The International Conference on Weights and Measures decides to cancel leap seconds

China News Service, Beijing, October 19 (Reporter Liu Liang) China's State Administration for Market Regulation announced on the 19th that the 28th International Conference on Weights and Measures (CGPM) recently held in Versailles, France, decided to stop inserting leap seconds globally from May 20, 2027, and to relax the maximum allowable deviation between Coordinated Universal Time (UTC) based on atomic clocks and Universal Time (UT1) based on the Earth's rotation to 3600 seconds (1 hour).

Since 1972, the world has used UTC as the basis for civil standard time, and the time difference with UT1 has been controlled within 0.9 seconds by inserting leap seconds from time to time. Since the earth's rotation time is difficult to accurately predict, there is no fixed period for inserting leap seconds. A positive leap second is 61 seconds long, and a negative leap second is 59 seconds, resulting in discontinuous time. So far, 27 positive leap seconds have been inserted, and no negative leap seconds have yet been inserted.

It is reported that the leap second mechanism has caused real risks to the economic and social operation. When a positive leap second is inserted, a special moment of "23:59:60" will occur. Many systems are insufficiently adapted and can easily cause failures. In 2025, the International Time and Frequency Advisory Committee (CCTF) pointed out that given that the earth's rotation is accelerating, the probability of inserting a negative leap second for the first time in the next few years is very high, and the global system has generally not tested adaptation, and the insertion of a negative leap second may have a greater impact on the economy and society.

The State Administration for Market Regulation said that it will strengthen situation analysis and analysis with relevant departments to ensure that China’s standard time is independent, safe, controllable, and operates smoothly, and to promote the harmonization of global standard time. (over)