Karachi | ReNews Pakistan

A major change in the global system of timekeeping has been approved following decades of efforts to reconcile highly accurate atomic clocks with the irregular rotation of the Earth. At an international conference in Versailles, France, delegates agreed to abolish the leap second system, which has been used since 1972 to keep the world's clocks aligned with the planet's rotation.

The decision will end the practice of occasionally adding or removing a second from Coordinated Universal Time (UTC), allowing small differences between atomic time and time measured through Earth's rotation to accumulate over longer periods.

The resolution was adopted on October 15, 2026, during the 28th meeting of the General Conference on Weights and Measures (CGPM), organised under the International Bureau of Weights and Measures (BIPM). The conference was held from October 13 to 15 in Versailles.

Under the approved resolution, continuous UTC will take effect on May 20, 2027, eliminating the need for leap second adjustments that have historically been introduced to maintain close alignment between atomic clocks and the Earth's rotation.

The leap second was introduced in 1972 because Earth does not rotate around its axis at a perfectly uniform speed. Although a day is conventionally measured as 24 hours, or 86,400 seconds, the actual duration of Earth's rotation varies slightly due to natural physical processes.

These variations create a difference between astronomical time, which is based on the Earth's rotation, and atomic time, which is maintained using extremely precise atomic clocks.

Scientists explain that the Earth's rotation has gradually slowed over geological timescales, largely because of tidal friction associated with the gravitational influence of the Moon.

However, the planet's rotation also experiences shorter-term fluctuations, occasionally accelerating or slowing down because of movements within the Earth's interior, changes in atmospheric circulation, ocean currents and variations in the distribution of water and ice across the planet.

In recent years, scientists have observed periods during which Earth has rotated slightly faster than expected, resulting in some days being shorter by a few milliseconds.

This unexpected acceleration raised the possibility that timekeepers might eventually need to introduce a negative leap second, removing one second from global clocks rather than adding an extra second.

Such an adjustment has never been implemented, creating concerns about how computers, telecommunications networks and other critical digital systems would respond.

According to the BIPM, a workshop involving experts in Earth rotation and timekeeping in March 2025 estimated that the probability of requiring a negative leap second could reach approximately 30% by 2035.

The possible introduction of a negative leap second was considered particularly challenging because many essential technological systems have not been designed or tested to accommodate such a change.

Under the previous system, a leap second could be introduced when the difference between Coordinated Universal Time and astronomical time, known as UT1, was expected to approach 0.9 seconds.

When necessary, an additional second was inserted into the global timekeeping system to prevent the two measurements from drifting too far apart.

Since the introduction of leap seconds in 1972, a total of 27 additional seconds have been inserted into UTC. The last adjustment occurred on December 31, 2016.

No further leap second was introduced during the following years, reflecting changes in the observed relationship between atomic time and Earth's rotation.

Atomic clocks measure time using highly stable atomic frequencies, providing substantially greater precision than timekeeping based on the Earth's natural rotation.

While atomic clocks operate at a consistent rate, Earth's rotation is influenced by multiple physical processes and therefore cannot serve as an equally uniform reference.

The difference between these two methods of measuring time was the principal reason for introducing leap seconds more than five decades ago.

However, modern infrastructure increasingly depends on precise and uninterrupted time synchronization.

Global financial transactions, telecommunications, electricity distribution, aviation, satellite navigation, internet services and advanced computing networks all rely on highly accurate time references.

Experts have warned that inserting or removing a second can create inconsistencies in computer systems, particularly when different operators use incompatible methods to accommodate the adjustment.

Previous leap-second events have been associated with technical disruptions affecting some online services and digital platforms.

The new resolution seeks to address these concerns by making Coordinated Universal Time a continuous time scale without abrupt leap-second adjustments.

Under the decision, the maximum permitted difference between UTC and UT1 will increase to 3,600 seconds, equivalent to one hour.

This does not mean that one hour will immediately be added to or removed from the world's clocks. Instead, the small difference between atomic time and Earth's rotation based time will be allowed to accumulate gradually.

Scientists expect that reaching such a large discrepancy could take several centuries, meaning the change is not expected to affect ordinary daily schedules, business hours, school timetables or public transport operations in the immediate future.

The international community had already agreed in November 2022 that the existing leap-second system should be modified by or before 2035.

However, the October 2026 conference brought forward implementation, approving the transition to continuous UTC from May 20, 2027.