Historic Decision Reached to Abolish the Leap Second Starting in 2027

The General Conference on Weights and Measures (CGPM), meeting in Versailles near Paris, has officially decided to abolish the leap second starting May 20, 2027. The historic move will establish a continuous Coordinated Universal Time (UTC) designed to bring greater stability to global timekeeping and protect modern technical infrastructure.

Time measurement currently relies on two different foundations: UTC, which is based on the unyielding constancy of atomic clocks, and astronomical time (UT1), which is determined by the rotation of the Earth. Because our planet's rotational speed fluctuates irregularly due to tidal forces from the moon and sun, core movements within the Earth, and climate changes, the two time scales gradually drift apart.

Previously, to keep the two systems aligned, a leap second was inserted whenever the discrepancy reached 0.9 seconds. Since the procedure was introduced in 1972, exactly 27 leap seconds have been added by the International Earth Rotation and Reference Systems Service, with the most recent adjustment occurring at the end of 2016. These additions turned a normal minute into one lasting 61 seconds.

However, sudden inserted or omitted seconds have increasingly created severe problems for modern computer systems, server networks, navigation systems, and critical infrastructure such as telecommunications, energy supplies, and transportation. A sudden temporal jump can easily disrupt complex technical processes and data flows.

The decision to phase out the system sooner than originally planned was heavily influenced by recent shifts in the Earth's rotation. While Earth's rotation is slowed over long periods by lunar and solar gravitational forces, experts noted that the planet has actually accelerated slightly in recent years. This raised the unprecedented prospect of needing to subtract a negative leap second rather than add one.

A negative leap second would have forced systems to drop a second, a scenario never before attempted and one that industry leaders feared would cause widespread technical failures and significant additional costs. Under the new framework approved by the CGPM, the permitted deviation between atomic time and Earth rotation will expand significantly, allowing up to 3,600 seconds—a full hour—of divergence before any adjustments are required.

Experts predict that this major tolerance increase will ensure timekeeping remains unadjusted for several centuries. While the change will cause UTC and astronomical time to slowly drift further apart, the impact on everyday human life will be practically nonexistent. The shift will primarily affect specialists who work directly with astronomical time, such as astronomers and geodesists.