year getting shorter

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Ocean bottom pressure changes lead to a decreasing length-of-day in a warming climate. We use a coupled climate model to evaluate ocean bottom pressure changes in the IPCC-A1B climate scenario.

Most prominently, the Arctic Ocean shelves experience an above-average bottom pressure increase. 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, demonstrating that the oceans are capable of exciting nontidal length-of-day changes on decadal and longer timescales.
Felix W. Landerer and others, Geophysical Research Letters, Vol 34, Issue 6, March 2007.