In a historic first, scientists may need to delete a second from global clocks in 2029 due to Earth spinning slightly faster. Since 2020, the planet’s rotation has sped up, shortening the length of a day by about 1.5 milliseconds. If this trend continues, we’ll experience a “negative leap second”—the opposite of the leap seconds occasionally added to keep atomic time aligned with Earth’s rotation.

This shift reflects complex changes in Earth’s inner core and mass redistribution from melting polar ice. While the adjustment isn’t guaranteed, it would mark a significant milestone in how we measure time.