Since the early 70's, it has become
link standard operating procedure to add a leap second to account for the fact that astronomical time is 2.5ms slower than atomic time. In fact, between
link 1972 and 2016, a total of 27 seconds have been added as the rate of the earth's rotation slowed. Over time, that rate of slowing has, well, slowed, and projections are showing that the change in mass at the earth's poles
link will push the need for a negative leap-second correction as soon as 2026.