The International Earth Rotation Service is possibly my favorite name for an international bureaucracy. It give me visions of a Giant Control Lever extending deep into the Earth, with the labels Faster and Slower.
|_ open switch, slower
__ closed switch faster
You can also do it yourself by standing up or laying downThis kind of rate change is referred to as a “decadal variation”, because the changes last ~decade(s). They seem to be due to activity in the earth’s mantle, but it is all very poorly understood.
I wrote about this three years ago: https://dotat.at/@/2020-11-13-leap-second-hiatus.html