Leap seconds are with us until 2023 (at least)
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 for reinforcing the links between ITU and the International Bureau of Weights and Measures (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 organisations such as the International Maritime Organisation (IMO), the International Civil Aviation Organisation (ICAO), the General Conference on Weights and Measures (CGPM), the International Committee for Weights and Measures (CIPM), the International Bureau of Weights and Measures (BIPM), the International Earth Rotation and Reference Systems Service (IERS), the International Union of Geodesy and Geophysics (IUGG), the International Union of Radio Science (URSI), the International Organisation for Standardisation (ISO), the World Meteorological Organisation (WMO), and the International Astronomical Union (IAU).
“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 François 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.”
ITU; www.itu.int
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