Nº 7 2013 > The future of time –
To abolish or not to abolish the leap second?

Keeping the world’'s time –
ITU leading international cooperation

Dr Hamadoun I. Touré, ITU Secretary‑General

Dr Hamadoun I. Touré, ITU SecretaryGeneral Six views of the Earth as it rotates over a two-hour period. Each photo was taken after 30 degrees of rotation
Dr Hamadoun I. Touré, ITU Secretary‑General
Six views of the Earth as it rotates over a two-hour period. Each photo was taken after 30 degrees of rotation

Timekeeping is critical to the functioning of modern society, and international coordination is crucial. Coordinated Universal Time, better known by its acronym UTC, is the legal basis for timekeeping for most countries in the world, and is the de facto time-scale in most others. UTC is defined by ITU’s Radiocommunication Sector (ITU-R).

The current standard, Recommendation ITU-R TF.460-6, entitled “Standard-frequency and time-signal emissions”, recommends the application of leap seconds to maintain UTC close to Universal Time 1 (UT1) — a time proportional to the rotation angle of the Earth on its axis. The leap second came into use in 1972.

A number of years later, some administrations expressed concerns about the implementation of the leap second, and a study question on the future of the UTC time-scale was adopted in 2000. Proposals have been made since 2003 to revise Recommendation ITU-R TF.460-6 in order to achieve a continuous time-scale. Noting that the broader implications of changes to the definition of UTC require additional study with wider participation from ITU Member States and external organizations, the World Radiocommunication Conference in 2012 (WRC-12) called for further studies, postponing the decision to WRC-15. As a result, leap seconds will again be reviewed in 2015.

WRC-12 also asked that its Resolution 653, on the future of the UTC time-scale, be brought to the attention of relevant organizations. In line with this instruction, I have consulted with the International Maritime Organization, the International Civil Aviation Organization, the General Conference of Weights and Measures, the Consultative Committee for Time and Frequency, the International Bureau of Weights and Measures (BIPM), the International Earth Rotation and Reference Systems Service, the International Union of Geodesy and Geophysics, the International Union of Radio Science, the International Organization for Standardization, the World Meteorological Organization and the International Astronomical Union.

I am pleased to report that this consultation resulted in a workshop on the future of the international time-scale, jointly organized by ITU and BIPM, which was held from 19-20 September 2013 in Geneva.

WRC-12 noted that the sporadic insertion of leap seconds may upset systems and applications that depend on accurate timing. Some organizations involved with space activities, global navigation satellite systems, metrology, telecommunications, network synchronization and electric power distribution have requested a continuous time-scale.

For other specialized systems and for local time-of-day, however, a time-scale reckoned with respect to the rotation of the Earth is needed. Also, a change in the reference time-scale may have operational and hence economic consequences. ITU-R studies take these considerations into account.

WRC-15 will “consider the feasibility of achieving a continuous reference time-scale, whether by the modification of UTC or some other method, and take appropriate action, taking into account ITU-R studies”.

Meanwhile, let me encourage Member States to continue participating in our studies by submitting contributions to ITU-R.


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