World's Clocks to Drift from Earth's Rotation as Leap Seconds Are Scrapped

In a significant shift for global timekeeping, scientists have voted to discontinue the use of leap seconds, effectively severing the long-standing connection between modern clocks and the Earth's rotation. The decision, made by a majority vote at the International Bureau of Weights and Measures (BIPM) meeting in Versailles, France, will allow Coordinated Universal Time (UTC) to drift by up to one hour, or 3,600 seconds, from astronomical time (UT1).

This change, scheduled to take effect on May 20, 2027, World Metrology Day, means that time adjustments may not be necessary for centuries. Leap seconds, first introduced in 1972, have been added 27 times to UTC to keep atomic clocks synchronized with the Earth's slightly variable spin. However, these adjustments have become increasingly problematic for digital infrastructure.

"Leap seconds have given way to the leap hour to reduce the risks to systems that depend on accurate time," said Dr. Setnam Shemar, principal scientist at the National Physical Laboratory. "Humanity will still retain the important link between its global time system and the Earth’s rotation, although more loosely."

While the Earth's rotation slows and speeds due to factors like lunar gravity and the melting of polar ice caps, atomic clocks, which measure time by atomic vibrations, are far more precise and consistent. This discrepancy has created challenges for high-precision computing systems.

Data centers, financial trading platforms, and other systems relying on precise time synchronization have experienced disruptions when leap seconds were implemented. For instance, the addition of a leap second in 2012 caused outages for websites like Reddit and LinkedIn, and delayed flights for Qantas. In 2016, similar issues affected Cloudflare customers. Meta has also been a vocal proponent of eliminating leap seconds, citing them as a major source of pain for infrastructure management.

Engineers had grown increasingly concerned about the potential for a "negative leap second"—removing a second from UTC—as early as 2029, due to the Earth's rotation unexpectedly speeding up in the mid-2010s. Such an adjustment could have caused a "mini Y2K" event, disrupting computer systems unprepared for a backward time shift. The new system avoids this immediate risk by allowing a much larger divergence between UTC and UT1.

Under the revised system, BIPM would only intervene if the time difference reached a full hour, an event not anticipated for at least another 1,000 years. This will alleviate uncertainty for those maintaining time-dependent infrastructure, ensuring greater stability for critical digital systems worldwide.