NASA/Goddard Space Flight Center--EOS Project Science Office
Public release date: 5-Mar-2003

Changes in the Earth's rotation are in the wind

"Because of Earth's dynamic climate, winds and atmospheric pressure
systems experience constant change. These fluctuations may affect how
our planet rotates on its axis, according to NASA-funded research
that used wind and satellite data....
...From year to year, winds and air pressure patterns change, causing
different forces to act on the solid Earth. During El Niño years, for
example, the rotation of the Earth may slow ever so slightly because
of stronger winds, increasing the length of a day by a fraction of a
millisecond (thousandth of a second)."

http://www.eurekalert.org/pub_releases/2003-03/nsfc-cit030503.php