Timekeepers bring forward end of leap seconds to next May
The International Bureau of Weights and Measures has voted to bring forward the end of leap seconds, with the change due to take effect on 20 May next year. Leap seconds have occasionally been added to make atomic time track the Earth’s irregular rotation; ending them is intended to reduce the risk of failures in systems that depend on precise timekeeping.
The change was previously planned for 2035, but shifts in Earth’s rotation could soon require a leap second to be subtracted for the first time, raising concerns about the effect on critical infrastructure. Past leap-second additions have coincided with outages at platforms including Reddit and LinkedIn, and major technology companies have backed scrapping the system. Timekeepers will instead let atomic and astronomical time gradually diverge, using a “leap hour” only after roughly 3,000 years.
- Leap seconds are due to end on 20 May next year.
- The change aims to reduce risks to time-dependent infrastructure.
- A leap hour is not expected for around 3,000 years.
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Atomic clocks keep Coordinated Universal Time, the standard used to set clocks around the world. Because Earth’s rotation varies slightly, this atomic time can drift from time based on the Sun’s position; leap seconds have occasionally been added to keep the two close.
The International Bureau of Weights and Measures oversees international standards for measurement, including time. Computers, communications networks and other systems rely on precise time, and adjusting clocks by a second can cause technical problems. Under the new approach, atomic time will be allowed to drift gradually from time based on Earth’s rotation, with a larger adjustment envisaged far in the future.
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The case for
Ending leap seconds sooner could reduce the risk of outages in computer networks and other systems that rely on precise, consistent timestamps. A negative leap second would be unprecedented, so moving to the new approach now gives operators time to adapt and avoids an increasingly fragile adjustment that major technology companies say can disrupt services.
The case against
Leap seconds preserve the link between atomic time and the Earth’s rotation, which supports navigation, astronomy and other activities that use astronomical time. Letting the two measures drift apart for centuries may shift the burden to future generations, while the reported outages could be addressed through better system design rather than abandoning the adjustment.
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Originally published by The Verge as “Time is a-changin’: say goodbye to the leap second”.