With Leap Second, You’re Done With 2016, But 2016 Isn’t Done With You

New Year's Eve will last one second longer to keep world's clocks in sync with Earth's rotation

Illustration: R. A. Di Ieso
Dec 30, 2016 at 12:52 PM ET

As the global annus horribilis that is 2016 comes to a merciful end, only one question really remains: What finishing move could this absurd year possibly have in store? Well, how about an extra second added to the last day in 2016, which, if it’s anything like the last leap second, could create chaos and outages for computer systems? Yes. That will do nicely.

Since 1972, the world has had to add 26 extra seconds to keep the world’s clocks in sync with the Earth’s gradually slowing rotation. The length of a day doesn’t change that much — only about a microsecond or two per century — but that adds up when every year has more than 30 million seconds. So to keep time on track, the International Earth Rotation and Reference Systems Service, or IERS, announces the addition of an extra second, either at the precise mid-year point of midnight on June 30 or, in this case, midnight on New Year’s Eve.

The IERS adds the leap second whenever it’s necessary to keep the clocks within 0.9 seconds of solar time. From 1972 to 1998, this meant adding a leap second close to every year, but things have slowed down a lot since then, with only five extra seconds added in the last 18 years. Perhaps the relative rarity of leap seconds during the rise of the modern internet helps explain why so many sites have been downright flummoxed when asked to cope with the notion of a repeated second. The two most recent leap seconds, in June of 2012 and 2015, brought down or caused wonkiness for Mozilla, Reddit, Foursquare, Yelp, LinkedIn, StumbleUpon, Netflix, Pinterest, Amazon, Twitter, and the Android operating system, not to mention grounding 400 Qantas flights in 2015 when the Australian airline’s online check-in system crashed.

But those last two leap seconds were mid-year additions, meaning they don’t carry the same numerological potency of one happening on New Year’s Eve, a time long associated with potential computer chaos. When the most recent year-end leap second in 2008 caused all the world’s Zune MP3 players — yes, all 27 of them — to freeze up, worried Zune owners dubbed the crisis Y2K9, which was maybe slightly overstating the danger of a world without the Zune.

More Why A Top US Naval Scientist Is Terrified Of The Leap Second

Several of the internet’s biggest groups have plans in place to keep disruptions this time around to a minimum. Google, for instance, uses what’s known as a “leap smear,” where it skips the extra second but makes all its seconds a tiny bit longer for 20 hours on New Year’s Eve. By making each second only 14 microseconds longer than normal, the discrepancy between Google’s clocks and those of the rest of the world are minimal, within the margin of noticeable error for most computer systems. Amazon and Microsoft have planned similar 24-hour smears.

Google will switch to a daylong smear for the next leap second, likely sometime in 2018, and has called for the internet as a whole to adopt this as standard practice. Otherwise, as they point out, the leap seconds and smears kind of defeat the purpose of clocks, which is to have everyone the same time, even if the difference is a matter of microseconds.

Some disruptions are certainly possible this New Year’s Eve, especially since the Linux operating system in particular dislikes the leap second, though workarounds are out there. And not all the potential problems are as benign as Netflix or Reddit crashing for a little bit. For instance, the leap second will create a discrepancy between the world’s clocks and the global positioning system, which doesn’t use the leap second. Australian farmers could find their GPS not working properly on New Year’s morning, which is a small but real issue during harvest time.

The leap second occurs on midnight on Greenwich mean time, so only those in the United Kingdom, Ireland, Portugal, and much of western Africa can rightfully add an extra “one” to their New Year’s countdown. For those in the Americas, the extra second will slip quietly by in the evening of December 31, while in the eastern hemisphere the leap second will occur on January 1, so half the world gets a regular-length 2016 and a slightly extended 2017. Before calling them the lucky ones, consider this: Maybe the leap second isn’t 2016’s way of prolonging our misery, but rather one last, futile effort to hold off whatever is coming next.