German geophysicist Felix W. Landerer of the Max Planck Institute for Meteorology (Hamburg, Germany) led a team of researchers in the modeling of the Earth based on estimates from the Intergovernmental Panel on Climate Change. If carbon dioxide levels double between 2000 and 2100, then the length of a day, by the year 2200, will be reduced by about 0.12 milliseconds. Every 100 years, a day will be shortened by about 0.23 milliseconds due directly to global warming.
According to New Scientist, Landerer compares this effect with an ice skater: "Think of an ice skater who is spinning. When you stretch your arms out you slow down, and when you bring your arms closer to your body you spin faster."
This supposed increase in the spin rate of the Earth is caused by the increasing temperatures of the Earth’s oceans, which causes changes in global density and circulation, which causes a transfer of more mass to the higher latitudes (closer to the North and South Poles, and nearer to the Earth’s axis of rotation; and away from the equator, which is further from the rotational axis of the Earth), which, in the end, causes the Earth to rotate faster and each day to be just a little bit shorter.
The result of Landerer’s study appears in the journal Geophysical Research Letters (volume 34, page L06307).