File this under Things You May Not Have Known: Climate change, scientists say, is slowing Earth’s rotation ever so slightly.
It’s not a new idea. In fact, scientists have been looking at the relationship among melting glaciers, rising sea levels and a slowing Earth for years.
But it’s getting a new airing after publication of a paper matching the mean rise in sea levels during the 20th century to the slowdown in Earth’s spin.
It turns out that water melting off glaciers and moving away from the poles acts much like an ice skater’s outstretched arms, making every rotation that much slower, said Jerry Mitrovica, a Harvard University professor of geophysics and lead author of the paper.
How much slower?
In Earth’s case, one millisecond a day. That’s a thousandth of a second.
It may not seem like much, but that slowing matches up nicely with the effect of average global sea level increases of 1 millimeter to 1.5 millimeters during the 20th century, Mitrovica said. That’s the total amount glaciologists have estimated after looking at what’s happened to all the world’s glaciers, he said.
So it’s really more about confirmation of 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 slowing in Earth’s rotation and prevailing theories about average sea level increases over the century.
Mitrovica said Munk used an inaccurate model for how the last ice age 5,000 years ago continues to affect Earth’s rotation.
By using a newer model, and cross-referencing rotation information with ancient astronomical observations, Mitrovica was able to show that rotation changes and estimated sea level changes fit precisely.
The rotation from melting glaciers is on top of slowing caused by tidal forces, winds and other impacts, which adds about 1.4 milliseconds to a day over the course of a century, according to the U.S. Naval Observatory.
Other things can also effect Earth’s rotation. A 2011 earthquake in Japan is said to have shortened the day by 1.8 millionth of a second, according to NASA.
While the research seems esoteric and the implications of a more slowly spinning planet won’t amount to much, practically speaking, Mitrovica says, it does provide another tool to help assess how much melting is going on.
“It gives you one, simple, unpolluted measurement of what the Earth’s ice sheets and glaciers are doing,” he said.