Recommendation 4 of the 98th CIPM (2009)

On the weakness of the present definition of UTC

The International Committee for Weights and Measures (CIPM),

considering that

• the use of Coordinated Universal Time (UTC) as defined in 1972 is negatively affected by steps caused by the unpredictable insertion of an unpredictable number of leap seconds;
• this definition of UTC can not meet the requirements of many existing and future navigation systems needing uniform time;
• alternate time scales, not affected by leap seconds, are being developed and have started to proliferate;
• the need to represent the Earth’s rotation angle in celestial reference systems for use in maritime celestial navigation is either no longer required or can easily be met through values of [UT1 − UTC] as published by the International Earth Rotation and Reference Systems Service (IERS);
• UT1 can fully satisfy needs related to the determination of the Earth rotation angle;
• there must be sufficient lead time allowed for developers of satellite- and land-based navigation system software to accommodate any change in the definition of UTC;
• over the last ten years a number of national and international technical organizations have expressed increasing concerns about the present definition of UTC and the concomitant proliferation of alternate time scales;

recommends that

national and international agencies and relevant scientific unions concerned with the definition of international time scales urgently consider decisions regarding the future definition of UTC so that international agreement can be reached as soon as possible.

DOI : 10.59161/CIPM2009REC4E