These very small changes in the Earth s rotation speed mean changes in the length of the day, amounting to a few thousandths of a second over a time span of a decade.
(s rotation speed; mean; ) (changes in the length of the day; amounting; to a few thousandths of a second; T:over a time span of a decade)
s rotation speed changes in the length of the day
mean amounting
to a few thousandths of a second T:over a time span of a decade