April 21, 2009 -- Climate change will make the day longer by the end of the century, according to a new study.
Earth's atmosphere plays a large role in controlling how fast the planet rotates. As the seasons change, variations in high-level jets of wind shift, adding and subtracting about a millisecond to our day each year.
Elfrun Lehmann of the Free University of Berlin in Germany and a group of researchers compared wind patterns measured between 1982 and 2000 to a computer model that projected conditions from 2071 to 2100.
They found that Earth's days will lengthen by an average of half a millisecond in the future if carbon dioxide doubles compared to preindustrial levels, thanks mostly to increasingly warm "El Nino" conditions in the tropical Pacific Ocean.
"After 2050 you get more strong El Ninos," Lehmann said. "El Ninos lead to extensive increase in jets in the upper troposphere."
Lehmann presented his research in a meeting this week of the European Geosciences Union.
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Between 1982 and 2000, there were three strong El Nino events. By comparison, as many as 50 such events have been forecast for the 21st century. Each El Nino can slow Earth's rotation enough to increase day length by about a millisecond, but it is usually not a cumulative effect -- it subsides as the Pacific's waters cool near the equator.
But global warming figures to pump ocean surface temperatures up consistently, forcing ever more frequent El Ninos. As warm, humid air rises from the sea, it imparts energy on jets of wind that course around the planet at an altitude of between 22 and 50 kilometers (16.7 and 30.1 miles), and can reach speeds in excess of 450 miles per hour.
As the winds increase in speed, the solid Earth will respond by slowing down slightly.
"Earth is a closed system, so as something changes in one part, another has to compensate," Jean Dickey of Jet Propulsion Laboratory in Pasadena, California said. "They're small changes -- you don't have to reset your watch."
There's no telling how much the planet would slow if global warming were to increase indefinitely. To a large degree, atmospheric circulation controls how long the day is, but ocean currents and tides play a role, too.
Dickey suspects that if winds increased or decreased dramatically, these other mechanisms would begin to change, preventing the day from becoming much longer.
Related Links:
European Geosciences Union 2009 Meeting Overview
Discovery Earth for interviews, images and more.
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