The International Bureau of Weights and Measures (BIPM) has voted in favor of the complete abolition of leap seconds — a mechanism that for decades has kept reference atomic time synchronized with the Earth's real, irregular rotation. The decision to abolish them will take effect on May 20, 2027, World Metrology Day. This is significantly earlier than the timeline set in 2022, when BIPM participants agreed to phase out leap seconds "by 2035 or earlier." According to the bureau, this acceleration is driven not by administrative reasons, but by technical factors related to the changing nature of the planet's rotation.
What Is a Leap Second and Why It Existed
Atomic clocks, which form the foundation of modern timekeeping, tick with extreme precision. However, the Earth's rotation around its axis is not strictly uniform: it constantly slows down and speeds up due to tidal forces, mass redistribution, and other factors. To prevent atomic time from falling behind astronomical time, an extra leap second has been periodically added since 1972, usually at the end of June or December. Throughout the history of this mechanism, 27 such seconds have been added, and none have ever been subtracted.
Why the Decision Was Made Ahead of Schedule
The key reason for accelerating the phase-out is an unprecedented scenario: changes in the Earth's rotation patterns mean that in the near future, it may become necessary not to add, but to subtract seconds to maintain synchronization between atomic and astronomical time. Such an operation has never been performed in the history of metrology, and BIPM experts fear that a "negative leap second" could trigger severe disruptions in critical infrastructure dependent on precise timing synchronization — from financial systems and telecommunications to power grids and navigation.
Failures Have Already Happened: Real-World Experience
The bureau's fears are not purely theoretical. Even standard, "positive" leap seconds have previously caused outages on major internet platforms: disruptions were reported on Foursquare, Reddit, LinkedIn, Yelp, and several other services whose systems were not prepared for days being one second longer. This exact experience became one of the main arguments for abandoning a fragile mechanism that embeds a potential single point of failure into global infrastructure.
What Will Replace Leap Seconds
The decision to abolish them has been supported by major technology companies whose systems are most sensitive to time anomalies, including Meta, Google, Microsoft, and Amazon. Instead of periodic second adjustments, it has been proposed to transition to so-called leap hours: atomic and astronomical time will gradually drift apart until the accumulated difference reaches a full hour. According to specialists' forecasts, this will not happen for at least three thousand years, effectively removing the risk of frequent synchronization interventions from global infrastructure.
Timelines and Significance of the Decision
Formally, the BIPM decision takes effect on May 20, 2027, but practical implementation will require approval from the International Earth Rotation and Reference Systems Service (IERS), which directly announces the introduction of leap seconds, as well as software and standards updates by critical infrastructure operators. Essentially, the abolition of leap seconds represents a transition from a reactive model — where the time system is adjusted retroactively — to a predictable and stable one, reducing systemic risks for the digital services upon which a significant part of the global economy currently relies.
