Global timekeeping to end leap seconds in 2027, UC San Diego study notes risks

Scientists worldwide have agreed to change how time is kept by moving to "continuous UTC," which will end the practice of adding leap seconds to synchronize clocks with Earth's rotation, according to kpic.com and komonews.com. This change is scheduled to take effect on May 20, 2027.

Leap seconds have been added 27 times since 1972 to adjust for Earth's gradually slowing spin. However, recent observations show Earth's spin is speeding up, which would require removing seconds—something never done before and potentially problematic for software systems, according to a 2024 study published in Nature by Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography at UC San Diego.

The leap second system has worked for about 50 years, but the irregular acceleration of Earth's rotation means negative leap seconds might be needed, posing risks to software that has never handled time moving backward.

An international meeting held on October 15 in Paris finalized the decision to adopt continuous UTC, which will prevent negative leap seconds and maintain a consistent time scale without adjustments based on Earth's rotation.

This change means that clocks will no longer be perfectly synchronized with astronomical time, but it aims to avoid technical issues caused by time adjustments in computing and communication systems.