“Ocean tides raised by the Moon put brakes on the Earth’s rotation, slowing the spin at a gradual but unpredictable rate. The deceleration has been ongoing for aeons. At the present pace, compared to the length of a day in atomic time, today stretches 2.5 milliseconds longer than yesterday, and tomorrow will gain 2.5 milliseconds over today. These small daily increments add up to almost one second over the course of a year, but the precise tally rises or falls at the whim of other factors influencing the Earth’s rotation. The more the Earth slows down in future, the more frequently a leap second will intervene in our affairs. They might come as often as quarterly by the year 2250, and then monthly by 2600.”