Time Just Changed Forever: Scientists Kill the Leap Second and Approve a Leap Hour

Stop checking your watch — it’s about to tell time differently. Yesterday, the world’s official timekeepers voted to kill the leap second, a tiny correction that has quietly kept your clocks, phones, and the entire internet in sync with the spinning Earth since 1972. In its place, they approved something humanity may never live to see: the leap hour.

It was the final act of a debate that dragged on for three decades. Delegates from 69 countries gathered at the General Conference on Weights and Measures (CGPM) in Versailles, France, for the October 13–15 session, and on the last day they passed the resolution almost as an anticlimax. As Noël Dimarcq, president of the Consultative Committee for Time and Frequency, told the room before the vote: after 30 years of debate, the timekeepers were finally ready.

What Exactly Is a Leap Second?

Here’s the problem. Your clock ticks on atomic time — measured by cesium-133 atoms oscillating 9,192,631,770 times per second, a standard set back in 1967. That beat is perfectly steady. But the Earth is a terrible clock.

Our planet’s rotation wobbles and gradually slows, and it does so erratically — earthquakes, tides, melting glaciers, and churning molten core all nudge it. So astronomers track a second time scale called UT1, which follows the actual position of the Sun in the sky. The two scales drift apart, and since 1972 timekeepers have added 27 leap seconds to Coordinated Universal Time (UTC) to keep the difference under 0.9 seconds. The most recent one landed at the end of December 31, 2016.

Why the World’s Timekeepers Pulled the Plug

You’d think adding one second every few years would be trivial. It isn’t — at least not for the machines running modern life. When a minute lasts 61 seconds instead of 60, software chokes. A leap second in 2012 crashed chunks of Reddit, LinkedIn, and Yelp. In 2015, a leap second knocked Qantas’s systems offline and delayed flights. A 2017 leap second rattled Cloudflare’s infrastructure.

The real nightmare, though, was one nobody had ever handled: a negative leap second. Earth’s rotation has actually been speeding up in recent years, and experts estimated a 30% chance that by 2035 the planet would be so far ahead of atomic time that a second would have to be removed from the clock. As The Register reported, there is no large-scale precedent for that — and plenty of systems built only to add seconds, never to lose one.

Setnam Shemar, principal scientist at the UK’s National Physical Laboratory, put the stakes bluntly: implemented badly, leap seconds could take down mobile networks or electricity grids, and a first-ever negative leap second would multiply the risk. The same fragile tech stack that powers the world’s chip-hungry data centers and the AI boom runs on time precision — and nobody wanted to gamble it on a 59-second minute.

The Leap Hour: How the New System Works

The resolution is elegant in its audacity: instead of holding UTC within 0.9 seconds of astronomical time, allow it to drift by up to 3,600 seconds — a full hour. UTC becomes a continuous, unbroken time scale starting May 20, 2027, which is World Metrology Day.

When the gap eventually approaches an hour, timekeepers will insert a single leap hour to realign the scales. The catch? At the current rate of drift, that correction won’t be needed for centuries — possibly millennia. As Christian Bizouard of France’s Earth Orientation Center noted, it’s “kind of a philosophical discussion,” because pushing the fix that far into the future is essentially pushing back the decision. One scientist at the UK’s NPL compared it to daylight saving: we already shift our clocks by an hour twice a year and barely notice.

What Happens to Sunrise? And What’s Next?

If UTC drifts from the Sun, won’t noon eventually stop being noon? Technically, yes — but so slowly that no human alive will notice. The resolution keeps the fundamental link between civil time and Earth’s rotation intact while freeing every computer, satellite, and power grid from the periodic jolts. The International Bureau of Weights and Measures (BIPM) has been tasked with managing the transition alongside national time laboratories through 2027.

For most of us, nothing changes on the surface. Your phone will still say 8:00 when you wake up. GPS — whose satellites depend on nanosecond-level timing — will simply get more reliable. The experiments riding to the International Space Station, the stock exchanges timestamping billions of trades, the phone network stitching your calls together: all of them stop dodging a one-second landmine every few years.

Frequently Asked Questions

When does the leap second officially end?

The CGPM resolution takes effect on May 20, 2027. After that date, no new leap seconds will be added to UTC, and the time scale becomes continuous.

What is the leap hour, exactly?

A future one-hour correction that will realign UTC with Earth’s rotation if the two ever drift a full hour apart. Scientists estimate that won’t happen for centuries or even thousands of years — it’s a safety valve, not a scheduled event.

Will this affect my phone, computer, or GPS?

Only in a good way. Removing irregular one-second jumps makes timekeeping simpler and more reliable for the software running your devices, your mobile network, and GPS satellites. You won’t see any visible change.

Has a negative leap second ever happened?

No. Only positive leap seconds (extra seconds) have ever been added — 27 of them since 1972. The new resolution was partly driven by the looming risk of the first-ever negative leap second, which computer systems had no experience handling.

The Bottom Line

For half a century, humanity measured its days against an increasingly imperfect planet and patched the difference with stolen seconds — until the patches themselves became the danger. The leap hour is the world’s timekeepers admitting that perfection isn’t the goal anymore: resilience is. Your grandchildren’s grandchildren may one day live through the first leap hour. You’ll never even notice the one that disappeared.