Since 1972, Earth has synchronized its time with its rotation by adding leap seconds 27 times, the last time being in 2016. As Earth’s rotation accelerates, the probability of negative leap seconds is expected to reach 30% by 2035, which may cause system disruptions. The International Bureau of Weights and Measures proposes using leap hours instead of leap seconds, with adjustments made when the time difference reaches 3600 seconds. This proposal will be voted on at the 28th Conference on Weights and Measures held outside Paris in October 2026.
Leap seconds may be abolished, replaced by leap hours. Since 1972, Universal Time Coordinated (UTC) has been adjusted 27 times by adding leap seconds to stay synchronized with Earth's rotation, with the last adjustment in 2016. However, leap seconds could become negative—meaning a second is skipped—something that has never happened before and could cause disruptions in computer systems, affecting critical infrastructure such as power grids, communications, finance, and the internet. Since 2015, Earth's rotation has accelerated, and scientists estimate that the probability of a negative leap second occurring by 2035 reaches 30%. To mitigate these risks, the International Bureau of Weights and Measures (BIPM) has proposed replacing leap seconds with leap hours, adjusting only when the time difference reaches 3600 seconds. This proposal will be voted on during the 28th General Conference on Weights and Measures, scheduled from October 13 to 15, 2026, held outside Paris.