WASHINGTON – Global warming caused by increasing manmade
carbon dioxide in the atmosphere will lengthen the day, according
to a study to be published this month by the journal, Geophysical
Research Letters. Researchers at Belgium’s Royal Observatory and
the Catholic University of Louvain, Belgium, lead by Olivier de
Viron, used computer models to analyze the effect of adding one
percent more carbon dioxide to the atmosphere each year, in order
to reach a doubling of the carbon dioxide concentration after 70
years.
Scientists can currently measure the length of the day to an
accuracy of about 10 microseconds (1/100,000 of a second). It
fluctuates slightly, based primarily on changes in atmospheric
winds and ocean currents, which affect Earth’s angular momentum
as it spins on its axis. Angular momentum measures the rotation of
a non-rigid body, such as a planet, including its ability to continue
to spin. As angular momentum is conserved, the solid Earth’s rate
of rotation is affected by the movement of its nonrigid components,
the ocean and atmosphere.
The Belgian scientists estimated the effect of the ocean and
atmosphere, caused by increasing the amount of atmospheric
carbon dioxide by one percent per year and its effect on global
warming, on Earth’s angular momentum. This rate of increase,
they note, is a common scenario, based on current human activity.
They used 14 different computer models, obtained from the
Coupled Model Intercomparison Project, which showed reasonable
agreement, they say.
They find that the length of day would increase as a result of
angular momentum changes associated with global warming,
including variations in surface pressure over land masses, average
surface pressure over the ocean, and zonal winds and currents, that
is, those moving in an east-west or west-east direction. The amount
of lengthening would be small, on the order of microseconds
(millionths of a second) per year, and would be difficult to
distinguish in any given year from naturally occurring variations.
On a scale of decades or longer periods, though, the effect of
global warming on the length of the day would be measurable, the
researchers say. They anticipate an increase of around
11 microseconds (11/1,000,000 of a second) per decade in the
21st century, resulting in a total lengthening of the day by
0.11 (11/100,000 of a second) for the century as a whole.
The study was funded in part by the Belgian Fonds National de la
Recherche Scientifique.
Contact: Harvey Leifert
hleifert@agu.org
202-777-7507
American Geophysical Union
