On Thursday, the 69 member states of the International Bureau of Weights and Measures (BIPM) are scheduled to vote on a proposal that would remove the leap second from Coordinated Universal Time (UTC). The decision, if approved, would take effect in May 2027 and would fundamentally change the relationship between atomic time and Earth’s rotation.
Why the leap second matters
Since 1972, 27 leap seconds have been inserted into UTC to keep the atomic timescale aligned with astronomical time, which is based on the planet’s rotation. Earth’s spin is not constant; it wobbles because of lunar gravity, movements of water and ice, and shifts in the planet’s core. These irregularities have been described by Jeff Sherman of the National Institute of Standards and Technology as making Earth a “lousy” clock.
The occasional extra second is intended to keep UTC and the rotation‑based time used by observatories in sync. Most people never notice the adjustment, but the irregular timing—announced only six months in advance—has caused problems for data servers, high‑frequency trading platforms, and other systems that rely on precise timestamps. Notable incidents include outages at Reddit and LinkedIn in 2012, a disruption of Qantas’s booking system the same year, and brief service delays for Cloudflare after the 2016 leap second.
Technology firms such as Meta have labeled the leap second a “major source of pain,” prompting calls for its removal.
The proposed shift to a leap hour
Rather than continue adding or, potentially, subtracting seconds, the BIPM resolution would allow atomic time to drift away from Earth’s rotation. The proposal sets a maximum allowable difference of 3,600 seconds—one hour—between the two scales. According to BIPM’s time‑department director Patrizia Tavella, reaching that one‑hour gap would require more than 3,000 years.
Should the gap approach the limit, future generations would face the choice of inserting a “leap hour” to bring the two timescales back into alignment. Louise Devoy, senior curator at the Royal Observatory Greenwich, emphasizes that such a change would likely be invisible in daily life, noting that people’s routines remain tied to daylight regardless of the underlying clock.
The move is framed as a way to avoid the emerging prospect of a negative leap second. A 2025 report from the International Earth Rotation and Reference Systems Service estimated a 30 % chance of needing to subtract a second by 2035, a scenario for which critical‑infrastructure operators are largely unprepared. BIPM likened the required industry investment to the preparations made for the Y2K bug.
Opposition and alternatives
Not everyone agrees that abandoning the leap second is advisable. Marek Ziebart, a professor of space geodesy at University College London, argues that the existing system works and that removing the second would force widespread software redesign. He also stresses the “intrinsic relationship” humans have with Earth’s rotation, which gives a natural sense of time.
Historically, some member states have resisted the change. Russia opposed the 2022 proposal because its GLONASS navigation system incorporates leap seconds, unlike GPS and Galileo. The United Kingdom once objected on cultural grounds, given Greenwich’s historic role in global timekeeping, though its position has since softened.
At the Versailles meeting, a majority vote is required for the resolution to pass. If approved, the world would transition to what Tavella calls Continuous Coordinated Universal Time, effectively decoupling the global clock from the planet’s irregular spin for the foreseeable future.
The outcome will shape how scientists, engineers, and everyday users experience time in an increasingly digital world, potentially relegating the ancient link between the sun’s position and our clocks to a historical footnote.
Helene Elliott is the Lead Science & Space Reporter at News Raise. She reports on aerospace missions, astrophysics discoveries, quantum research, and environmental technology.
