Since 1972, a total of 27 leap seconds have been incorporated into global timekeeping. This adjustment is necessary because atomic clocks maintain incredibly precise time, while the Earth's rotation can fluctuate slightly in speed. The most recent leap second was added in 2016. However, these adjustments can create challenges for computer systems, as there is no universal approach to managing them. Georgette Macdonald, the director-general of the Metrology Research Centre in Halifax, explains that this leads to a disruption in a system that is designed to be seamless.
Typically, a leap second causes the clock to transition from 23:59:59 to 23:59:60 before midnight. Google addresses this issue by distributing the extra second over a full day, while some stock markets modify their trading hours to avoid dealing with a 61-second minute.
Why is the leap second being reconsidered now? In recent years, particularly since around 2015, the Earth has been rotating at a quicker pace. This increase may be partially attributed to changes in the flow of the planet's liquid outer core. If this trend persists, the world might face an unprecedented situation: the need to subtract a second instead of adding one. There is an estimated 30% likelihood that a negative leap second could be required by 2035, but crucial infrastructure is largely unprepared for such a scenario. The International Bureau of Weights and Measures has indicated that preparing for this possibility could involve investments comparable to those needed for the Y2K crisis.
To mitigate this potential risk, authorities are contemplating making Coordinated Universal Time (UTC) a continuous measure starting May 20, 2027. This change would allow UTC to drift further away from the Earth's rotation, potentially by as much as one hour. Achieving such a divergence could span hundreds or even thousands of years, leaving future generations to make the next adjustment. This pivotal decision is set to be discussed in October during the General Conference on Weights and Measures in Versailles.
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