By Michael Pearson
Classify this under the "things you may not have known": Climate change, scientists say, is slowing the Earth's rotation very slightly.
It is not a new idea. In fact, for years scientists have been searching for the relationship between melting glaciers, rising sea levels, and a slowdown of the Earth.
However, it is taking a new turn since the publication of a document that relates the average rise in sea level during the 20th century with the slowing down of the Earth's rotation.
It turns out that the water that is derived from melting glaciers and moving away from the poles acts like the outstretched arms of an ice skater, making each rotation much slower, said Jerry Mitrovica, a professor of geophysics at the University of Harvard and lead author of the article.
In the case of Earth, it is one millisecond a day. That's one thousandth of a second.
It might not sound like much, but that decline coincides very well with the effect of global average sea-level increases of 1 to 1.5 millimeters during the 20th century, Mitrovica said. That's the total amount that glaciologists have estimated after looking at what has happened to all the world's glaciers, he said.
So it's really more about confirming the effects of climate change than anything else, he said.
His research is a response to a 2002 paper by oceanographer Walter Munk, who found discrepancies between the rate of deceleration of the Earth's rotation and theories about the average rise in sea level over the century.
Munk used an incorrect model for how the last ice age 5,000 years ago continues to affect the Earth's rotation, Mitrovica said.
By using a more recent model and rotation information cross-referenced to older astronomical observations, Mitrovica was able to show that the estimated changes in rotation and sea level changes fit precisely.
Rotation from melting glaciers is above a slowdown caused by the forces of tides, winds and other impacts, adding about 1.4 milliseconds to a day over the course of a century, according to the Naval Observatory of U.S.
Other things can affect the rotation of the Earth as well. A 2011 earthquake in Japan reportedly shortened the day by 1.8 millionth of a second, according to NASA.
Although the research seems esoteric and the implications of a slower spinning planet are not very significant, in practical terms, Mitrovica says, it provides another tool to help assess the level of melting.
"It gives you a simple, uncontaminated measurement of what is happening to the Earth's ice sheets and glaciers," he said.