As Earthâs rotation speed slowed ever-so-slightly in recent decades, leap seconds were added intermittently to keep clocks up to date. But if a new trend holds, time might need to be turned in the other direction some day soon. Earlier this month, The Daily Telegraph reported that Earth has reached its quickest spin speeds in the past half-century. âItâs quite possible that a negative leap second will be needed if Earthâs rotation rate increases further,â said Peter Whibberley, a senior research scientist with Britainâs National Physical Laboratory, according to The Daily Telegraph. The speed of Earthâs spin fluctuates constantly due to a range of factors, including the motion of the planetâs core and oceans, according to the British newspaper.