Why the Leap Second Is Being Abandoned and What It Means for Tech Ops

At the recent International Bureau of Weights and Measures meeting, officials announced the formal decision to abolish leap seconds.

What Is a Leap Second?

Leap seconds were introduced because the atomic clock’s 86,400‑second day does not perfectly match Earth’s rotation, causing a cumulative error. Since 1972, an extra second has been added on either June 30 or December 31 to keep UTC aligned with solar time.

To date, 27 leap‑second adjustments have been made, all as positive additions, the most recent occurring at the turn of 2016‑2017.

Why Leap Seconds Trouble Tech Systems

The extra second can disrupt time‑sensitive software. In December 2016, Alibaba Cloud warned customers that leap‑second adjustments might affect applications and urged risk assessments.

Major companies such as Google, Meta, Microsoft and Amazon mitigate the issue by splitting the extra second into many tiny intervals, effectively “smoothing” the jump without breaking services. Some operators even pause NTP (Network Time Protocol) for one second to insert the missing time.

Despite these workarounds, incidents still occur. In 2012 Reddit suffered a half‑hour outage when a Linux system failed to handle the added second. Cloudflare’s DNS service crashed in the 2017 New Year when its software produced a negative timestamp. Other platforms—including Mozilla, LinkedIn, Yelp and Australian airlines—have reported similar problems.

The Decision to Cancel Leap Seconds

The new resolution plans to take effect in 2035 and remain in place until 2135, giving metrology experts a century to seek better solutions.

Not all nations agree; Russia, whose GLONASS satellite system would need redesign, prefers to postpone the change until 2040. The final agreement also requires endorsement from the International Telecommunication Union (ITU), with discussions expected to conclude by the end of 2023.

While the removal will eventually ease the burden on developers, the transition won’t happen until 2035, meaning programmers must continue to handle leap seconds for years to come.

Reference links:

https://www.nature.com/articles/d41586-022-03783-5

https://arstechnica.com/science/2022/11/network-crashing-leap-seconds-to-be-abandoned-by-2035-for-at-least-a-century/

https://mp.weixin.qq.com/s/T1LlPXKniH4AAv6dn6-AXQ