Paul van Gerven
30 November 2022

To stay relevant in a highly digitalized world, the official standard time is ditching the leap second.

Governments worldwide have decided it’s too much of a hassle to keep adding leap seconds to official clocks. The practice, which has been in use since 1972, will be suspended for at least a century from 2035 onward in hopes of finding more elegant ways of syncing modern time-keeping methods with Earth’s rotation.

Two time standards are relevant here: Universal Time (UT or UT1) and Coordinated Universal Time (UTC). UT1 reflects historical ways of timekeeping and is based on Earth’s rotation. More precisely, UT1 measures this rotation with respect to distant stars, since precise positional measurements of the sun are difficult. UTC, on the other hand, is based on the steady tick of atomic clocks.

UTC has been defined to match UT1 as best as possible, but since Earth’s rotation isn’t constant, leap seconds have been added whenever UT1 and UTC diverge by more than 0.9 seconds. This has happened 27 times since 1972, when UTC was established (additionally, ten seconds were added to atomic time in that year).

The problem is: those leap seconds are a nightmare in today’s digitalized world. Many systems in communication, finance, transportation and defense rely on precise timekeeping. An added second caused a massive outage of the popular internet forum Reddit in 2012. Social network Linkedin, review website Yelp and internet security company Cloudfare experienced issues too.

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Things were about to get worse. Since Earth’s rotation has been speeding up lately, leap seconds will soon have to be subtracted rather than added, which has never been done before. Some experts fear it will wreak havoc – like the Y2K disaster that was once feared.

Drift apart

Unsurprisingly, tech giants including Amazon, Google and Meta and a number of other companies have called for the leap second to be scrapped. Ironically, however, they’ve also been exacerbating the problem by handling leap seconds differently. Google, for example, lengthens every second a tiny bit in the 24 hours before the leap second. Microsoft, on the other hand, stretches out the second right before the leap second.

Clocks could get even more out of sync if organizations opt for more practical ways of keeping time, which don’t bother with leap seconds. According to an international survey among metrology institutes and other stakeholders, these unofficial clocks have already started to replace UTC. To stay relevant, standard time had to become more tech friendly.

On 18 November in France, the General Conference on Weights and Measures (CGPM) decided to abandon the leap second from 2035, perhaps sooner. The world’s official clock will be atomic, and the difference between atomic and astronomical time will be allowed to drift apart.

While the move is welcomed around the world, Russia, which voted against the proposal, is unhappy. Most global positioning systems effectively sideline the leap second, but Russia’s Glonass incorporates it. As a result, the latter will need to be overhauled. This might even require launching new satellites and constructing new ground stations, an expert told Nature.