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CAMBRIDGE, Mass., Dec. 15 (UPI) -- Previous research proves the rotational speed of the Earth is not fixed. Now, new evidence suggests rising sea levels are slowing our movement around the axis ever so slightly. In the long term, the gravitational interplay between the Earth, sun and moon is slowing the planet's spin, but research shows the Earth's rotation can be sped up or slowed down in the short term by a variety of factors.
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One of those factors was believed to be glacial melting and sea level rise. As melting glaciers shift Earth's mass from the poles to the equator, the Earth's rotation slows. Because glacial melting occurs unevenly -- and water moves -- the uneven shifting of Earth's mass is believed to cause a slight wobble in Earth's axis.
But in 2002, oceanographer Walter Munk showed significant glacial melting and sea level rise hadn't affected Earth's rotation or axis position as previous models predicted they would. The quandary became known as "Munk's enigmna."
That enigma may now be solved thanks to new calculations from researchers at Harvard University and the University of Alberta, in Canada. The findings were published this week in the journal Science Advances.
Recent studies show Munk relied on data that overestimated sea level rise during the 20th century. Newer calculations suggest sea level rise was about 30 percent less dramatic.
Scientists at Harvard and Alberta also looked at models used by Munk to predict the effects of glaciers on Earth's bedrock and the molten core beneath over time. They found that earlier models misunderstood Earth's internal structure.
The deformation of the mantle caused by glaciation during the Ice Age had been overestimated, researchers determined.
"Over the past 3,000 years, the core of the Earth has been speeding up a little, and the mantle-crust on which we stand is slowing down," study co-author Mathieu Dumberry, a physics professor at Alberta, explained in a press release.
Furthermore, more recent and accurate calculations of the Earth's spin -- derived from satellite, astronomical and land-based data -- show very slight decreases in the rate of Earth's rotation, decreases that agree with predictions based on updated glacial melting and seal level rise models.
"What we believe in regard to melting of glaciers in the 20th century is completely consistent with changes in Earth's rotation measured by satellites and astronomical methods," lead study author Jerry Mitrovica, a geophysicist at Harvard University, told Live Science. "This consistency was elusive for a few years, but now the enigma is resolved."
"Human-induced climate change is of such pressing importance to society that the responsibility on scientists to get things right is enormous," Mitrovica added. "By resolving Munk's enigma, we further strengthen the already-strong argument that we are impacting climate."
But not everyone is buying Mitrovica's solution to the enigma.
While William Richard Peltier, a professor of physics at the University of Toronto, thinks the new paper makes some interesting and important points about the rotational relationships between mantle and core, he thinks the scientists' recalibration of Ice Age models is misguided.
It's a misstep he says undermined the overall conclusions.
"Nice try, but no cigar," he told the Washington Post.
But Mitrovica and Dumberry are adamant about the solution -- one they say lends confidence to the ongoing work of predicting sea level rise through the end of the century.
"This can help to better prepare coastal towns, for example, to cope with climate change," said Dumberry. "We're talking billions of dollars of infrastructure here."
