[gshubert17]

What happened to the rotation rate around the beginning of 2019, to cause the big change in the slope of the UT1-UTC line (https://crf.usno.navy.mil/ut1-utc)? After adding 5 leap seconds in 11 years, no leap seconds have been added or subtracted since the end of 2016.

[techdragon]

Its probably not the only component... but a fun fact is that the Earth's rotation is affected by the average equatorial ocean temperatures, (anyone seen the ocean temperature charts this year... something something ships and sulfur dioxide accidental geoengineering that we stopped doing) warm ocean water displaces slightly more volumetrically and thus by way of its lower density, affects the spinning mass balance of the Earth like a ice skater curling in their fingers rather than their whole arms while spinning like a top, the effect is there... just so very subtle.

[fanf2]

As far as I know it is still an open question.

This 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