Earth May Spin Faster as Glaciers Melt

Melting ice triggered by global warming may make Earth whirl faster than before.

Melting ice triggered by global warming may make Earth whirl faster than before and could shift the axis on which the planet spins, researchers say.

This could also affect sunset times, as the length of Earth's day depends on the speed at which the planet rotates on its axis. Prior research found the rate at which Earth spins has changed over time.

For instance, ancient Babylonian, Chinese, Arab and Greek astronomers often recorded when eclipses occurred and where these phenomena were seen. This knowledge, in combination with astronomical models that calculate what the positions of the Earth, sun and moon were on any given date and time, can help reveal how fast Earth must have been spinning. To do so, researchers calculate the speed necessary for the planet to face the sun and moon in ways that allowed those astronomers to observe the eclipses. [50 Amazing Facts About Earth]

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In general, the gravitational pull of the moon and sun on Earth is relentlessly slowing the planet's rate of spin. However, in the short term, a variety of different factors can also speed up and slow down how fast Earth whirls.

Previous research has found that melting glaciers triggered by global warming helped cause a significant amount of global sea-level rise in the 20th century. In theory, rising sea levels - once estimated to be climbing at a rate of about 0.06 to 0.08 inches (1.5 to 2 millimeters) per year - should also have slightly shifted Earth's axis and increased the rate at which the planet spins.

When polar ice caps melt, they remove weight off underlying rock, which then rebounds upward. This makes the poles less flat and the planet more round overall. This should in turn cause Earth to tilt a bit and spin more quickly.

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However, previous research mysteriously could not find evidence that melting glaciers were triggering a shift in either Earth's rotation or axis that was as great as predicted. This problem is known as "Munk's enigma," after oceanographer Walter Munk at the Scripps Institution of Oceanography in La Jolla, California, who first noted the mystery, in 2002.

Now, in a new study, researchers may have solved this enigma and shown that rising sea levels are indeed affecting Earth's spin and axis.

"The rise of sea level and the melting of glaciers during the 20th century is confirmed not only by some of the most dramatic changes in the Earth system - for example, catastrophic flooding events, droughts heat waves - but also in some of the most subtle - incredibly small changes in Earth's rotation rate," said study lead author Jerry X. Mitrovica, a geophysicist at Harvard University in Cambridge, Massachusetts.

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First, the scientists noted that recent studies suggested 20th-century glacial melting was about 30 percent less severe than Munk assumed. This should significantly reduce the predicted amount of shift in Earth's spin and axis.

Moreover, the research team's mathematical calculations and computer simulations found that prior research relied on erroneous models of Earth's internal structure. This meant previous studies did not correctly account for how much glaciers would deform underlying rock and influence Earth's spin.

Furthermore, interactions between Earth's rocky mantle and the planet's molten metal outer core should have helped slow the planet's spin more than was previously thought.

Melting Glaciers: Photos

Altogether, these adjustments helped the scientists find that ongoing glacial melting and the resulting sea-level rise are affecting the Earth in ways that match theoretical predictions, astronomical observations, and geodetic or land-survey data.

"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," Mitrovica 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 said. "By resolving Munk's enigma, we further strengthen the already-strong argument that we are impacting climate."

The scientists detailed their findings online today (Dec. 11) in the journal Science Advances.

Original article on Live Science.

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Sea ice off northern Baffin Island in the Arctic.

The Aletsch Glacier in Switzerland

This typical valley glacier is the largest one in the Alps. The glacier's volume loss since the middle of the 19th century is well visible from the trimlines to the right of the image.

Greenland ice caps

This image shows some local (or peripheral) glaciers and ice caps in eastern Greenland in the foreground and the ice sheet with its outlet glaciers (upper right) in the background. Thanks to a new glacier inventory for all of Greenland, it was for the first time possible to determine the sea-level rise contribution from the local glaciers and ice caps on Greenland separately from those of the ice sheet.

The Belcher Glacier on Devon Island in Nunavut, Canada

A Canadian researcher maintains a time-lapse camera overlooking the Belcher Glacier. Monitoring the ice that breaks off from the glacier helps the researchers constrain how much ice is calving into the ocean.

Snow Pit

Glacier Researchers digging a four-meter (13 ft) snow pit to examine annual snow layers on the Devon Island Ice Cap in Nunavut, Canada.

Aerial view of Sverdrup Glacier

The Sverdrup Glacier -- a river of ice in Nunavut, Canada -- flows from the interior of the Devon Island Ice Cap into the ocean.

Glacial Motion

A small valley glacier exits the Devon Island Ice Cap in Nunavut, Canada.

Arctic ice melt

This Landsat satellite image shows the small ice caps located on the southern coast of Ellesmere Island in Nunavut, Canada.

Argentina ice

The Upsala Glacier in Argentina's Los Glaciares National Park flows out from the Southern Patagonian Ice Field.

Argentina ice

The terminus of the Upsala Glacier is at Lago Argentino.

Argentina ice

The Perito Moreno Glacier in Argentina also flows from the Southern Patagonian Ice Field located in the Andes.

Argentina ice

The Perito Moreno Glacier is one of the major tourist attractions in southern Patagonia.

Alaska's Columbia Glacier

Meltwater pools in the accumulation zone of the glacier in July 2008.

Alaska's Columbia Glacier

Crevasses are also seen in the accumulation zone of the glacier in July 2008.

Alaska's Columbia Glacier

The glacier retreated 14 kilometers between 1984 and 2004. Here the terminus of the glacier is seen in June 2004.

Alaska's Columbia Glacier

A stranded iceberg at the Columbia Glacier moraine shoal in Prince William Sound, Alaska, in July 2010.