It’s Time to Ditch the Leap Second: The Devastating Effect of Adding Just One Second

Google, Microsoft, Meta and Amazon launched a public effort in July to scrap the leap second, an occasional extra tick that keeps clocks in sync with the Earth’s actual rotation. US and French timekeeping authorities concur.

Since 1972, the world’s timekeeping authorities have added a leap second 27 times to the global clock known as the International Atomic Time (TAI). Instead of 23:59:59 changing to 0:0:0 at midnight, an extra 23:59:60 is tucked in.

That causes a lot of indigestion for computers, which rely on a network of precise timekeeping servers to schedule events and to record the exact sequence of activities like adding data to a database. The temporal tweak causes more problems — like internet outages — than benefits, they say. And dealing with leap seconds ultimately is futile, the group argues, since the Earth’s rotational speed hasn’t actually changed much historically.

“We are predicting that if we just stick to the TAI without leap second observation, we should be good for at least 2,000 years,” research scientist Ahmad Byagowi of Facebook parent company Meta said via email. “Perhaps at that point we might need to consider a correction.* The tech giants and two key agencies agree that it’s time to ditch the leap second. Those are the US National Institute of Standards and Technology (NIST) and its French equivalent, the Bureau International de Poids et Mesures (BIPM).

This governmental support is critical, given that ultimately it is governments and scientists — not technology companies — that are in charge of the world’s global clock system.   The leap second change triggered a massive Reddit outage in 2012, as well as related problems at Mozilla, LinkedIn, Yelp and airline booking service Amadeus. In 2017, a leap second glitch at Cloudflare knocked a fraction of the network infrastructure company’s customers’ servers offline.

Cloudflare’s software, comparing two clocks, calculated that time had gone backward but couldn’t properly handle that result. Computers are really good at counting. But humans introduce irregularities like leap seconds that can throw a wrench in the works.

One of the most infamous was the Y2K bug, when human-authored databases recorded only the last two digits of the year and messed up math when 1999 became 2000. A related problem is coming in 2038 when a 32-bit number that some computers use to count the seconds from Jan.

1, 1970, is no longer large enough. And earlier this year, some websites choked when web browsers hit version 100 because they were programmed to deal with only two-digit version numbers.

To ease the problems with computer clocks that don’t like 61-second minutes, Google pioneered the idea of the “leap smear” that makes the leap second’s changes in many tiny steps over the course of a day. Adding a leap second causes problems with computers. And at some point, we’d have to subtract one, too — something that’s never happened — and that would likely uncover new problems.

“It could have a devastating effect on the software relying on timers or schedulers,” Byagowi and Meta engineer Oleg Obleukhov said in a blog post.