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The Future of Leap Seconds

Leap seconds are added to our clocks to compensate for the Earth's slowing rotation.

Illustration image
©iStockphoto.com/kvkirillov

However, some scientists propose abolishing leap seconds in the future, redefining the way we measure time. This issue will be put to a vote in 2015.

Should Earth's rotation define time?

Triggered by a questionaire about Coordinated Universal Time (UTC) distributed by the IERS in 1999, scientists around the world began discussing the use of leap seconds. The argument revolves around the question:

Should we adjust our clocks to the Earth's slowing rotation, or should
atomic clocks be solely responsible for measuring time?

All leap seconds added so far

YearUTC DateUTC TimeUTC–TAI after insertion
19721972-06-3023:59:60-11 seconds
19721972-12-3123:59:60-12 seconds
19731973-12-3123:59:60-13 seconds
19741974-12-3123:59:60-14 seconds
19751975-12-3123:59:60-15 seconds
19761976-12-3123:59:60-16 seconds
19771977-12-3123:59:60-17 seconds
19781978-12-3123:59:60-18 seconds
19791979-12-3123:59:60-19 seconds
19811981-06-3023:59:60-20 seconds
19821982-06-3023:59:60-21 seconds
19831983-06-3023:59:60-22 seconds
19851985-06-3023:59:60-23 seconds
19871987-12-3123:59:60-24 seconds
19891989-12-3123:59:60-25 seconds
19901990-12-3123:59:60-26 seconds
19921992-06-3023:59:60-27 seconds
19931993-06-3023:59:60-28 seconds
19941994-06-3023:59:60-29 seconds
19951995-12-3123:59:60-30 seconds
19971997-06-3023:59:60-31 seconds
19981998-12-3123:59:60-32 seconds
20052005-12-3123:59:60-33 seconds
20052005-12-3123:59:60-34 seconds
20122012-06-3023:59:60-35 seconds
Further leap seconds not yet announced.

A never-ending argument?

The scientific community has so far failed to reach an agreement on this topic.

  • In 2003, a meeting named “ITU-R SRG 7A Colloquium on the UTC timescale” took place in Torino, Italy, where it was suggested that time be decoupled from the Earth’s rotation and leap seconds be abolished. No decision was reached.
  • In 2005, US scientists proposed to eliminate leap seconds and replace them with leap hours. The proposal was criticized for its lack of consistent public information and adequate justification.
  • In 2012, delegates of the World Radiocommunication Assembly in Geneva, Switzerland, decided once more to postpone the decision to abolish leap seconds and scheduled a new vote for 2015.

Leap seconds: pros and cons

Dr Markus Kuhn (University of Cambridge) lists the following arguments against leap seconds:

  • Leap seconds could cause disruptions where computers are tightly synchronized with UTC.
  • Leap seconds are a rare anomaly, which is a concern for safety-critical real-time systems (e.g. air-traffic control concepts entirely based on satellite navigation).
  • Astronomical time (UT1), which is defined by Earth's rotation, is not significant in most people’s daily lives.

His arguments in favor of leap seconds include:

  • There have been no credible reports about serious problems caused by leap seconds.
  • Some computerized systems that work with leap seconds are costly to modify (eg. antennas that track satellites).
  • Computer errors caused by leap seconds can be avoided simply by using International Atomic Time (TAI) instead of Universal Coordinated Time (UTC).
  • Desktop computers and network servers have no trouble coping with leap seconds.
  • Humankind has defined time by the Earth's rotation for over 5000 years – this tradition should not be given up because of unfounded worries of some air-traffic control engineers.
  • Abandoning leap seconds would make sundials obsolete.

Despite calls by some people to retain leap seconds, atomic time advocates also argued that leap seconds were a burden because they were unpredictable.

Topics: Timekeeping, Earth

In this Article

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Leap Seconds Library

  1. How do leap seconds work?
  2. The Future of Leap Seconds
  3. Intl Atomic time (TAI)

What's a Leap Second?



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