Leap Second on the Brink: Global Timekeepers Debate Scrapping Earth's Rotation Sync

(Al Jazeera) Global timekeepers convened near Paris on Thursday to deliberate the potential elimination of the "leap second," a move that could decouple our everyday clocks from the Earth's rotational speed and harmonize timescales. The world's timekeeping systems are fundamentally based on the premise that the Earth completes a rotation on its axis in precisely 24 hours. However, the Earth's rotation is not perfectly consistent; it experiences wobbles, leading to variations in the time it takes for a full rotation. Furthermore, the Earth's rotation is gradually decelerating over time. To address this discrepancy, timekeepers have been adding a leap second periodically since 1972 – the most recent addition occurred in 2016 – to maintain synchronization between clocks and the Earth's rotation. Nevertheless, significant pressure has mounted to abolish the leap second due to the complications it introduces for financial markets and data centers, which depend on millisecond-level precision. This article explores the nature of the leap second, the arguments for its removal, and the potential implications for our understanding of time.

What is a Leap Second?

Clocks operate based on Coordinated Universal Time (UTC), the international standard that has relied on high-precision atomic clocks for over seven decades. Atomic clocks measure time by observing the vibrations of atoms. In contrast, the Earth's rotation operates independently of atomic clocks. A leap second is an extra second occasionally inserted into UTC to align it with the Earth's rotation. The first leap second was introduced to global clocks in 1972, and a total of 27 have been added since, with the last one on December 31, 2016. No leap seconds have been added since then. According to the National Institute of Standards and Technology (NIST), a U.S. Department of Commerce agency, leap seconds are typically added at the end of June or December. NIST attributes the necessity of leap seconds to the precision differences between the atomic second and the Earth's rotation. The institute notes, "The speed of the Earth’s rotation is not constant. …. This gradual decrease in the rotational rate is causing the duration of the mean solar second to gradually increase with respect to the atomic second."

Why is Pressure Mounting to Scrap Leap Seconds?

While leap seconds serve to bridge the gap between the Earth's rotation and UTC, their implementation has presented challenges for technology companies, financial markets, and other businesses reliant on precise timing. In 2012, major platforms like LinkedIn and Reddit experienced outages following the addition of a leap second. Similarly, Qantas, the Australian airline, suffered booking system failures in the same year. Three years later, the Australian Securities and Investments Commission issued a cautionary statement regarding leap seconds. In July 2022, Meta engineers described leap seconds as "a major source of pain for people who manage hardware infrastructures." In response to this mounting pressure, the International Bureau of Weights and Measures (BIPM), identified by its French acronym, voted in 2022 to eliminate the leap second by 2035. However, nations such as Russia have advocated for a later implementation date of 2040, as Russia integrates leap seconds directly into its GLONASS satellite-navigation system and would require time to update its infrastructure. Despite these concerns, the 69 member states of the BIPM are currently meeting in Versailles, France, to debate and vote on a resolution to abolish the leap second by 2027.

What's Under Discussion on Thursday?

The BIPM has outlined three key proposals to be discussed by global timekeeping authorities in Versailles. Firstly, the delegates will consider whether atomic clocks remain the most accurate instruments for measuring a second, given that optical frequencies now offer superior precision. A decision to adopt a new definition of the second, based on optical frequencies rather than atomic vibrations, could be made. The most significant proposal, however, concerns the discontinuation of the leap second. Finally, a third proposal involves synchronizing Earth-based time measurements with a new time standard being developed by NASA for lunar applications. Any adopted proposals are anticipated to take effect from May 20, 2027, designated as World Metrology Day.

What Happens if the Leap Second is Scrapped?

The elimination of the leap second would signify that our clocks would no longer be synchronized with the Earth's rotation. The NIST explains that if this occurs, "adjustments would have to be made to time stamps and legacy equipment and software which synchronise to UTC for astronomical observations." The NIST also mentioned that "Some proposals have been made to implement larger corrections like leap hours, which would occur much less often than leap seconds." Scientists anticipate that human daily routines would remain unaffected, and the abandonment of leap seconds would prevent software glitches, data server crashes, and network failures in financial markets. However, over centuries, the divergence between the Earth's natural cycles and our clocks would become increasingly noticeable. By the year 2100, clocks are projected to be 54 seconds ahead of the Earth's rotation. In approximately two millennia, this discrepancy could widen to several hours, potentially leading to a noticeable misalignment between the times of sunrise and sunset and people's natural circadian rhythms.