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The Future of Leap Seconds

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

Earth in space. Elements of this image furnished by NASA.

Earth's rotation is a part of defining time.

Coordinated Universal Time is a combination of Universal Time - Earth's rotation - and Atomic Time.


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?

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


Leap Seconds

  1. What's a Leap Second?
  2. How Leap Seconds Work
  3. The Future of Leap Seconds
  4. How Long is a Day on Earth?
  5. International Atomic Time (TAI)
  6. How Do Atomic Clocks Work?

Go to Library

Leap Seconds Added

The difference TAI vs. UTC refers to after the leap seconds have been added

UTC DateUTC TimeDifference
1972-06-3023:59:6011 secs
1972-12-3123:59:6012 secs
1973-12-3123:59:6013 secs
1974-12-3123:59:6014 secs
1975-12-3123:59:6015 secs
1976-12-3123:59:6016 secs
1977-12-3123:59:6017 secs
1978-12-3123:59:6018 secs
1979-12-3123:59:6019 secs
1981-06-3023:59:6020 secs
1982-06-3023:59:6021 secs
1983-06-3023:59:6022 secs
1985-06-3023:59:6023 secs
1987-12-3123:59:6024 secs
1989-12-3123:59:6025 secs
1990-12-3123:59:6026 secs
1992-06-3023:59:6027 secs
1993-06-3023:59:6028 secs
1994-06-3023:59:6029 secs
1995-12-3123:59:6030 secs
1997-06-3023:59:6031 secs
1998-12-3123:59:6032 secs
2005-12-3123:59:6033 secs
2008-12-3123:59:6034 secs
2012-06-3023:59:6035 secs
2015-06-3023:59:6036 secs
Further leap seconds not yet announced.

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