The International Bureau of Weights and Measures is set to vote on scrapping the leap second, a timekeeping adjustment that could disrupt global systems, as experts warn of risks from a potential negative leap second by 2035.
The global timekeeping community faces a critical decision as the International Bureau of Weights and Measures (BIPM) prepares to vote on ending the leap second, a practice that has synchronized atomic clocks with Earth’s rotation since 1972.
The Leap Second’s Technical Risks
The leap second, added 27 times since the 1970s, has long been a source of tension for technology systems reliant on precise synchronization. Justin Greis, CEO of consulting firm Acceligence, argued that preserving the relationship between civil time and Earth’s rotation is outweighed by the operational risks to financial systems, telecommunications, and critical infrastructure. For the overwhelming majority of enterprise technology, I don’t think it is,
he said, highlighting the cascading effects of even minor time discrepancies across interconnected systems.
Experts like Kolev emphasized the complexity of managing leap seconds across distributed systems. “An enterprise does not only have to worry about what its own servers do. It has to consider what happens when its cloud provider, operating system, identity provider, database, external APIs, and on premises systems interpret the same moment differently,” he explained. This systemic risk, he added, is compounded by the lack of a unified approach to handling leap seconds, with some companies “smearing” the adjustment over a day while others add a full second to a specific minute.
A Negative Leap Second and Its Unprecedented Risks
Recent shifts in Earth’s rotation have intensified the debate. Since around 2015, the planet’s spin has accelerated, increasing the likelihood of a negative leap second by 2035—a scenario where clocks would need to “skip” a second rather than add it. This unprecedented move, never attempted before, has raised alarms among researchers. Georgette Macdonald, director-general of the Metrology Research Centre in Halifax, Canada, warned of equipment failures
and the unprecedented risk
of disrupting critical infrastructures like power grids and financial networks.
Aligning the timekeeping systems only after they have drifted apart by an hour has several advantages,
Macdonald said. It wouldn’t occur for hundreds, if not thousands, of years,
she added, noting that the leap hour would be more manageable than the current system, which already faces challenges in countries using daylight-saving time.
The Upcoming Vote and Global Implications
The decision rests with the General Conference on Weights and Measures (CGPM), which will convene outside Paris on 13–15 October to finalize the resolution. The vote comes amid growing pressure to modernize timekeeping practices, with some arguing that the leap second is an outdated relic of a pre-digital era. We end up with this discontinuity in a system that’s intended to be continuous,
Macdonald said, underscoring the need for a more resilient framework.
As the CGPM prepares to deliberate, the outcome will shape how global systems navigate the tension between precision and practicality in the decades ahead.
If approved, the shift would mark a significant departure from a practice that has defined timekeeping for over half a century. For now, the debate highlights the growing complexity of managing time in an era where even a single second can have far-reaching consequences.
