Leap seconds are with us until 2023 (at least)

November 20, 2015 // By Graham Prophet
The ITU World Radiocommunication Conference (WRC-15), in session in Geneva, has decided that Coordinated Universal Time (UTC) should retain the “leap second”, and has deferred any future decision on the subject until the 2023 World Radiocommunication Conference, that will again consider a new reference time scale to be considered by in 2023. ITU has the responsibility for distributing UTC.

The issue arises due to the established practice of keeping UTC in step with sidereal (astronomical) time, or in other words, with the time we use day-to-day. As the length of both the day and the year (Earth's rotation and orbit periodicity) varies, adjustments are required to our “timebases”.

This has become an increasingly significant issue as more and more communications (and other) global systems are synchronous on a microsecond (or finer) scale. Providers (e.g. GPS) and users of synchronised time must work in lock-step whenever adjustment (leap) seconds are added or subtracted from UTC. The alternative, widely proposed, is for UTC to maintain a continuous timebase going forward, and not to add/subtract adjustments: which would imply that over longer timescales, it would drift markedly apart from “everyday” time.

The ITU has effectively pushed any final decision on the topic into the future; WRC-15 has decided that further studies are required on the impact and application of a future reference time-scale, including the modification of coordinated universal time (UTC) and suppressing the so-called “leap second”.

Leap seconds are added periodically to adjust to irregularities in the earth’s rotation in relation to Coordinated Universal Time (UTC), the current reference for measuring time, in order to remain close to mean solar time (UT1). A leap second was added most recently on 30 June 2015 at 23:59:60 UTC. The proposal to suppress the leap second would have made continuous reference time-scale available for all modern electronic navigation and computerized systems to operate while eliminating the need for specialized ad hoc time systems.

The decision by WRC-15 calls for further studies regarding current and potential future reference time-scales, including their impact and applications. A report will be considered by the World Radiocommunication Conference in 2023. Until then, UTC shall continue to be applied as described in Recommendation ITU-R TF.460-6 and as maintained by the International Bureau of Weights and Measures (BIPM).

WRC-15 also calls