Time is a-changin’: say goodbye to the leap second

For decades, the world's timekeepers have quietly nudged our clocks by a single second every few years, and now that practice is heading for retirement. The decision to abandon the leap second, reported by The Verge under the headline "Time is a-changin': say goodbye to the leap second," marks one of the more unusual shifts in how humanity measures its days.

The change may sound trivial at first. After all, a single second hardly seems worth a global agreement. Yet behind that tiny unit lies a tangled story involving astronomy, atomic physics, computer engineering, and international diplomacy.

Below, we walk through what the leap second is, why it caused so much trouble, and what its disappearance means for the rest of us.

What Exactly Is a Leap Second Anyway

A leap second is a one-second adjustment added to Coordinated Universal Time, or UTC, to keep it close to the time based on Earth's rotation. Without it, our clocks would slowly drift out of step with the position of the sun in the sky.

The reason is simple: Earth does not spin at a perfectly steady rate. Tidal friction from the moon and other forces gradually slow the planet's rotation, which means a solar day is slightly longer than the 86,400 seconds defined by atomic clocks.

To reconcile the two, timekeepers occasionally insert an extra second, usually on June 30 or December 31. Since the system began in 1972, 27 leap seconds have been added.

How the Leap Second System Began

Before atomic clocks, time was defined by astronomy. A second was a fraction of a day, and the planet itself was the reference clock. That arrangement worked well enough for navigation and daily life.

The arrival of cesium atomic clocks changed everything, because they were far more stable than the spinning Earth. In 1972, international authorities introduced UTC and the leap second as a compromise between atomic precision and astronomical reality.

For a while the compromise seemed sensible. Few people noticed the extra second, and those who needed to account for it, such as observatories, generally managed.

Why Engineers Grew Tired of the Extra Second

As computer networks grew, the leap second became a headache. Software generally assumes that every minute has exactly 60 seconds, so a minute with 61 seconds can confuse systems in unpredictable ways.

Several high-profile outages have been blamed on leap second handling, affecting websites, databases, and airline systems. Engineers at large technology companies even developed workarounds, such as "smearing" the extra second across many hours instead of adding it all at once.

Those fixes worked, but they were inconsistent between providers. The lack of a common approach made the leap second a recurring risk rather than a solved problem.

The Global Vote to Abolish Leap Seconds

The turning point came when representatives from member countries at the General Conference on Weights and Measures agreed to phase out the leap second. The resolution calls for the practice to end by 2035.

After that date, the gap between UTC and Earth-based time will be allowed to grow much larger than it is today. The exact limit has yet to be set, but the goal is to avoid any adjustment for at least a century.

The decision reflects a growing consensus that the needs of modern technology outweigh the desire to keep clocks aligned with the sun to the second.

What Happens to Time After 2035

Once leap seconds stop, UTC will drift away from solar time very slowly. Over many decades, the difference could build up to a minute or more.

Eventually, timekeepers may need a new method of correction, possibly adding a larger adjustment such as a leap minute. That would be so far in the future that it is largely a problem for later generations.

For now, the plan gives engineers a stable, continuous timescale, which is exactly what satellite systems and financial networks prefer.

Why Scientists and Tech Companies Welcome the Change

Many in the technology industry have lobbied for this outcome. Companies such as Meta and Google argued that leap seconds create risks that outweigh their benefits, especially in data centers where precise timing is essential.

Metrologists have also supported the shift, noting that a uniform time scale is easier to maintain and distribute. Stable timing is vital for GPS, telecommunications, power grids, and high-frequency trading.

Not everyone was entirely happy, however. Astronomers who depend on Earth's rotation for tracking objects will need to rely on separate correction tables.

The Surprising Role of Earth's Changing Spin

Interestingly, Earth's rotation has recently sped up slightly, and in some years the planet has completed days a little shorter than average. This has raised the possibility of a negative leap second, where a second would be removed rather than added.

A negative leap second has never been tried, and many engineers fear it would cause even greater disruption than the positive kind. That uncertainty strengthened the argument for dropping the practice altogether.

Scientists continue to study the causes of these variations, which include changes in the planet's core, melting ice, and shifts in ocean and atmospheric patterns.

What the End of the Leap Second Means for You

For most people, the answer is almost nothing. Your phone, computer, and watch will keep showing the time just as they do today, and no one will feel the difference in daily life.

The benefits will be mostly invisible, appearing as fewer glitches and more reliable systems behind the scenes. That is often how the best infrastructure improvements work.

Still, it is a small reminder that even something as basic as a second is a human agreement, and one that can be revised as our needs change. The leap second had a good run, but time, as the headline says, is a-changin'.

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