The Future of Leap Seconds
Leap seconds are added to our clocks to compensate for the Earth's slowing rotation. However, it has been proposed that leap seconds be abolished in the future, redefining the way we measure time.
UPDATE: The End of Leap Seconds?
In November 2022, the General Conference on Weights and Measures (CGPM)—an international body that decides on global standards for how things are measured—passed a resolution asking the International Telecommunication Union (ITU) to consider changing the way we define civil time. Read the full story.
In Washington DC, the previous leap second occurred on Saturday, December 31, 2016 at 6:59:60 pm.
UTC time was December 31, 2016 at 23:59:60.
Should Earth's Rotation Define Time?
Triggered by a questionnaire 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:
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.
- In 2015, the decision was again deferred to 2023.
- In November 2022, the General Conference on Weights and Measures (CGPM)—an international body that decides on global standards for how things are measured—passed a resolution asking the International Telecommunication Union (ITU) to consider changing the way we define civil time. Read the full story.
Leap Seconds: Pros and Cons
The computer scientist and leap second expert Markus Kuhn from the 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).
- Universal 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 Coordinated Universal 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.