Earth’s rotational time has slowed by 1 second. Earth is slowing down due to earthquakes, tidal drag, and the weather, and losing approximately two thousandths of a second every day. To allow for syncing up atomic clock time with the Earth’s rotational time the world’s atomic clocks and true Earth time must be reconciled every so often.
The last leap second was added back in 2012, more than a few sites had trouble with the change and were unavailable.
The time of the world is pretty much governed by the International Earth Rotation and Reference Systems Service.
The latest leap second announcement can be found here. When June 30th rolls around, expect to see some outages.
