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Statement on the Leap Second and Future of the Universal Coordinated Time (UTC)
January 20, 2012

At the plenary session of Radio Assembly 2012 on January 19, delegates considered the proposed revision to the definition of Universal Coordinated Time.  The United States made a statement, summarized as follows:

“The United States of America supports the proposed revision to the definition of Universal Coordinated Time (UTC), suppressing the use of leap seconds as a part of this time scale.  In formulating this position, the following matters have been taken into account:

  • The use of leap seconds in UTC introduces discontinuities or disruptions into what would be an otherwise uninterrupted, continuous time stream.  Organizations involved with space activities, global navigation satellite systems, telecommunications, network synchronization and electric power distribution have all requested a continuous time scale.
  • The use of leap seconds in UTC adds complexity to systems dependent on precise time keeping.  They require additional software, protocols, and coordination to ensure that no disharmony is introduced to these systems.
  • Leap seconds are not inserted regularly into UTC.  Each leap second requires human intervention at some level.
  • The use of leap seconds introduces the possibility of technical problems each time they are inserted into UTC.  This can impact the safety and reliability of systems dependent on precision time keeping.
  • A variety of continuous “pseudo-time scales” have proliferated to provide a solution to the problems associated with discontinuities in UTC.  The existence of these multiple time scales creates potential problems in operational use and may complicate unnecessarily not only their inter-operability but also their reliability.
  • The United States recognizes that for local time-of-day and for other specialized systems, there is a need for a time scale reckoned with respect to the rotation of the Earth.  This time scale is currently realized as UT1.  It is widely available for these purposes and can fully satisfy the needs of these systems.  The difference between UTC and UT1 can be supplied at a higher level of accuracy than that provided under the present definition of UTC.
  • It is also recognized that for those specialized systems that depend on the coupling of UTC to UT1, it is desired to allow sufficient time for necessary system modifications to be accomplished.  The revised Recommendation gives time for those users to adjust their systems.  If WRC-12 adopts the proposed revisions to Rec. 460-6, the use of leap seconds in the UTC time scale will stop on approximately January 1, 2018.

“In conclusion, the United States supports the proposed revision to Recommendation ITU-R TF.460-6.  The increasing use of, and reliance on, satellite-based navigation and positional reference favors the suppression of leap seconds.  Systems for space activities, global navigation satellite systems, telecommunications, network synchronization, and electric power distribution desire a continuous, uninterrupted time reference.  UTC without leap seconds can provide this.  By suppressing the use of leap seconds in UTC, the repeated effort and cost required of users to successfully accommodate the introduction of each new leap second into UTC would be eliminated.  The safety and reliability of systems dependent on UTC would be improved.”

The general discussion that followed revealed a heightened degree of interest that has not previously existed on this issue.  The plenary chair proposed that work continue in the study group with a view toward consideration of the revision at the World Radiocommunication Conference as early as 2015.  In the time leading up to WRC-15, the study group would undertake additional studies, in consultation with outside organizations with an interest in the issue.  Remaining ITU administrations that have been acquainted with the issue would have the opportunity to become more involved and join a consensus within the Radio Assembly.

The solution formulated by the chair is a significant step forward.  The issue has now risen into prominence, which should allow for a decision that will have the widest possible backing.  The United States considers this development as positive, and will continue to work with other administrations to reach a decision to revise the definition of universal time based on a continuous time stream.