The negative leap second could end up shortening the year, but the IERS shows no new leap seconds scheduled to be added or subtracted.
According to the National Institute of Standards and Technology (NIST), "a leap second is a second added to Coordinated Universal Time (UTC) to keep it synchronized with astronomical time/universal time (UT1). UTC is an atomic time scale based on the performance of atomic clocks that are more stable than the Earth's rotational rate. Astronomical time (UT1), or universal time, is based on the rotation of Earth, which is irregular". The last addition came in 2016, when on New Year's Eve at 23 hours, 59 minutes and 59 seconds, an extra "leap second" was added.
However, in 2021, scientists might have to subtract a second, calling it a "negative leap second." This will happen for the first time ever. The International Earth Rotation and Reference Systems Service (IERS) measures Earth's rotation and confirms the difference between UT1 and UTC. It determines the next positive or negative leap second depending on the evolution of the difference between Universal time(UT1) and Atomic time(TAI). On Jan. 7, 2021, it released a bulletin on the UCT and International Atomic Time(TAI). The current difference between UTC and TAI is minus 37 seconds, which means that there will be a 19 millisecond lag in atomic time at the end of this year. This also means that 2021 could be shorter than the other years in 50 years or half a century.
Physicist Peter Whibberley of the National Physics Laboratory told the Telegraph, "It's quite possible that a negative leap second will be needed if the Earth's rotation rate increases further, but it's too early to say if this is likely to happen. There are also international discussions taking place about the future of leap seconds, and it's also possible that the need for a negative leap second might push the decision towards ending leap seconds for good," LiveScience reported.
According to the service's Earth Orientation Center, the IERS shows no new leap seconds scheduled to be added, which officially measures the length of a day.