On Thursday, the International Bureau of Weights and Measures (BIPM) will hold a decisive vote in Versailles, France, on a proposal to eliminate the leap second. The leap second, added 27 times since 1972, has long served as a compromise between astronomical time—based on Earth’s rotation—and Coordinated Universal Time (UTC), which is kept by ultra‑precise atomic clocks.
Why the leap second matters
Earth’s spin is not constant; it wobbles due to the moon’s gravitational pull, shifts in the planet’s core, and the movement of water and ice. These variations have become more pronounced as polar ice caps melt, a consequence of the climate crisis. Jeff Sherman, group leader of the National Institute of Standards and Technology’s Time and Frequency Division, described Earth’s rotation as a “lousy clock,” underscoring the challenge of keeping time standards in sync.
When a leap second is inserted, it can cause brief disruptions for data servers, high‑frequency trading platforms, and other critical infrastructure that rely on precise timestamps. Past incidents include outages at Reddit, LinkedIn, and Qantas in 2012, as well as temporary delays for Cloudflare customers after the 2016 leap second.
The proposal and its supporters
Patrizia Tavella, director of BIPM’s time department, explained that the proposed resolution would replace the leap second with a system called Continuous Coordinated Universal Time. This would allow atomic time to drift gradually away from Earth’s rotation, eliminating the need for future adjustments. The change is slated to take effect in May 2027 if a majority of the 69 member states vote in favor.
Supporters argue that modern applications—such as GPS, telecommunications, and financial markets—benefit from a stable, laboratory‑based time standard. Tavella noted that the original need to tie atomic time to astronomical time has faded with the advent of satellite navigation systems that do not rely on leap seconds.
Opposition and concerns
Not everyone agrees that the leap second should be discarded. Marek Ziebart, a professor of space geodesy at University College London, cautioned that removing the leap second would require extensive software updates and could introduce new risks. He emphasized the “intrinsic relationship” humans have with Earth’s rotation, describing it as “intellectually comforting” to keep time linked to the planet’s spin.
Some countries, including Russia and the United Kingdom, have historically opposed eliminating the leap second. Russia’s GLONASS navigation system incorporates leap seconds, while the United Kingdom’s cultural attachment to Greenwich’s historic role has also been a factor. Both nations have softened their positions in recent years.
Future challenges
Scientists warn that Earth’s rotation may soon require a “negative leap second,” where a second would be subtracted rather than added. A 2025 report from the International Earth Rotation and Reference Systems Service estimated a 30% chance of a negative leap second by 2035. BIPM acknowledges that operators of critical infrastructure are largely unprepared for such a scenario, likening the required investment to the preparations made for the Y2K computer bug.
Instead of tackling the technical complexities of positive or negative leap seconds, the BIPM proposal essentially punts the problem to future generations, who may need to consider a “leap hour” adjustment if the drift becomes significant.
What’s at stake
The outcome of the Versailles vote will shape how the world measures time for decades to come. Eliminating the leap second could simplify timekeeping for modern digital systems, but it also raises philosophical questions about humanity’s connection to the natural rhythms of the sun and the planet.
Original reporting: 40/29 / KHBS (NW Arkansas) — read the source article.
