Felix W. Landerer and colleagues at the Max Planck Institute for Meteorology in Hamburg say global warming will
slow down speed up Earth’s rotation by changing ocean bottom pressure, in the process shifting mass around:
We find a net transfer of mass from the Southern to the Northern Hemisphere, and a net movement of mass closer towards Earth’s axis of rotation. Thus, ocean warming and the ensuing mass redistribution change the length-of-day by ?0.12 ms within 200 years.
update, with an obvious correction.