In a landmark decision, international scientists, diplomats, and timekeepers on Thursday (Oct 15) voted to end the leap second. Gathered at a conference of the International Bureau of Weights and Measures in France, the decision was reached after decades of discussion and debate. The leap second will now be replaced with a leap hour to keep clocks in sync across the world.
“After 30 years of debate, the leap second is making way for the leap hour,” said Dr Setnam Shemar, principal scientist in the time and frequency department at the UK’s National Physical Laboratory (NPL). “This will reduce the risks to the systems and national infrastructure that depend on accurate time while still preserving the fundamental link between our global time system and the rotation of the Earth.”
Since the dawn of history, Earth’s rotation on its axis has been the basis for timekeeping. However, since Earth does not rotate at a consistent speed due to several factors, including tides, melting ice and earthquakes, the astronomical time and time measured by highly precise atomic clocks can gradually drift apart.
To compensate for this inconsistency, timekeepers have been adding a leap second every few years since 1972. The last one was added in 2016 to keep clocks and Earth’s rotation in perfect harmony. While the leap second solution works to establish synchronisation, it has also led to challenges for technology companies, financial markets and other businesses that depend on precise timings.
In 2012, when a leap second was added, LinkedIn and Reddit experienced crashes, while ticket booking for Australian airline major, Qantas, collapsed. In July 2022, engineers at Meta issued a warning, stating that every leap second was a “major source of pain for people who manage hardware infrastructures.”
Problems associated with leap second have only compounded as Earth’s rotation has sped up in the past decade. As per scientists, this increase in rotation means that timekeepers would have been forced to add the first negative leap second.
Clocks work based on Coordinated Universal Time (UTC), the global standard that has been based on high-precision atomic clocks for more than seven decades. Every few years, a leap second is added to UTC to make it synchronise with the Earth’s rotation. A leap second is typically inserted in the last minute of either December or June, or, exceptionally, March or September, immediately prior to midnight or 00:00:00 hours UTC.
The decision as to whether a leap second is required is taken by the Earth Orientation Center of the International Earth Rotation and Reference Systems Service (IERS), approximately 6 months in advance. There have been 27 leap seconds added so far, with no plans to add another after the Paris outcome.
