describes the scenario as an entirely new situation. Most systems were designed and tested only for an added second, so their reactions to a removed one are potentially unpredictable, according to the institute. Telecommunications, computer networks, financial market infrastructure and industrial plants that rely on precise time synchronisation could all be affected.

Positions and the 2035 deadline

An earlier CGPM meeting had already decided to end the leap second in 2035, but this proposal would bring that change forward to avoid the first negative adjustment. Russia is the only member that wants to keep the leap second, De Standaard reports, because its GLONASS navigation system is set to it. Belgium is expected to back the change as well. Pascale Defraigne, who represents the time department of the Royal Observatory of Belgium, said:

The leap second only leads to problems, mainly in systems that depend on precise time measurement.

Organisations also handle the extra second differently. Google, for example, spreads it gradually over the course of the day, and GLONASS incorporates UTC into its operation.

What comes next

Swissinfo describes Thursday's session in Versailles as the final confirmation of the change. The BBC reports that experts are deciding whether to scrap leap seconds altogether and replace them with a 'leap hour' instead, and that the decision is due this week. If the resolution passes, the change would be settled at the conference itself, ending a correction system that has operated since 1972.