Expect UTC to keep the leap second for at least another eight years.
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 synchronized 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 earths 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 BIPM (International Bureau of Weights and Measures).
WRC-15 also calls for reinforcing the links between ITU and the BIPM. ITU would continue to be responsible for the dissemination of time signals via radiocommunication and BIPM for establishing and maintaining the second of the International System of Units (SI) and its dissemination through the reference time scale.
The list of interested parties gives an indication of the complexity of the topic; the ITU's statement continues, Studies will be coordinated by ITU along with international organizations such as:
- IMO (International Maritime Organization)
- ICAO (International Civil Aviation Organization)
- CGPM (General Conference on Weights and Measures)
- CIPM (International Committee for Weights and Measures)
- BIPM (International Bureau of Weights and Measures
- IERS (International Earth Rotation and Reference Systems Service)
- IUGG (International Union of Geodesy and Geophysics)
- URSI (International Union of Radio Science)
- ISO (International Organization for Standardization)
- WMO (World Meteorological Organization), and
- IAU (International Astronomical Union).
Modern society is increasingly dependent on accurate timekeeping, said ITU Secretary-General Houlin Zhao. ITU is responsible for disseminating time signals by both wired communications and by different radiocommunication services, both space and terrestrial, which are critical for all areas of human activity.
The worldwide coordination of time signals is critical for the functioning and reliability of systems that depend on time, said Franois Rancy, Director of the ITU Radiocommunication Bureau. ITU will continue to work with international organisations, industry and user groups towards providing coherent advice on current and potential future reference time-scales.